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Evaluation and Repair p of Thin Brick Veneer Facades Carolyn L. Searls Janelle L. Leafblad 22 February 2010
Outline • • • •
Definition System Examples and Modes of Failure Review of Standards and Codes Recommendations for Repairs to Existing Construction • Recommendations for New Construction Design
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What is “Thin Brick Veneer?” • 3/8 to 3/4 in. thick brick • Three basic installation systems: – Embedded in precast concrete panels – Adhered to sheet metal or insulation panels – Site-adhered to exterior cement plaster or concrete walls
San Francisco Museum of Modern Art 151 Third Street, San Francisco, CA Brick precast into panels
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AT&T Park (Home of the San Francisco Giants) 24 Willie Mays Plaza, San Francisco, CA Brick precast into panels
Golden Gateway Commons 560, 650 Davis St. and 75 Broadway, San Francisco, CA Site-adhered to cement plaster and precast concrete walls
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Sheraton Norwood 1125 Boston Providence Turnpike, Norwood, MA Panelized wall system – cement board on steel studs
Liggins Tower 5150 E 34th Avenue, Denver, CO Brick precast into panels
Outline • • • •
Definition System Examples and Modes of Failure Review of Standards and Codes Recommendations for Repairs to Existing Construction • Recommendations for New Construction Design
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Thin Brick in Precast Concrete Panels • Manufacturing process – negative cast most common • Joints filled with “face face mix” mix from back or pointed from front after panel is manufactured
Thin Brick in Precast Concrete Panels • Negative cast panels • Guidelines: G id li PCI D Design i H Handbook db k • Brick selection: – ASTM C 1088 Type TBX –tolerance – ASTM C 216 water absorption by boiling – 6% to 9% – Soak brick w/ IRA above 30 g/30 sq in/min. before placing concrete – Scored back for better bond
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Thin Brick in Precast Concrete Panels • Bowing of Panels – Shrinkage of concrete – Expansion of clay brick – Control by design of panel size, panel thickness, reinforcement and concrete mix design
• 30 year old building in Denver – Some bowed panels – No other signs of distress
Panelized Wall Systems: Cement Board and Steel Studs • Steel-stud framed panelized system • Manufactured and marketed on east coast Thin brick (adhered with mortar) Fluid applied waterproofing Cement board Insulation Self adhering sheet membrane DensGlass Steel studs
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Panelized Wall Systems: Cement Board and Steel Studs • Concerns: –N No ttrackk record d – Barrier wall system – Air barrier compliance – Freeze thaw durability – Bonding of thin brick
“True weather barrier systems, eliminating the need for elaborate and expensive weep systems” --Manufacturer’s literature
Panelized Wall Systems: Brick Adhered to Metal Panels • Thin brick glued to aluminum or galvanized steel panels • Over rigid insulation • Nailed to plywood sheathing • Concerns: – Brick adhesion – Entire system separating from building
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Panelized Wall Systems: Brick Adhered to Polystyrene • Thin brick glued with ribbons of adhesive to insulation • Insulation adhered and attached with metal clips to CMU wall • Failure under low wind load – Brick unadhered or poorly adhered – Metal clips remain nailed to CMU
Brick Individually Installed On Site • Thin brick veneer over exterior cement plaster, reinforced concrete or precast concrete – – – –
Metal studs Exterior sheathing Water-resistive barrier 2 – 3 coats exterior cement plaster • Scratch coat, brown or “bond” coat, optional p skim coat
– Thin brick back-buttered with mortar using a notched trowel – Joints either pointed with mortar or left open for raked appearance
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Site-Adhered Adhesion Failures
Site-Adhered Adhesion Failures • Detection methods – Tapping • Correlation between “sounding” and shear bond strength – Prying
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Site-Adhered Adhesion Failures • Causes – Poor initial bonding – Improper mix proportions of bonding mortar – Incomplete hydration – Improper wetting of the substrate – Open joints that allow water to leach out cement paste
Site-Adhered Adhesion/Construction Failures • Unzipping parge coat • Causes – Inadequate surface preparation – Bonding agent failure
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Site-Adhered Construction/Waterproofing Failures
• Unsealed joints
Site-Adhered Construction/Waterproofing Failures
• Inappropriate termination of the veneer system
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Site-Adhered Construction/Waterproofing Failures
• Rusting cement plaster accessories
Site-Adhered Construction/Waterproofing Failures
• Rebar too close to substrate surface
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Outline • • • •
Definition System Examples and Modes of Failure Review of Standards and Codes Recommendations for Repairs to Existing Construction • Recommendations for New Construction Design
Brick Individually Installed On Site: Standards and Codes • TCA Requirements - TCA Methods W231 and W241 – Typical yp ca system, sys e , additional add o a requirements: equ e e s • Movement joints at 8’ – 12’ o.c. • Adhere with latex portland cement mortar or dry-set mortar (portland cement mortar w/o latex)
• BIA Technical Notes 28C: Systems Available – – – –
Thin-set over wall board (interior only) Thick-set method (similar to TCA) Prefabricated panels Modular panels
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Building Code Requirements Code
Shear Strength
Testing
1997 UBC
50 psi
1997 Mass. Bldg Code Bldg.
50 psi
After 28 days
2006 IBC
See Article 6.1 and 6.3 of TMS 402/ACI 530/ASCE 5
Special inspections may be required by state or city code
CA Bldg. Code: 2 or more tests required 1 test per 5,000 sq ft floor area Test to min. 100 psi
TMS/ACI/ASCE • 2006 IBC refers to TMS 402/ACI 530/ASCE 5 • TMS 402/ACI 530/ASCE 5 contains limitations on: – Unit sizes – Wall area – Backing • Permitted: masonry, concrete, metal lath and portland cement plaster applied to masonry, concrete, steel framing, or wood framing – Adhesion • 50 psi shear strength (using ASTM C482), or • Compliance p with Article 3.3 of ACI 530.1/ASCE 6/TMS 602 ((a description of how to place adhered veneer)
• ASTM C482 is the standard laboratory test method for shear bond strength between ceramic tile and portland cement mortar
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Outline • • • •
Definition System Examples and Modes of Failure Review of Standards and Codes Recommendations for Repairs to Existing Construction • Recommendations for New Construction Design
Repairs to Existing Construction • Repairs – Brick matching – Salvaging brick – Re R adhere dh b brick i k • In large areas of replacement, apply thin-set to substrate and back-butter veneer
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Repairs to Existing Construction • Repairs – Brick matching – Salvaging brick Thin Brick – Re R adhere dh b brick i k • In large areas of replacement, apply Bonding thin-set to substrate Mortar and back-butter veneer Mortar in Key – Point joints • Routing a “key”
ROUTED
UN-ROUTED
Repairs to Existing Construction • Repairs – Brick matching – Salvaging brick – Re R adhere dh b brick i k • In large areas of replacement, apply thin-set to substrate and back-butter veneer – Point joints • Routing a “key” • Grout pump p p • Hand-packing • Concave join profile
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Outline • • • •
Definition System Examples and Modes of Failure Review of Standards and Codes Recommendations for Repairs to Existing Construction • Recommendations for New Construction Design
New Construction • • •
Waterproof the building envelope Accommodate structural movement Limit substrate deflection (steel stud wall design) – 16” oc max spacing – L/600 deflection limit
•
Selection of materials – Substrate: concrete or cement plaster – Bonding mortar: polymer modified – Water-resistive barrier: 2 layers of 60 min. bldg paper – Point joints, do not leave open
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Testing During Construction • Shear strength of adhesive bond only • Shear strength of joint mortar only • Shear strength of both • Shear test corner units • Pull-off test of newly installed brick • Efflorescence – Potential for efflorescence – Cleaning off efflorescence
Thin Brick Veneer Conclusions • Popular and economical wall cladding system B t... But – Failures • Adhesion of thin brick • Waterproofing and durability of cladding system
So, if repairs are feasible . . .
– Repairs • Correct waterproofing deficiencies in wall systems • Re-adhere brick • Point joints
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Thin Brick Veneer Conclusions • New Design – – – –
Low initial cost vs. expected life and required maintenance Barrier wall vs vs. drainage wall Best track record: precast concrete panels Other systems with adhered thin brick
• Design Considerations – Design to consider structural movement, waterproofing, air barriers – Adhesion of brick – Fill joints – do not leave open – Quality control and testing
• Be careful, so you don’t have…
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Carolyn L. Searls, P.E. Senior Principal Simpson Gumpertz & Heger The Landmark @ One Market St., Suite 600 San Francisco, CA 94105 (415) 495-3700 www.sgh.com
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