Know how to prepare surfaces for decoration 2

UNIT 2019 Know how to prepare surfaces for decoration 2 Surface preparation is very important for producing a high-quality finish. In this unit we wi...
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UNIT 2019

Know how to prepare surfaces for decoration 2 Surface preparation is very important for producing a high-quality finish. In this unit we will look at some typical surfaces you may find yourself working on during your career, along with appropriate preparation tasks for each surface. It is important that all surface contaminants such as dirt, oil, rust and loose or flaking existing coatings are removed. If these contaminants are not removed, it could affect whether the paint or paper will adhere (stick) to the surface. This unit also contains material that supports NVQ unit QCF 332 Prepare surfaces for Painting/Decorating. This unit also contains material that supports TAP Unit Prepare surfaces for Painting/Decorating.

This unit covers the following learning outcomes: Preparing timbers and timber sheet products ready to receive finishing systems Preparing metal surfaces ready to receive finishing systems Preparing trowelled finishes and plasterboard ready to receive finishing systems Removing previously applied paint and paper ready to receive finishing systems Rectifying surface conditions Repairing and making good surfaces


Level 2 NVQ/SVQ Diploma Painting and Decorating 3rd edition

K1. Preparing timbers and timber sheet products ready to receive finishing systems Timber is one of the most commonly used materials in construction. You will encounter timber in a wide range of situations, both internal and external.

Key terms Botanical – the classification of trees based on scientific study

Unit 2019 Know how to prepare surfaces for decoration 2

Deciduous – the name given to a type of tree that sheds it leaves every year Evergreen – the name given to a type of tree that keeps its leaves all year around


Applications of timber and timber sheet products Types of timber Timber is classified as either softwood or hardwood. This can sometimes be confusing as not all hardwoods are physically hard or softwoods soft. Hardwood and softwood refers to the botanical differences and not the strength of the timber. Hardwood trees are deciduous, broad leaved, with an encased seed. Softwood trees are usually evergreen with needles and seeds held in cones.




Redwood (commonly known as pine)

Moderately strong for its weight with average durability. Quality of finish depends on knots and amount of resin. Capable of smooth, clean finish and can be glued, stained, varnished and painted.

Used for interior or exterior work and for carcassing and finish joinery

Whitewood (also known as European Spruce)

Similar to redwood in strength and durability. Takes glue, nails and screws well and can produce a good finish.

Similar uses to redwood

Western red cedar

Not as strong as redwood but has naturally occurring oils which prevent insect attack. Doesn’t need treating as will stand up to severe weather and turns a silvery colour when exposed.

Externally for good-quality timber buildings, saunas, etc.

Table 19.1 Commonly used softwoods






Very strong with English oak the strongest. Good resistance to bending and shearing. Susceptible to fungi attack and ironwork should not be used as it will stain and disfigure.

High-class joinery, panelling, doors, exposed roofing, etc.


Hard, close grained and durable with a fine texture. Capable of a good smooth surface. Takes glue, stains and polish well and can produce an excellent veneer.

Furniture, kitchen utensils, wood block floors, etc.


Strong for its weight and moderately resistant to decay. Takes glues, finishes, nails and screws well.

High-class joinery, furniture, boat building and plywood veneers




Made from thin layers of timber glued together to form boards. Alternating grain across and along the sheet gives strength and stability.

Used in floors, walls and roofs


Made from pulped wood mixed with adhesives and pressed into sheets. Moisture resistant MDF is available.

Skirting boards and mouldings


Manufactured from sugar cane pulp mixed with adhesives and pressed into sheets 3–6 mm thick. Has a reasonable resistance to moisture.

Flooring, furniture and units

Table 19.2 Commonly used hardwoods Name


Know how to prepare surfaces for decoration 2


Unit 2019

Unit 2019 Know how to prepare surfaces for decoration 2

Table 19.3 Commonly used timber sheet products


Level 2 NVQ/SVQ Diploma Painting and Decorating 3rd edition

Uses of timber Timber has several different uses in the construction industry. You will be familiar with some of these uses, particularly structural uses, from Unit 2003, pages 81–85 and page 88. Structural – floors, walls and roofs providing stability to the building. Timber is a core part of the construction or as decking over a framework. l First fixing – any work inside a structure before plastering takes place. Includes studwork, ground lats, stairs, windows and doors. l Second fixing – any work inside a structure after plastering has taken place. Includes all joinery work, such as doors, architrave, units and ironmongery. l Decorative – any structure made entirely from timber such as fire surrounds, mouldings, balustrades, banisters, dado rails, flooring and decking/fencing. l

Unit 2019 Know how to prepare surfaces for decoration 2

Safety tip Knotting solution is highly flammable and so should not be exposed to naked flames. You must also make sure you wear the appropriate PPE when handling this material.

Timber can be affected by a wide range of defects. If you are not sure what preparation or decoration is required for a particular type of timber, you should always seek advice before starting the task.

Knotting and resin exudation A knot is a place in the timber where a branch was joined to the tree. Resin may bleed from knots, staining the paint finish. Knotting solution seals knots and can be applied to areas stained with resin, tar and ink. Its main ingredient is shellac, produced by an insect and melted into thin flakes. Clean and dry the surface before applying with a brush. It should dry quite quickly, after which time the surface coating can be applied. Figure 19.1 Knotting bottle Key term Resin – a natural liquid formed in wood when it is converted into useable timber. Very sticky and usually yellowish gold, under heat it emerges from knots (this is called resin exudation)


Defects in timbers and timber sheet products, and treatments

Stain sealing Shellac is also available coloured (known as pigmented shellac). Aluminium provides a silver pigment while titanium provides a white pigment, and these are very effective stain sealers especially on: stains made by fire, smoke and water l previously creosoted timber l animal, smoke and fire odours (smells). l

Unit 2019 Know how to prepare surfaces for decoration 2

End grain, open grain and cracks

Did you know?

Wood grain is the growth rings found inside all tree trunks. When timber is cut in the opposite direction of these rings this is called cutting ‘against the grain’ and it can cause timber to chip or tear. Other grain cuts include:

Shellac is not only used in stain sealers. It can also be used as a safe coating on foods, such as fruit and sweets, to give them a glossy shine.

with the grain – cutting the timber is easier and cleaner l across the grain – cutting across the grain lines but the plane of the cut is still aligned with them l end grain – the timber is cut at right angles to the grain, for example when trimming the ends of planks End grain often needs to be repaired by the decorator by stopping and filling, which should be done after priming. A stopper is stiff material used to ‘make good’ gaps and holes on surfaces and it dries with the minimum amount of shrinkage. Areas such as open joints and splits in timber need to be stopped and made flush prior to decoration.

Open joints – gaps in timber structures

There are several different types of filling methods that you will need to use. Proud filling – overfill and leave a raised amount of material filler (proud). After drying the filler will reduce or shrink back leaving it slightly proud. It will need abrading level. l Back filling – press the material deep into the area then leave it to dry. Repeat the process until the surface is level. l Flush filling – use a filling knife or caulk board to apply the filler and make the surface flush prior to applying coatings. l

Figure 19.2 Stoppers

Filler used for good open-grained timber Plastic woods – made from a mixture of resin and wood flour, used when applying clear wood finishes. Available in a ready mixed formula and two-pack formula. Very quick setting but expensive. l Two-pack stoppers – hard-wearing and can have fittings screwed into them. Dry very quickly and have little shrinkage. Must be used on bare surfaces as they can cause coatings to become defective due to the ingredients in the stopper. l Putty – substance mixed with linseed oil which becomes sticky. Commonly used on wood for filling holes and to fix glass into window frames. Less expensive than other stoppers but becomes brittle with age. l

Key term Flush – when one surface is level and even with another surface

Know how to prepare surfaces for decoration 2

Key term

Unit 2019


Moisture content Wet rot is a growth of brown fungus in damp timber. As the fungus grows, it destroys the wood. The only long-term treatment


Level 2 NVQ/SVQ Diploma Painting and Decorating 3rd edition

Find out Why should you not put iron screws into timber affected by wet rot?

of wet rot is the removal of moisture. Before working on an area affected by wet rot, you must treat it, as outlined here.

Unit 2019 Know how to prepare surfaces for decoration 2

Rake out any defective timber. Allow the surface to dry and flood the timber with a clear wood preservative. Allow it to dry and spot prime the affected areas with wood primer. l Fix wood screws (non-ferrous, that is non-iron) into the timber. l Apply a coat of two-pack polyester filler to the surface and allow it to dry. The screws will help the filler adhere to the surface. l Apply a second coat of filler and allow to dry. Abrade the filler so it is flush. An acrylic spot filler (a soft putty) may be needed to fill any minor imperfections. l

Glue residue and nail heads Glue residue is excess glue left on the surface of timber. If dry, this can be removed with a scraper and then sealed with knotting solution. If wet, remove with scraper and clean with white spirit or turps and leave to dry. Nail heads may be left projecting above the surface. Place a nail punch squarely onto the nail head, covering the whole surface of the head, and hammer the nail further into the timber until it is below the surface. Apply a stopper or filler to the hole.

Surface and physical properties of timbers and timber sheet products Tactility and aesthetics are the key characteristics of wood and timber. Tactility – how workable the timber is to create different structures and fittings. The more workable it is, the more potential uses it will have. Tactility also applies to other materials, such as plaster. l Aesthetics – the finishing look of timber when it has been stained and varnished. The more pleasant the aesthetic look, the more likely it is to be used decoratively. l

Figure 19.3 Tactility and aesthetics: the workability and beauty of timber

Porosity A porous surface is one that contains tiny holes through which liquids or gases can pass. In order to prevent porous surfaces, such as timber, from being penetrated by water or damaged by frost, a silicone water-repellent layer can be applied to waterproof the surface. When dry it is completely clear.


Unit 2019 Know how to prepare surfaces for decoration 2

Physical properties Timber has a number of physical properties. Some of these properties also apply to other materials you will encounter – the qualities they give will be essentially the same for each type of material.


Resistance to wear and tear. Also difficulty to saw or plane the timber


Amount of stress timber can resist before bending. The ‘stiffer’ the wood, the stronger it will be


Ability to expand and retract without damage


Ability to absorb shocks and damage


Ability to ‘stick’ or fix to a different surface

Figure 19.4 Silicone water repellent used on porous timber

Unit 2019

Ability to trap heat. Wood has low thermal conductivity so it is a natural insulator. Air pockets in the wood make it a barrier to heat and cold

Table 19.4 Physical properties of timber

Capillary action This is a process where liquid is drawn up through a small gap between the surfaces of two materials. In a building this could allow water to rise up from the surface and into the building. Timber can be affected by this if its moisture content is above 30 per cent. Capillary action will also cause the timber to rot. This also applies to plaster and metal areas. These will not rot but plaster will become weaker and metal will corrode (see page 111).

Appropriate abrasives Abrading a surface means wearing away the top layer by rubbing, or creating friction. This is a very important part of surface preparation. It provides a key for the coating or covering to be applied and smoothes the surface to give a good-quality finish.

Remember Abrading a new softwood or hardwood may result in damage due to scratching or furring (the lifting of wood fibres). For this reason, it is best to simply dust off the surface prior to painting.

It is important that the correct type of abrading material is used.

Key term

Abrading material that is too rough can leave scratches on surfaces that show through to the finish. l Material that is too fine can have a long preparation time and be ineffective at removing or levelling rough surface imperfections. l Cheap and inadequate materials (such as glass paper) can greatly extend the preparation time as they get blunt and clog very quickly.

Key – roughness on a surface provided to aid adhesion


Know how to prepare surfaces for decoration 2



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Abrading materials and equipment

Grades of abrasives It is important to select the correct grade of abrasive for each job to achieve the correct finish. The grade is printed on the back of abrasive paper and relates to the particles of aggregate to every square 25 mm.

Unit 2019 Know how to prepare surfaces for decoration 2

Figure 19.5 A small number of large aggregates will give a coarse abrading effect

A grade that gives a fine abrading affect will have lots of small particles. Figure 19.6 shows aggregate on a P80 grade dry abrading paper where 80 particles of aggregate will fit on to a 25 x 25 mm area.

Wet and dry abrasives Harcourt Education

Painting and These can beJ6637 used in both wet and dry conditions. A waterproof Decorating Zurich BT adhesive fixes9pt the abrasive particles to the backing, which means AW031 that the paper does not lose the particles when it gets wet – in fact, if wet and dry paper is used dry it tends to clog up.

Figure 19.6 A large number of small aggregates will give a fine abrading effect

Remember Always choose the correct type and grade of abrading material for the surface and the job.

Safety tip Abrading will create dust particles so ensure adequate ventilation of the work area and wear appropriate respiratory PPE. Some tools are equipped with a dust collection bag.


A grade that gives a coarse abrading effect will have large particles and therefore less of them. Figure 19.5 shows aggregate on a P20 grade dry abrading paper where only 20 particles of aggregate will fit on to a 25 x 25 mm area.

The aggregates used in wet and dry abrasive paper are often silicon carbide, but aluminium oxide is becoming increasingly popular. Particles of aggregate are closely grouped together and referred to as being ‘closed coated’. Water (sometimes mineral oil) can be used as a lubricant, preventing paper from becoming clogged. Wet and dry abrasive is available in grades from P80 (coarse) through to P1200 (very fine). Advantages


Extremely good for Harcourt high-quality work Education

More expensive than some dry abrasives

J6637 Painting and Decorating Wide range of grades available 9pt Zurich BT AW032 Cleans the surface as it abrades

Low dust levels

Unsuitable for bare timber Clogs up easily if used dry Surface must be dry before decoration

Table 19.5 Properties of wet and dry abrasives

Dry abrasives These use a non-waterproof adhesive to fix the abrasive particles to the backing paper. The best aggregate to use in this type of paper is aluminium oxide grit. Glass and garnet are common, but less effective.

Unit 2019 Know how to prepare surfaces for decoration 2


When worn, particle edges shear off revealing smaller but sharper edges (Figure 19.7)

Aluminium oxide can be expensive compared to other abrasives

Available in sheet, roll, disc and belt form

High dust levels produced

Aluminium oxide particles wear down and break away

Remaining particles are smaller and sharper

Figure 19.7 How aluminium oxide breaks down

Available in self-adhesive rolls – abrasive can be torn off and fixed to purpose-made rubbing blocks

Table 19.6 Properties of dry abrasives

Figure 19.8 Belt sander

Mechanical sanding Electric tools can greatly reduce time spent preparing surfaces and increase the surface area covered. Electrical sanders work by moving an abrasive pad or belt at a fast speed.

Belt, drum and orbital sanders The heavy duty sanders most commonly used by a decorator are belt, drum and orbital sanders. Belt and orbital sanders are hand-held power tools best used for sanding large, flat items of joinery. A drum sander is self-propelled and used for stripping floors. A rough grade of abrading material should first be used to remove surface coating. The surface can then be brought up to a smooth finish by progressively using finer and finer abrading material. Advantages


Effective at abrading large areas

More expensive than abrasive papers

Faster rate of abrasion than by hand

Only suitable for large, flat areas

Figure 19.9 Drum sander

Unit 2019


New abrasive

Know how to prepare surfaces for decoration 2

Aluminium oxide abrasive (production paper) is usually available ‘open coated’, where the particles of aggregate are spaced apart on the backing paper. This reduces the risk of clogging as the gaps allow waste to escape. Dry powder lubricants can be used on some types of dry abrasives, breaking away when heat is generated by the abrading process, preventing clogging of the abrasive. Dry abrasives are available in grades ranging from P20 (coarse) through to P320 (very fine).

Can create large amounts of dust

Table 19.7 Properties of belt and orbital sanders

Figure 19.10 Orbital sander


Level 2 NVQ/SVQ Diploma Painting and Decorating 3rd edition

Did you know?

Disc or rotary sanders

Small electric sanders are also available with triangular heads for use when sanding corners.

Rotary sanding involves the use of rotating discs of abrasive material and can be used to prepare small or contoured surfaces.

Abrasive discs can be fitted to electric drills and angle grinders.

Unit 2019 Know how to prepare surfaces for decoration 2 106

Figure 19.11 Disc (or rotary) sander – in this instance, an electric drill fitted with an abrasive disc attachment

Different types of abrasive disc are available: flat discs that require a backing pad l flap discs made up from flaps of abrasive, which are more expensive but also more effective l grinding discs that can be used for removing very heavy, small areas of rust. l



Do not burnish the surface

Only suited to small areas

Effective at removing isolated patches of rust

Not suited to complex surfaces (discs cannot reach into awkward corners)

Relatively low initial cost of equipment

Table 19.8 Properties of disc or rotary sanders

If the sander is equipped with a dust collection bag, make sure it is working and empty it before using the tool. After sanding, the wood dust collected should be disposed of appropriately. Sanding dust should not be left in bags indoors as there is a danger of it catching fire through its own heat.

Appropriate solvent-based and water-based primer Priming is the first coat of paint applied to a surface. Primers protect the substrate and give an even and consistent finish to the final coat. Universal primers are designed to be used on a range of surfaces. If the surface preparation or the application and choice of the primer is incorrect in any way, the durability of the paint system will be reduced. Solvent-based primers – form a waterproof layer to prevent wet rot in timber surfaces. They do not raise the grain of the wood when applied, but have a longer application time than water-based primers as the solvent content prevents them from drying as quickly as water-based primers. l Water-based primers – provide a moisture screen to the surface. Water-based primers do not soak into timber, meaning they adhere less well than oil-based paints. They are low in VOCs and odour, quick to dry and more durable on hardwoods. l


Acrylic primer

Water based. Reapplied as an undercoat to speed up coating process. Mostly used for internal timbers but can be used externally.

Aluminium wood primer

Solvent based. Has aluminium non-leafing particles to make it more suitable for priming resinous timbers such as Columbian and Oregon pines. Can be used for both internal and external timbers.

Wood primer

Solvent based. Can be used on softwood and hardwood internal and external timber surfaces.

Preservative primer

Solvent based. Used for external timbers only. Similar to wood stains and varnishes as it protects the timber

Table 19.9 Types of primer

Correct preparation process for rectifying defects in timber There are different preparation techniques for each type of timber surface. Follow the techniques described earlier in this unit, as well as remembering the different qualities of types of timber, before you begin work.

Bare untreated timber For basic painting tasks: seal any knots in timber using knotting solution l prime the surface using oil-based wood primer (for external surfaces) or acrylic primer undercoat (for internal surfaces) l fill using polyfiller and decorator’s caulk, rub down and dust off l apply one coat of undercoat, rub down and dust off l apply another coat of undercoat if necessary then apply one coat of gloss Alternatively, for staining or varnishing tasks: l

fill holes in timber with putty or coloured stopper and apply a base coat l rub down and dust off l apply one coat of wood stain or varnish and lightly rub down and dust off l apply second coat of wood stain or varnish. l

Know how to prepare surfaces for decoration 2


Unit 2019

Unit 2019 Know how to prepare surfaces for decoration 2


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Previously painted timber Rub down using sandpaper. If necessary, fill using polyfiller or caulk. l Apply one coat of undercoat, rub down undercoat and dust off. l Apply one coat of gloss. l

Rough cut timber Rough sawn timber should be dry brushed thoroughly to remove soil, vegetation and dust. Apply one coat of timber preservative or wood stain. l Apply a second coat of timber preservative or wood stain. l

Unit 2019 Know how to prepare surfaces for decoration 2 108

K2. Preparing metal surfaces ready to receive finishing systems Key term Element – a substance that cannot be broken down into any other substance. For example water is not an element as it can be broken down into hydrogen and oxygen. These cannot be broken down so are elements

Metal has a wide range of uses throughout buildings and structures. It can be used for frames, girders and trusses. Some metals, such as aluminium, are also used for decorative reasons. There are several different types of metal that you may encounter as you work. Metals are either pure or alloys. Pure – the metal is made from only one element. Common examples of this include gold, silver, lead, copper, aluminium, zinc, iron and tin. l Alloy – a mixture of two or more metal elements, used when a strong, light metal with properties that do not exist in a pure metal is needed. Aluminium alloy is a common example of this. l

Surface and physical properties of metal types Metal shares some qualities with timber, including porosity (page 102). The other key qualities of different types of metal are shown on page 109. Metals will not exhibit all these qualities.

Unit 2019 Know how to prepare surfaces for decoration 2


Can be hammered and pressed into different shapes


Has the ability to conduct heat and electricity


Can regain its shape after being misshapen during use


Resistant to scratches and cuts during construction


Extremely hard but can be broken very easily


Can be stretched without breaking and turned into a fine wire. Metals with this quality are used for metal cables.


Can absorb shock and energy without breaking (the opposite of brittleness)

Tensile strength

Tested under extreme conditions (pulling, squashing, twisting and shearing) and can withstand these forces


Denseness of the metal in relation to its size


Tested to withstand heavy loads without breaking

Table 19.10 Key qualities of different types of metals

Types of metal and their applications

Non-ferrous metals Non-ferrous metals do not contain iron and are not magnetic. They are usually more resistant to corrosion as they have non-friable oxide layers, created by the atmosphere. These should be dry and free from grease prior to painting. Previously painted non-ferrous metals need to be abraded and any corrosion deposits found should be scraped back to a firm edge where any flaking paint is evident.

Ferrous metals Ferrous metals contain iron and may have small amounts of other metals and elements added to them to give them the properties they need. Most ferrous metals are magnetic. These surfaces are prone to rusting and will need to be cleared of all rust prior to painting. Depending upon the extent of the rust, it can be removed with the use of a wire brush, mechanical wire brush, abrasive papers and/or scrapers.

Find out Use the Internet as well as materials lists and manufacturers’ information to find out more about the circumstances where these qualities of metals are particularly desirable.

Unit 2019


Know how to prepare surfaces for decoration 2



Level 2 NVQ/SVQ Diploma Painting and Decorating 3rd edition



Unit 2019 Know how to prepare surfaces for decoration 2



Copper (non-ferrous)

Extremely ductile, malleable, good conductor. Tarnishes and oxidises quickly. Easily damaged and must be stored carefully.

Available in tubes, sheet, wire, rod and flat bar. Used for water pipes, electrical wiring and roofing.

Aluminium (non-ferrous)

Extremely malleable, ductile, lightweight and conductive. Non-toxic and often alloyed. Highly resistant to corrosion. Can be dyed (anodising).

Some types of window frames. Excellent for stamping and forming.

Lead (non-ferrous)

Very soft, malleable, heavy and highly resistant to corrosion. Tarnishes to a dull grey when exposed to air. Very poor conductivity. Poisonous, so care must be taken.


Galvanised steel (ferrous)

Highly resistant to corrosion, as alloyed with zinc to protect the iron. Can withstand saltwater, moisture, rain, snow, etc. Lightweight, fire-resistant, basically maintenance free and extremely durable and resistant to scratches and abrasion.

Girders, frames, roofing, support beams, piping, etc. Available in tubes, sheets, ropes and flat bar.

Cast iron (ferrous)

Corroding metal, non-toxic, made by melting pig iron and small amounts of scrap steel. Strong, hard, self-lubricating and brittle but also cheap, well wearing and sustains heat.

Bridges, buildings, stairs, handrails, cast iron columns, items such as machinery parts

Wrought iron (ferrous)

Iron alloy with very low carbon content made by melting porous iron with slag and other impurities. Gives it properties not found in any metal. Tough, malleable and ductile. Can crack if bent or heated up and brittle when cold. Has a rough texture so it can hold platings and coatings.

Roof trusses, ornamental ironwork, pipe work, handrails. Available in bar form, sheets, rods and hoops.

Mild sheet/ steel (ferrous)

Iron alloy, corrodes and has high carbon content so vulnerable to rust. Malleable, ductile and tough with high tensile strength and bends easily.

Girders, tubes, screws, nuts and bolts and garage doors (use composites for wood apppearance).

Table 19.11 Non-ferrous and ferrous metals


Unit 2019 Know how to prepare surfaces for decoration 2

Main corrosion factors Corrosion is the destructive attack on a metal from its environment. The main corrosion factors are all found in the atmosphere. They are: oxygen l hydrogen l moisture l pollutants. The most common form of corrosion is oxidation. The atoms in metal combine with the atoms in oxygen to form oxides. Iron rust is the most recognisable form of corrosion and is caused by iron oxide appearing on iron or steel components. Metals with high iron content will corrode more than metals with low iron content. Metals which show signs of corrosion, such as pitting, must be repaired and the metal protected with a coating. l

Corrosion can protect some metals, such as copper. Copper is used as both a pure metal and an alloying material. Because it is very resistant to corrosion, it does not need to be treated with protective coatings as most other metals do. It develops a protective oxide coating. This thickens the copper and turns it green.

Galvanic corrosion and cathodic protection Electrolysis is an electrochemical process, where a metal comes into contact with an electrolyte (a conductor, usually water) and parts of the atoms of the metal (electrons) flow from the metal into the electrolyte, causing it to corrode. This is called the galvanic action. If two metals are in the same environment, the metal that has less resistance to electrolysis (the anode) will corrode before the other metal (the cathode). Some metal coatings have metal in them lower than the actual substrate being painted. This provides protection to the substrate, as the anode in the coating causes it to corrode first. This is known as cathodic protection.

Anodising – an electrochemical process that converts metal surfaces into a decorative, durable, corrosiveresistant, anodic oxide finish. Aluminium is the metal often used, but titanium and magnesium can also be used. These metals are immersed in an acid electrolyte bath with an electric current running through the medium Pitting – formation of small pits in a metal surface as a result of corrosion. Crevice corrosion occurs where nuts, bolts and gaskets have been used

Did you know? On iron and steel a thin, flaky black iron oxide called millscale can form (see page 113). This is an example of cathodic protection to the steel.

Find out

Unit 2019

During your inspection of the work surface, you may notice areas where the surface has corroded, usually due to rust. This will have to be cleaned and removed before work can be carried out.

Key terms

Know how to prepare surfaces for decoration 2


Use the Internet and other resources to try and find some examples where electrolytic corrosion is used.


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To use an example from Table 19.12, if iron sheet has a zinc coating, this will protect the iron as the zinc will rust first. The zinc is less resistant than the iron and therefore is the anode. Copper Tin Lead Nickel Iron Zinc Aluminium

Unit 2019 Know how to prepare surfaces for decoration 2


Table 19.12 Metals in order of their resistance to corrosion

Appropriate primers and their function Primer


Mordant solution

Also known as etch primer or T-wash. Very toxic and used for non-ferrous metals. Must have an overcoat after application to avoid deterioration. Available in two-pack coatings, which have better stability and adhesion but a limited shelf life once mixed. Touch dry within 1–4 hours and can be recoated in 10 to 14 hours.

Metal primer (acrylic-based)

Specially formulated to prevent rust and provide adhesion, low VOCs, non-toxic, odourless. Expensive to purchase and can only be used on properly prepared surfaces. Can be recoated in 4 to 6 hours.

Zinc phosphate

Solvent-based primer with a rust-inhibitive pigment, touch-dry within to 3 hours. Suitable for non-ferrous metals, iron, steel and blast-cleaned surfaces.

Key term Blast cleaning – an alternative way to remove corrosion and coatings from steel or metal work. It involves grit particles being shot through a hose under high air pressure, which removes everything it hits on surfaces. This method is used in heavy industry and in fabrication shops.

Table 19.13 Primers and their functions

Preparation processes for metal Solvent wiping Solvents (for example, white spirit and turps) remove grease and oil from metal prior to decoration. Solvents are used to avoid rust on the surface. Solvents are very toxic so make sure you are in a well-ventilated area and that you are wearing the correct PPE.


Unit 2019 Know how to prepare surfaces for decoration 2

Removing rust by hand Cleaning off rust by hand is normally done when repainting rusty steelwork, as it is usually the cheapest method. The problem with hand cleaning is that the use of scrapers, chipping hammers, wire brushes and abrasives will not remove all traces of rust. In addition, the overuse of a wire brush can serve only to polish the rust on the surface, affecting the ability of the primer to adhere to the surface. Follow this procedure when cleaning by hand. Remove any traces of oil or grease to avoid spreading it around the surface. l Scrape off all loose rust, millscale and previous coatings. l Use a chipping hammer around rusted nails, bolts and rivets. l Use a wire brush to remove loose rust, but avoid burnishing. l Finish off by abrading with a rough aluminium oxide abrasive – P40–P60 (see page 104–106).

Figure 19.12 A wire brush can be used to remove loose rust

Millscale – a thin flakey black iron oxide formed on iron and steel. It is also a cathodic protection to the steel Burnishing – polishing

Power tool cleaning is generally quicker and more effective than hand cleaning and will extend the life of the paint system. Loose rust, millscale and the existing surface coating can be removed using power wire brushes, grinders and needle guns, although some millscale will not be removed even with power tools. Again, care should be taken not to over-polish the surface or the adhesion of the primer will be negatively affected. Follow this procedure when cleaning with a power tool. Remove any traces of oil or grease from the surface. l Scrape off all loose rust, millscale and previous coatings. l Use a needle gun to remove rust around corroded nuts, bolts and rivets, etc. l Select the most effective method of removing rust to suit the nature and condition of the surface (for example, rotary wire brush, disc sander or angle grinder). l


Figure 19.13 Power tools such as needle guns and angle grinders can be used to remove rust from surfaces

Know how to prepare surfaces for decoration 2

Removing rust with power tools

Key terms

Unit 2019


Dry abrade using emery paper or a scraper and wire brush, and dust off. l Apply good general purpose metal primer or zinc phosphate to areas where rust has been removed (apply a full coat for previously painted steelwork). l Apply undercoat. l Lightly abrade, dust off and apply a gloss coating. l


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Key term

Other metal surfaces

Bitumen – a heavy, semi-solid, brown-black substance created as a result of the oil refining process (also known as asphalt or tar)

Ferrous metals (iron and steel)

Unit 2019 Know how to prepare surfaces for decoration 2

Non-ferrous metals (aluminium, copper, zinc, brass etc.) Degrease surface with white spirit. l Galvanised and zinc-sprayed surfaces should be treated with mordant solution. l Etch the surface with wet and dry abrasive paper and white spirit to provide a key. l Apply one coat of metal primer or universal primer. l

Working life Jamila has given a client an estimate for repairs to discoloured, flaky and rusty metal railings. She states that the railings can either be removed and abrasive blasted, then treated and a full paint system applied or they can be prepared by hand and spot primed before a paint system is applied to them. There is a cost difference between the two because of the timescales involved. Which system should be chosen? What has caused the deterioration of the metal railings? How would the metal be treated after being blast cleaned? What suitable paint system could be used? Which estimate should the client go ahead with?

K3. Preparing trowelled finishes and plasterboard ready to receive finishing systems Did you know? Plasterboard can also offer extra moisture protection as it has moisture controlling and water-resistant properties.


Remove all corrosion and millscale via mechanical means. l Degrease with white spirit if necessary. l Allow the surface to dry thoroughly and apply primer with a brush. l Bitumen-coated surfaces will require sealing with shellac knotting solution or aluminium primer. l Four coats of paint will be required to achieve adequate film thickness (as recommended by the British Iron and Steel Association). l

Plasterboard is a durable and high-quality lining for walls and ceilings, lift shafts and stairwells, corridors and auditoriums. Trowelled finishes are surfaces constructed from bricks and blocks. Most walls use bricks and blocks as a central part of their construction.

Key term


Gypsum – a white rock produced as the by-product of industrial processes

Most plasterboard is made from gypsum, processed into a board and given a paper covering. Standard plasterboard is suitable for most applications and is compatible with direct decoration or plaster finishes. It has a grey facing and an ivory coloured back. Plasterboard is used in a range of residential and commercial buildings. Dry lining is where dividing walls in a building are made from plasterboards (square and feather-edged) which are attached to timber structures (stud walls) and taped up. The joints of the two boards are sealed with joint tape with the joint then plastered over for a smooth finish.

Blockwork Concrete blocks are heavy but produce strong finished work. They are used where a lot of weight will be put on top of, or against, the wall. They are also used to form footings below ground on walls that support steel. Lightweight blocks are lighter versions of concrete blocks, produced in response to health and safety restrictions on lifting and handling units heavier than 20 kg. Block



Solid block

Concrete block used for making walls above ground for commercial, industrial and leisure buildings. Also used for beam and pot floors.

Hollow block

Concrete block used where reinforcement is needed. Same finish as solid blocks but with hollow sections running through them. Filled with vertical reinforcement rods and concrete, making them very strong.

Aircrete block

Lightweight block made of a microcellular composition (aircrete). Lightweight but very durable. Used for foundations, beam and block floors and internal and external cavity walls.

Figure 19.14 Plasterboard

Know how to prepare surfaces for decoration 2

Types of surface and applications

Unit 2019

Unit 2019 Know how to prepare surfaces for decoration 2

Table 19.14 Types of blocks and their uses


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Brickwork 65 mm




.5 m


er etch




Figure 19.15 Sizes of brick, header and stretcher

Bricks are smaller than blocks and so more are required per square metre. A brick is 215 mm long, or half the length of a block, and 65 mm high. The length of a brick is called the stretcher and the end of a brick is called the header. Like blocks, bricks are held in place by mortar, a mixture of sand, and water used for bedding and jointing. Bricks, like Client:cement Harcourt Job No: J6598 Fig No: AW078 blocks, need to be laid level and straight with equally sized joints to achieve a sound wall with a good appearance.

Unit 2019 Know how to prepare surfaces for decoration 2

Physical properties of plaster and trowel surfaces Plaster, brickwork and blockwork share a number of physical properties with metal and timber. Plaster has qualities of capillarity, tacility, adhesion and porosity. Brickwork has qualities of capillarity and porosity. Key terms Alkaline – having a pH greater than 7 (an acid has a pH of less than 7) Saponification – a chemical reaction that makes soap and so foams up as a result Permeable – allowing things to pass through

Acrylic coating

Alkali surface Alkalinity permeating coating

Figure 19.16 Alkalinity permeating through an acrylic coating




Found in some surfaces and can cause defects if the surface has not been prepared and primed correctly


Refers to plaster being able to bond to surfaces without reacting or causing defects

Soluble salt content

Salt found in brickwork. It must be removed correctly or will keep returning and lead to efflorescence (see page 117)

Table 19.15 Some physical properties of plaster, bricks and blocks

Alkalinity The chemical nature of surfaces such as concrete, cement rendering, asbestos sheeting and some plasters is alkaline. This can cause problems if a solvent-based paint is applied as the alkalinity in the surface can attack the paint, causing saponification. To prevent this, you should apply an alkali-resistant primer. This forms a barrier between the surface and the paint. The permeable nature of acrylic surface coatings means they need an alkali-resistant primer to prevent alkalinity coming through if the surface becomes damp.

Harcourt Education J6637 Painting and Decorating 9pt Zurich BT AW034


Unit 2019 Know how to prepare surfaces for decoration 2

Defects associated with plaster and trowel work Like timber, plaster and trowel work can suffer from cracks, nail heads and open joints. Moisture must also be removed from plaster and trowel surfaces to avoid mould growth and many of the defects covered below. Figure 19.17 Settlement cracks

Unit 2019

Settlement cracks appear in plaster and cement work in floors and ceilings. They are caused by shifts in the elevation of a structure caused by shifts in the soil. The soil may not have been compacted properly before construction and, as it decays, collapses – leaving a void beneath the building. Shrinkage is caused by material drying out after completion and cracking as it shrinks. In cement, if too much water is added to the mix then it can shrink once this water has evaporated. Plaster that has been properly adhered will avoid shrinkage.

Efflorescence Efflorescence can be seen as the white patches on cement-based surfaces and it can occur on brickwork and plaster. Because cement is porous, moisture can penetrate it, dissolving some of the lime and creating calcium hydroxide. This then rises to the surface when the cement dries out, leaving white patches of calcium carbonate. Efflorescence will have to be removed before decoration. Scrub the surface with a stiff fibre brush or a wire brush. Never remove efflorescence by washing the surface as the calcium carbonate will dissolve in the water and sink back into the cement.

Defective rendering and raking out Rendering is a coating of plaster applied to stonework. Cracks can form in this. To repair small cracks:

Figure 19.18 Efflorescence

Know how to prepare surfaces for decoration 2

Settlement cracks, shrinkage and dry out

scrape away any loose coatings and particles of masonry l apply filling agent – exterior grade filler (polyfiller type) could be used but this would probably re-crack after a short period of time, whereas exterior acrylic caulking will provide more permanent flexible repair. l


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Repairing a large crack in rendering The crack must be undercut to give the mortar holding power

Unit 2019 Know how to prepare surfaces for decoration 2 118

Step 2: Undercut the crack.

Step 1: Rake out any loose coatings and rendering using a 25 mm scraper or pointing trowel.

Step 3: Fill the crack with a sand and cement mortar to a ratio of one part cement to three parts soft sand. This is known as ‘pointing up’.

Harcourt Education J6637 Painting and Decorating When 9pt dry theBTmortar Zurich AW040

can be painted over, but this repair would probably re-crack after a short period of time.

Harcourt Education J6637 Painting and Decorating 9pt Zurich BT AW042

Alternatively, rake out, undercut and fill as above and then allow to dry. Apply a bituminous caulking compound over the crack and bed a nylon type bandage over the length of the crack. Further applications of the caulking compound can then be made over the bandage to provide an invisible reinforced repair, which will last longer.

Popping Remember If a hole or crack on a surface is not filled proud it can shrink when drying and will need filling all over again.

Popping occurs when movement causes plaster to break away from plaster nail heads. To rectify: dry scrape and dust off l spot prime the nail head and apply the correct filling agent proud l when the filler is dry, rub down to leave an even surface and apply a coating. l

Unit 2019 Know how to prepare surfaces for decoration 2

Processes for rectifying surface defects Figure 19.19 Scraping knife

When removing wall coverings from plasterboard wet in first. Apply water to the wallpapered area after first scoring the paper. This water penetrates the paper making it softer and easier to remove. You can also wet in holes and cracks in rendering before applying filler to prevent it drying out before it sets.

Scraping Scrapers can be used for many different tasks such as removal of wallpaper, rust, nibs from plaster surfaces and flaking paint and pastes. Defects must be scraped off before you can begin painting.


Figure 19.20 Caulking with a mastic gun

Caulk is a waterproof filler and sealant used in cracks and gaps. Mastic is an acrylic type of caulk and is applied using a mastic gun, which is a frame that holds and helps dispense mastic from its tube. When it is dry, mastic feels a bit like rubber. Surplus caulk can be removed with a filling knife. Any remaining material can then be sponged off. Figure 19.21 shows two examples of how caulking can be applied to the tops of skirting boards. The illustration on the left shows the caulk applied correctly. The illustration on the right shows incorrect application.

Appropriate primers for trowelled finishes and plasterboard



Figure 19.21 Correct and incorrect caulking




When used as a primer it is thinned down with water and used on porous surfaces. Also used to seal plasterboard before applying further coatings as it helps to stop coatings being absorbed.

Primer sealer

Solvent based with good alkali resisting properties designed to seal porous, dry and friable surfaces and touch dry within 8–12 hours. Cannot be recoated until 16–24 hours later and should not be thinned to stop loss of properties. Can also be used to seal defects.

Alkali-resisting primer (ARP)

Solvent based and specially designed for surfaces that are alkaline and require a solvent-based finish. New, dry interior plaster and masonry finishes best primed with this coating. Touch dry after 8 to 12 hours and re-coatable after 16 to 24 hours.

Unit 2019

Wetting in

Know how to prepare surfaces for decoration 2

Some of the processes for rectifying surface defects have been covered earlier in this unit; abrading (page 103), filling (page 101) and degreasing (page 112).

Table 19.16 Primers and their uses


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Did you know? Newly plastered walls can be painted with emulsion because it allows the wall to ‘breathe’.

Preparing surfaces according to finish required Plaster

Untreated plasterboard Apply one coat of emulsion thinned by up to 10 per cent. l If necessary, fill using polyfiller then lightly rub down and dust off. l Apply one coat of emulsion as an undercoat, rub down and dust off. l Apply second coat of emulsion. l

Unit 2019 Know how to prepare surfaces for decoration 2 120

Bare plaster Dry scrape with a scraper or broad knife. l Apply one coat of alkali-resisting primer or one coat of emulsion thinned by up to 20 per cent. l Fill any holes or dents using polyfiller then rub down using sandpaper and dust off. l Apply first coat (eggshell or emulsion), rub down and dust off. l Apply second coat of paint (eggshell or emulsion). l

Did you know? The reason the first layer of primer applied to masonry should be applied with a brush is because the action of brushing forces the paint into the surface.

Previously painted plaster Wash down using sugar soap solution. l Fill holes or cracks using polyfiller and decorator’s caulk then rub down and dust off. l Apply first coat (eggshell or emulsion), rub down and dust off. l Apply second coat of paint (eggshell or emulsion). l

Masonry Clean the surface with a jet wash or scrub with a suitable detergent, remove loose materials and treat any efflorescence. l Any mould should be treated with a sterilisation wash, also known as fungicidal wash, before being removed with a scraper. The surface should then be re-treated with the sterilisation wash. l Ensure surface is completely dry before applying any coating. l Prime new masonry and older or weathered masonry with stabilising solution or all-purpose primer, applying with a brush. Previously painted surfaces in good condition may not need priming. Subsequent coatings can be applied by brush, roller or spray. l

Functional skills

Alice is working on a barn conversion with an apprentice, Michael. The client wants the outside painted cream and brown. Because of time pressure, Alice tells Michael to start applying cream emulsion straight onto the walls while she applies brown emulsion to the woodwork.

In answering the questions in this section you are practising the functional skills required to read different texts and take appropriate action, e.g. respond to advice/instructions, FE 1.2.1 – 1.2.3 This may also involve giving oral answers to questions from you tutor and is practice for speaking and listening – FE 1.1.1 – 1.1.4

Should Michael do this? What paint system should be used? What defects will occur if the paint system is not right? What should be done first to any of the surfaces? What paint system could be used on this project?

K4. Removing previously applied paint and paper ready to receive finishing systems If the surface you are working on already has a coating of paint that is in poor condition (for example, it has a brittle paint film or paint actually flaking off), it will be necessary to remove the entire coating in order to produce a good finished effect.

Paint and paper defects that need to be removed Some of the defects that can lead to paint and paper being removed have been covered earlier in this unit. Information about peeling paper from plasterwork can be found on page 119. The following defects must be removed prior to redecoration to prevent them showing through new coatings and coverings. Defect



Blisters on wallpaper are caused by trapped air. Blistering on paint is caused by trapped moisture or by painting on hot surfaces.

Cracking or crazing

Paint film which has become thick with layers of paint can become excessively hard and brittle with age, causing cracks. To rectify fully prepare the surface and abrade.

Excessive film thickness

Caused by applying too much paint to a surface, spoiling the final appearance. A liquid paint stripper or blast cleaning will be needed to remove.


Caused by lack of adhesive on wallpapers or wear and tear on painted surfaces.

Communicating effectively is an essential skill in everyday work. You may be expected to take part in discussions about your work and asked for your opinions.

Remember You will need to protect the work area before beginning work – turn to Unit 2020, pages 134–137 for more information on protecting the work area.

Know how to prepare surfaces for decoration 2

Working life

Unit 2019

Unit 2019 Know how to prepare surfaces for decoration 2

Table 19.17 Defects that must be removed before redecorating


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Figure 19.22 Flaking

Flaking is caused by paint film splitting, causing hairline cracks to appear in the paint, which in turn leads to the flaking of paint chips from the surface. It can be caused by the coating being either over thinned or spread too thinly over the surface. To rectify this problem, remove the loose or flaking coating with a scraper or wire brush then abrade the area affected. You will need to prime any bare spots then repaint again.


Unit 2019 Know how to prepare surfaces for decoration 2

Mould is a furry growth of micro-organisms (a fungus) that grows in moist or warm conditions. If mould is found, all traces of it must be totally removed to prevent it re-establishing underneath an applied coating. The following procedures should be followed to remove mould growth. Figure 19.23 Mould growth

Safety tip Fungicidal washes are poisons and should be treated with extreme care. PPE must be worn at all times – rubber gloves, goggles and suitable overalls. After using this type of product, make sure that you wash your hands before eating or touching food.

l l l

Wet the mould to avoid the spread of spores to other areas. Remove heavy patches of mould with a scraper or wire brush. Apply a fungicidal wash to the affected area and allow it to dry. If possible, the affected area should be left for a week and re-treated if the mould reappears. In most cases, only one application will be necessary. This is because fungicidal wash has a residue effect on the surface, which means that traces of it remain, continually removing mould growth from the surface, sometimes for many years.


Removing paint from substrates and safety precautions when doing so There are different methods that can be used to remove paint from substrates before any redecoration or applying of new coats. You will need to be aware of a number of safety issues when using these methods.

Decontaminating surfaces following use of liquid paint removers After using liquid paint removers you need to remove all traces of it by washing the area down with warm water and detergent before flushing the surface with clean water. This will prevent damage occurring to other surfaces, as well as accidents such as burns. Any residue of the liquid paint remover will also react with future coatings.


Unit 2019 Know how to prepare surfaces for decoration 2

Did you know?

Removing paint by burning it off with heat, using either an LPG (liquefied petroleum gas) burning off torch or a hot air stripper, is the fastest method of removing coatings from timber surfaces.

Some local authorities have banned the use of LPG strippers in favour of hot air strippers. This is because there is a reduced risk of fire and damage to property.



Fast and efficient method of removing thick layers of paint

Many local authorities have banned LPG because of fire risks

Can be used when there is no electrical supply

Danger of cracking glass in windows when working around frames

Low running costs

Scorches timber easily.

Table 19.18 Advantages and disadvantages of using an LPG burning off torch

Some important safety notes when using an LPG burning off torch When starting up, check the hose and fittings for gas leaks using a solution of detergent and water. l Ensure a fire extinguisher is nearby. l Avoid burning off any timber adjacent to the roof structure of a building, as there is the risk of igniting any birds’ nests or denatured timber. You should also remove all curtains and furnishings when burning off around window frames. l Always cease burning off operations at least one hour before you leave site and always carry out a final check for smouldering timber just before you go. l Make sure the area is well ventilated to allow any smoke or fumes to escape. l

Hot air strippers Whereas an LPG burning off torch uses a naked flame, a hot air stripper, as the name suggests, uses hot air to heat the paint, which can then be scraped off.

Removing paint with chemicals Both water-based and solvent-based chemical paint removers soften the paint coating, which can then be removed using hand tools such as shave hooks and scrapers.

Water-based paint remover Water-based paint remover is the one most commonly used in the trade and is available in a gel form.

Figure 19.24 LPG burning off torch

Figure 19.25 Hot air stripper

Safety tip Paint fumes give off toxic gases when burned so make sure you are wearing the correct PPE.

Know how to prepare surfaces for decoration 2

LPG burning off torch

Unit 2019

Removing paint with heat

Safety tip Always wear the appropriate PPE when using chemical paint remover (gloves and goggles).


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Safety tip



As with hot work, make sure you conduct a risk assessment and be aware of the risk of burns and scalding from the steam and hot air.

Used as an alternative to burning off in areas where fire risk is high

All traces must be removed before scraping off the paint to avoid damaging future coatings

Doesn’t scorch or damage the surface

Slow, messy and expensive

Can be used on most types of paint

Can soften some plastic surfaces Can raise the grain of timber Chemicals and fumes can be harmful to health

Table 19.19 Advantages and disadvantages of water-based paint remover

Solvent-based paint remover

Unit 2019 Know how to prepare surfaces for decoration 2

This is very good at removing thick layers of paint (up to 3 mm thick) from many different types of surface such as fibrous plaster, timber, stone, marble, brick and cast iron. The paste should be applied thickly to the surface (between 3 and 6 mm thick) with a trowel or filling knife. It can then be covered with cling film or greaseproof paper to prevent the solvents from evaporating and improve their action (sometimes referred to as a poultice). The paint remover can be left to act on the surface for periods ranging from two hours to five days, depending on the type and thickness of the coating being removed: l l l l

thin layers of paint – two to three hours thick layers of paint – overnight very thick layers of paint – two or more days ornamental mouldings may have to be left for up to five days.



Same as for water-based paint remover

Expensive and time-consuming

If left for correct period of time, no scraping is necessary and the paint remover can be washed off, making it ideal for delicate surfaces that cannot be scraped

All traces must be removed from the surface and the surface neutralised with water or white spirits to stop chemicals from continuing to work

Table 19.20 Advantages and disadvantages of solvent-based paint remover

Steam stripper Using a steam stripper is a very efficient way of removing surface coverings from both walls and ceilings. Care must be taken when using this method as over-application of the steam process can result in damage to the covered surface, leading to blistering and/or removal of small areas of plaster finishes. Figure 19.26 Steam stripper


Unit 2019 Know how to prepare surfaces for decoration 2

Working with pre-painted and pre-papered surfaces Pre-painted surfaces Before painting over an already painted surface, you should carry out a simple test to find out how well the old layer of paint is adhered to the surface. If it is not strongly adhered to the surface, there is little point painting over it as your finish will not last very long. The ‘scratch test’ can be performed on most surfaces as part of the preparation process.

Safety tip If hand soaking wallpapers for removal, you must use rubber gloves or gauntlets, similar to when washing down. You will also need to make sure that any electricity in the room is turned off, in order to avoid the risk of electrocution.

Step 2: Cover the scratches with a piece of masking tape, pressing down firmly. Quickly rip the tape from the surface. The adhesion of the paint is poor if it comes off on the masking tape.

Pre-papered surfaces When removing wallpapers from surfaces you may come across both vinyl papers and embossed papers that have been painted over. To remove vinyl wallpaper, peel away the vinyl film from the backing paper. This usually comes off in large strips. Then you can either leave the backing paper on the surface as a lining paper or remove it by soaking and stripping it with a scraper.

Know how to prepare surfaces for decoration 2

Step 1: Use a sharp trimming knife to make a few cuts in one direction and a few cuts in the opposite direction

Unit 2019

The scratch test

There should be a starting point for soaking wallpaper. It is best to soak the paper a few times before scraping, as the longer the soaking time, the easier it is to remove the paper. If there is a starting point, this will allow the last area where water is applied to soak sufficiently – meaning all the areas have had the same soaking time. This will speed up the task.

Figure 19.27 Removing wallpaper


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Removing painted wallpapers is more time-consuming because the paper has a coat of paint. Score the paper then apply water in stages until the paper becomes soft enough to remove with scrapers.

Stripping paper infected with mould If wallpaper is infected with mould, you must remove these deposits. Soak the area with a mould solution or use household bleach (one part) mixed with water (up to six parts). Scrape off the contaminated paper then apply an anti-mould solution to the area before redecorating.

Unit 2019 Know how to prepare surfaces for decoration 2

Storing painting tools and equipment Some of the storage issues for paint tools and equipment were covered in Unit 1001, pages 12–15. More information on brushes and rollers can also be found in Unit 2020, page 137. Electric hot air guns and steam strippers should be stored in cases in a lockable dry storage area. Other equipment, such as metal containers and non-combustible panels, should be stored at a low level in a suitable storage area. Other storage issues: Abrasive papers – store in packets on shelves with their grade clearly identified. Keep them away from excessive heat as this makes them brittle. l Dust sheets – store on shelving and folded neatly. Must be stored dry to avoid mildew and rot. l

K5. Rectifying surface conditions Figure 19.28 Correct storage of a variety of tools and equipment

Moss and lichen

Key term Spall – when brickwork breaks up, flakes and becomes pitted


Throughout this unit we have looked at some of the common surface conditions you will come across when working as a painter and decorator. This section looks at some additional conditions, defects and rectification processes which you may encounter. This is a form of algae usually found on brick, stone and block walls. It spoils the appearance of surfaces and damages their structure, for example loosening mortar and causing brickwork to spall. To rectify, apply a moss and algae killer to the infected area. Leave this in place for the recommended time (usually about 30 to 60 minutes). Then wash the area down to remove the dead growth and treat with a suitable moss and algae prevention solution to prevent the spores from returning.

Unit 2019 Know how to prepare surfaces for decoration 2

Paint is removed along with the crumbly parts of the surface

Rectification processes and defects Many of the common rectification processes are covered elsewhere in this book including scraping (page 119), abrading (page 103), brushing (page 113), washing down for a finish (page 128) and face putty (below).

Chalking and powdering

Figure 19.29 Paint applied to a friable surface

Safety tip If you are working on a bonded asbestos surface, make sure you take precautions and wear the correct PPE, for example, gloves and a face mask.

This is a fine powder created on a coating by weathering. Heavy chalking leads to film erosion and is caused by low grade, highly pigmented paints or by using interior paints on exterior surfaces. Remove chalk by scrubbing with a stiff bristle brush, or using a power washer, and then rinse the area.

Wrinkling or shrivelling This is a rough, crinkled paint surface caused by contaminated surfaces, previous coatings that have not dried correctly, hot conditions or exposure to rain, dew, fog or high humidity before drying. To rectify, scrape or sand the substrate then recoat the surface, making sure conditions are correct and each coat dries fully.

Defective putty When removing old paint from window frames, some of the putty is likely to break away. After surface preparations have been completed, the bare timber can be primed and any defective putty replaced with linseed oil putty. Any old putty that has not broken away will be firmly adhered to the window frame and will not need to be replaced. However any gaps between the old putty and the glass must be completely sealed by forcing in linseed oil putty using a putty knife.


Linseed oil putty

Ha J6 De 9p AW

Unit 2019

A friable surface crumbles away easily when you rub your hand over it. Examples of this kind of surface include weathered cement rendering or old, spalled brickwork. Paint applied to these surfaces will also crumble off. A stabilising solution can be applied. Brush the surface down with a stiff brush to remove loose particles. Then apply the solution, which soaks deep into the surface acting like a glue, binding it down.

Know how to prepare surfaces for decoration 2

Friable surfaces

Defective putty


Figure 19.30 Defective putty


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Other surface conditions Surface condition



Unit 2019 Know how to prepare surfaces for decoration 2


Coatings applied on contaminated surfaces, which prevent adhesion. Allow paint to dry before using wet and dry abrasive paper to abrade the surface. Wash down with warm water and detergent then rinse.


Small particles of dirt on a wet coating. Abrade the surface then dust down and remove dirt before repainting.

Runs, sags and curtains

Too much coating applied to a surface and paint running down. Do not overload brush and spread out coating.

Table 19.21 Surface defects and causes Did you know?

Cleaning surfaces

When washing a surface, you should always start at the bottom and work upwards. This avoids streaking of painted surfaces, which can damage the finish.

When washing down a surface, it is very important that the correct washing agent is used. Dirt can be removed with sugar soap or a mild detergent. Oily and greasy marks will probably only come off with the use of white spirit or turps applied with a cloth or brush. Wax polish will need to be washed off with a suitable solvent or warm water and sugar soap. You may also find that smoke needs to be removed from surfaces. Make sure that the area is thoroughly rinsed after cleaning and allowed to dry completely. When cleaning a surface you will need to know what the surface coating is. Wipe the surface using a clean rag with a stain remover. If the rag is still clean, the surface is solvent based. If it is dirty, the surface is water based.


Unit 2019 Know how to prepare surfaces for decoration 2

K6. Repairing and making good surfaces

Wet, unseasoned timber or wet, newly plastered or washed walls must be given an adequate drying out period. Applying any surface coating before drying could lead to blistering, peeling, discoloration and staining. Decorating in cold conditions (below 5°C) or wet weather can result in: failure of water-based paints to dry (due to lack of adhesion) l washing off of water-based paints l blooming of alkyd finishes (for example, loss of gloss and a cloudy surface) l rain pitting of alkyd finishes l peeling. l

Know how to prepare surfaces for decoration 2

It is pointless to prepare and paint a surface if it is damp or if weather conditions are wet or very cold as this will affect the paint finish or its ability to dry. These are environmental considerations and must be taken into account during surface preparation.

Unit 2019

This unit has discussed how the different types of surfaces – timber, brickwork, blockwork, plaster, cement and plasterboard – can be affected by defects, and the methods of correcting these defects.


Level 2 NVQ/SVQ Diploma Painting and Decorating 3rd edition

FAQ Can I use caulk to fill holes in surfaces? No! It is not advisable to use caulk to fill holes and cracks because you cannot abrade caulk when it dries. This is because its flexible properties do not let it harden off. Caulk is only recommended for filling the tops of skirting board and around architrave to seal any gaps.

Unit 2019 Know how to prepare surfaces for decoration 2

How long do you leave a steam stripper on a surface when removing wall coverings? It depends on how many layers of wallpaper are on the surface. However, you should not allow the steam stripper to stay in any one place too long as you can cause the plaster on the surface to ‘blow’. This is when the plaster lifts off the surface therefore creating a much bigger defect that needs repairing.

You ‘wet in’ before applying fillers to holes and cracks to help with the adhesion of the filler and to remove any excess dust and debris that has not been fully removed during the preparation stage. When removing rust and millscale from metal, is it not better to make sure that you totally remove all traces and make the surface clean and shiny? Although the rust has to be removed from the metal, it is not advisable to make sure that the surface is clean and shiny as, when you try to apply the paint system, the primer will not be able to adhere to the surface as there will be no key for the paint to stick to.

Check it out 1

2 3




Why do you have to ‘wet in’ prior to applying fillers to holes and cracks?

Prepare a report explaining the differences between softwoods and hardwoods and explaining where you may encounter them when working. You should make reference to the properties and possible defects that each type of wood may have. Prepare a method statement, with diagrams, explaining how to use abrasives for timber surfaces. Explain, with diagrams, each stage that may occur during corrosion, focusing on the process of electrolysis. Explain the advantages and disadvantages this process may have. Complete a method statement explaining the best methods for removing rust from metal surfaces. Your statement should explain how to prepare these surfaces for the application of a primer. When spot priming metal surfaces, name two different primers used and which metals they would be applied to. Explain why these primers would be used.


Describe the different types of trowelled and plasterboard finishes you may encounter when working and explain some of the qualities of each. 7 Explain how defective rendering may occur and what can be done to rectify this. 8 Using diagrams and photographs, collect examples of the main paint and paper defects you may encounter while working. Explain how these arise and what can be done to rectify them. 9 Prepare a method statement explaining how to remove paint with heat, including reference to the health and safety practices that must be followed to ensure safe working. 10 Explain the purpose behind cleaning surfaces before work and state the best tools and equipment to use for these. 11 Explain the potential problems that can arise when plaster is affected by heat and moisture.

Unit 2019 Know how to prepare surfaces for decoration 2

Getting ready for assessment The information contained in this unit, as well as continued practical assignments that you will carry out in your college or training centre, will help you in preparing for both your end-of-unit test and the diploma multiple-choice test. It will also aid you in preparing for the work that is required for the synoptic practical assignments. When painting and decorating you will need to be able to prepare a range of surfaces to receive coatings. This will include not only new surfaces made from a range of materials, but also surfaces that have previously been painted or decorated. To carry this out you will need to know the techniques and methods used to prepare these surfaces, as well as repairing and making good any defects or damage to the surface before work.

The knowledge you have gained about the different types of surfaces, and the preparation techniques needed for each, will prepare you for any aspect of the practical test where you will need to prepare or repair or surface. These same skills will be vital throughout your career as a painter and decorator. Before you carry out any work, you should set out a plan of action, which will tell you the order in which you need to do things. It will also record a rough timescale for the work you need to carry out, in order to make sure that you complete everything you need to do safely. You will need to refer back to this plan at each stage to make sure that you are not making any mistakes as you work, or missing out any part of the process that you need to work through. Without checking this you could make some serious mistakes that could have an impact on the final build. Your speed in carrying out any tasks in a practice setting will also help to prepare you for the time set for the test. However, you must never rush the test! Always make sure you are working safely. Make sure throughout the test that you are wearing the appropriate PPE and using tools correctly.

Know how to prepare surfaces for decoration 2

• preparing timbers and timber sheet products ready to receive finishing systems • preparing metal surfaces ready to receive finishing systems • preparing trowelled finishes and plasterboard to receive finishing systems • removing previously applied paint and paper ready to receive finishing systems • rectifying surface conditions • repairing and making good surfaces Most of these learning outcomes revolve around learning about the implications of working with different surfaces, and dealing with the defects that could occur as you work with them. For example, for learning outcome three you will need to select the correct processes for rectifying the defects you have learned about when working with plaster, plasterboards, brickwork and blockwork. You will also need to select the correct preparation processes for these surfaces, using the correct tools, equipment and materials to ensure a high-quality finish. Using all of this you will need to prepare the surface to receive the finish, ensuring that you are working safely and being environmentally aware.

Unit 2019

You will need to be familiar with:

Good luck!


Level 2 NVQ/SVQ Diploma Painting and Decorating 3rd edition


Unit 2019 Know how to prepare surfaces for decoration 2 132

1 Which of the following is not a classification of wood?: a hardwood b softwood c gypsum d timber sheet product

6 Which grade of abrasive paper would you class as coarse? a P20 b P80 c P220 d P320

2 Why is knotting applied to softwood structures? a to prime knots in them b to undercoat knots in them

7 Which primer is used on galvanised metals? a universal primer b mordant solution

c to seal knots in them d none of the above

c metal primer d zinc phosphate primer

3 When using fillers what should be done before use? a area should be dusted b area should be wetted in prior to applying filler c area should have loose materials removed d all of the above

8 Which of these describe dry lining? a plasterboards fixed to stud walling b plasterboards fixed to solid walls c plasterboards not used d none of the above

4 What is the best material to use to fill gaps around the tops of skirting boards and around frames? a caulk b stopper c filler d all of the above

9 After using paint stripper on a surface how do you decontaminate the area? a wipe down with a cloth b dry it off c wash it down d sand it off

5 When washing wall surfaces prior to decoration where is the best position to start? a the top b the bottom c the sides d anywhere on the wall

10 When removing vinyl wallpapers from surfaces it is best to what? a score the paper first b wet the paper first c peel the vinyl first d all of the above