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Evaluation and Repair of Thin pBrick Veneer Facades

Carolyn L. SearlsJanelle 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:• 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 Art151 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 Commons560, 650 Davis St. and 75 Broadway, San Francisco, CA

Site-adhered to cement plaster and precast concrete walls

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Sheraton Norwood1125 Boston Providence Turnpike, Norwood, MA

Panelized wall system – cement board on steel studs

Liggins Tower5150 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 mix” from back or pointed from• Joints filled with face mix from back or pointed from front after panel is manufactured

Thin Brick in PrecastConcrete Panels

• Negative cast panels

G id li PCI D i H db k• Guidelines: PCI Design Handbook

• 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 PanelsShrinkage of concrete– 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 DenverDenver– 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• Manufactured and marketed on east coastThin 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 t k d– No track record

– Barrier wall system

– Air barrier compliance

– Freeze thaw durabilitydurability

– 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 galvanizedaluminum or galvanized steel panels

• Over rigid insulation

• Nailed to plywood sheathing

• Concerns: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 toribbons 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 concretereinforced concrete or precast concrete– Metal studs

– Exterior sheathing

– Water-resistive barrier

– 2 – 3 coats exterior cement plaster• Scratch coat, brown or “bond” coat, optional skim coatp

– 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 toRebar 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 system, additional requirements:yp ca sys e , add o a 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– Prefabricated panels– Modular panels

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Building Code RequirementsCode Shear Strength Testing

1997 UBC 50 psi CA Bldg. Code:

2 or more tests required

1 test per 5,000 sq ft floor area

Test to min. 100 psi

1997 Mass.

Bldg Code

50 psi After 28 days

Bldg. Code

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

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 with Article 3.3 of ACI 530.1/ASCE 6/TMS 602 (a p (

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

R dh b i k– Re adhere brick

• 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

R dh b i k Thin Brick– Re adhere brick

• In large areas of replacement, apply thin-set to substrate and back-butter veneer

– Point joints

• Routing a “key”

Thin Brick

Bonding Mortar

Mortar in Key

ROUTED UN-ROUTED

Repairs to Existing Construction• Repairs

– Brick matching

– Salvaging brick

R dh b i k– Re adhere brick

• In large areas of replacement, apply thin-set to substrate and back-butter veneer

– Point joints

• Routing a “key”

• Grout pumpp 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)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 onlymortar 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 tBut . . .

– 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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• New Design– Low initial cost vs. expected life and required maintenance– Barrier wall vs drainage wall

Thin Brick Veneer Conclusions

Barrier wall 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 & HegerThe Landmark @ One Market St., Suite 600

San Francisco, CA 94105

(415) 495-3700www.sgh.com