The Detection of Stud Line Cracking in
Metal Stud Walls
Steven P. Crain, Dalwinder Gill, Medhat Hanna,
Donald LeBlanc
Collaboration for Cold Weather Spray-Applied Polyurethane Foam (SPF) Insulation
Dow Building Solutions (DBS)
The DBS business offers a broad line of product solutions while addressing the issues most important to builders and home buyers including:
¾ energy efficiency, moisture resistance and durability
Dow Polyurethanes
Dow's polyurethane products and fully-formulated polyurethane systems are used for a broad range of applications including
¾ construction, infrastructure repair, wind energy solutions, automotive, appliance, furniture, bedding and shoe soles to decorative molding, athletic equipment and more
Center for Surface Transportation Technology, National Research Council of Canada
CSTT is improving the reliability, safety and competitiveness of rail and road transportation equipment and systems by providing clients with
¾ climatic simulation, vehicular engineering research and development, computer modeling and analysis, field testing and vehicle performance testing
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Why Choose Spray Foam (SPF) Insulation
Fast Application
¾ No measuring and cutting required for odd shapes and narrow spaces ¾ Saves labor during installation
¾ Foam forms and stays exactly where you put it
Safe for the Environment
¾ Contains no formaldehyde
¾ Contains no ozone depleting chemicals ¾ Does not release toxic gasses
¾ Requires less energy to produce than the leading cavity insulation
Energy Efficiency
¾ Highest R-value/inch cavity insulation
¾ Air barrier functionality to reduce air infiltration
¾ Can qualify for “green building” certification points (i.e. LEED, NAHB) ¾ Reduce heating and cooling fuel needs, and thus reduce global warming
Installation Method for Medium Density SPF to Wall Cavities
Starting materials
Delivery method
Wall insulation example Picture frame technique
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Mock Wall Construction
4x8 ft wall
¾ Three unevenly sized cavities – 8, 16 and 24 inch OC ¾ Footer sat on concrete floor
¾ Type T thermocouple at center of 24 inch OC cavity, 1 inch into cavity
Commercial Wall
¾ 2 x 3-5/8 inch, 16 gauge steel studs ¾ THERMAX™ brand insulation sheathing
¾ Extra metal stud at header to simulate construction practices
¾ Foam Deflection Force Gauge (FDFG) at position 12 for Commercial Walls only
Residential Wall
¾ 1.5 x 3.5 (2x4) inch pine studs ¾ OSB sheathing or
¾ STYROFOAM™ residential sheathing 16"16"
48" 48" 96" 96" 24 24 " " 8" 8" 16"16" 48" 48" 96" 96" 24 24 " " 8" 8" 1 2 3 4 5 6 7 8 9 10 11 12
Problem Statements
Stud line cracking occurs if spray-apply
polyurethane system at too low of
substrate temperature
¾ Poorer moisture/vapor barrier ¾ Poorer air and particulate barrier
Difficult to observe stud line cracking for typical
commercial building walls using c-channel studs
Steel foam interface Flat side of stud
Steel foam interface
Cavity side of stud Steel foam interfaceCut-away view Example of improperly applied foam – too cold
SPF Wood header and stud
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Potential Analysis Techniques (stud line cracking –
point of the
story
)
Hypothesis
Stud line cracking can be avoided at the lowest desired substrate temperature through formulation changes
(not the point of the story)
Define success – then find the appropriate measuring tool Wood stud walls as model for metal studs
¾ Compare metal stud foam delamination with wood stud foam delamination
ª Adhesive failure – wood vs steel
ª Time and place of cracking – wood vs steel
Delamination sounds
Deconstruct spray-applied walls and look for cracks
Install a pressure sensor to evaluate foam rise and shrink forces of the foam – a Foam Deflection Force Gauge (FDFG)
Define Success
Residential – visual crack <1/16 inch
Commercial – no delamination from FDFG
Residential walls – post-deconstruction y = 8.5532x + 9.617 R2 = 0.678 0 10 20 30 40 50 60 70 80 0 1 2 3 4 5 6 7 8
Aged Crack Width (mm)
A g ed C rac k D e p th ( m m ) 1.59 mm (1/16") width max
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Stud Line Failures – Compare Wood vs Metal Stud
Residential wall (wood) – where does failure
occur?
¾ When failure occurs, cracking generally starts at position 2
¾ Generally if cracking has occurred at 10, then there are cracks at positions 1-9
¾ Most cracking for formulations evaluated ended in positions 2 or 3 – see chart below
16" 16" 48" 48" 96" 96" 24 24 " " 8" 8" 16"16" 48" 48" 96" 96" 24 24 " " 8" 8" 1 2 3 4 5 6 7 8 9 10 11 12 position
Stud Line Failures – Compare Wood vs Metal Stud?
Commercial Wall (metal) – where does failure
occur?
¾ Time (min) to failure similar between commercial (FDFG) and residential walls (visual) – generally within 35 minutes
¾ Positions 1, 2, 4, 6-12 were visually inaccessible
16" 16" 48" 48" 96" 96" 24 24 " " 8" 8" 16"16" 48" 48" 96" 96" 24 24 " " 8" 8" 1 2 3 4 5 6 7 8 9 10 11 12 Commercial
(FDFG data) Residential(visual data) Conclusion – cannot confirm if failure point is the same as residential
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Failure Comparison – Post Deconstruction Analysis
Delamination Failure - Metal
¾
Metal studs delamination primarily cohesively
¾
Except when metal stud had ice – adhesive failure
Delamination Failure – Wood
¾
Primarily adhesive failure
¾
Exception was cohesive failure where mechanical interlocks possible
Failure Analysis – Delamination Sounds
Previous work with spray-applied walls
¾
Small sounds = narrow cracks
¾
Loud sounds = large cracks (>1/16 inch)
¾
Qualitative
¾
Dissimilar construction components rub when heating and cooling
¾
And which wall made the sound?
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Failure Comparison – Post Deconstruction Analysis
Observation of wood stud walls after 1 month associated with shipping
¾ Cracks were not visible in 11 out of 23 original cracked walls ¾ Cracks that healed had started at <1/16 inch
¾ Suspect foam expansion when removed from Climatic Chamber
Conclusion – deconstruction analysis would potentially give false positives –
incorrect crack width and number of cracks
Initial thickness (mm)
Initial foam thickness of
those that subsequently
healed
Initial foam thickness of
those that did not heal
Foam Deflection Force Gauge Construction
Omega’s LCFA-5
• strain gauge transducer
• Four-arm Wheatstone Bridge
(strain changes resistance)
• 5 LB + 1% full scale • aluminum construction 1 2 3 4
1. Bracket with supports
2. Cylinder attached to LCFA-5 and sitting flush with hole
3. C-channel header
4. THERMAX™ brand isocyanurate insulation sheathing
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Foam Deflection Force Gauge Data Description
Push Force
Push Force
Push to Pull Time
Push to Pull Time
Pull Force
Pull Force
Foam Deflection Force Gauge Data Description
Picture frame
Foam rise complete (<10 sec) Bulk Foam Addition
started
Max Exotherm
Temperature at this point
30F
110F
95F
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Foam Deflection Force Gauge – Source of Errors
Lateral Forces – foaming pressure pushes cylinder sideways against hole edge, as pull pressure becomes strong enough, the foam drags the cylinder down across the edge Under coverage of foam – more foam added on one wall versus the second leading to
different absolute pressure values although the same pass/fail
Lateral forces
Foam Deflection Force Gauge – Example of Chemical
Temperature Affect on Max Foam Temperature and Pressure
Profile
DOW CHEMICAL CLIMATE ROOM TESTSMay 25, 2009, Runs 14, 15 & 16 DOW 381, OAT = 30°F 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 14:40 14:45 14:50 14:55 15:00 15:05 15:10 15:15 15:20 15:25 15:30 Time of Day Te mperature (F) TC_1 TC_2 TC_3 TC_4 TC_5 TC_6 Gun_T_1 Gun_T_2 TC_1 - Run 14A - TWS TC_2 - Run 14B - TWS TC_3 - Run 15A - OSB TC_4 - Run 15B - OSB TC_5 - Run 16A - XPS TC_6 - Run 16B - XPS
mock wall - THERMAX™
Sheathing Attached to Steel Studs
mock wall - STYROFOAM™ XPS Attached to Wood Studs
mock wall - OSB Attached to Wood Studs
Chemical Temperatures Prior to Spray-gun
Pressure Profile from the FDFG for Mock Walls THERMAX(tm) Over Steel Stud Walls at 30F Substrate
Temperature -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 3000 4000 5000 6000 7000 8000 14A-lbs/inch 14B-lbs/inch
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Conclusion
The Force Deflection Force Gauge (FDFG) was able to detect foam compressive
and tensile forces
¾ Differing environmental conditions ¾ System temperature differences ¾ Formulation differences
The foam continues to build internal pressure after rise as the exotherm
temperature increases
As the foam cools, tensile forces can lead to delamination from the FDFG –
considered a failure of the foam system
The FDFG was able to detect failure through delamination indicating crack >1/16 of
an inch
Wood and metal stud mock walls did not always correlate with stud line cracking –
there would have been up to 25% formulation false positives without the FDFG
The system chosen for commercialization performs well in the field to the design
minimum temperature
On site since 1965 – 45 acres
Cost recoverable technology centre of
NRC since 1995
Consulting Engineering organization
¾ Civilian, OGD and military clients
¾ Road
¾ Rail ¾ Climatic
120 specialized staff including
ª Engineersª Project managers ª technologists
CSTT – Centre for Surface Transportation Technology
National Research Council Canada Centre for Surface Transportation Technology
2320 Lester Rd Ottawa, ON K1V 1S2
Don LeBlanc P.Eng
Email: [email protected]
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Dow Building Solutions
Websites
STYROFOAM™ Spray Polyurethane Foam Insulation: www.sprayfoamatdow.com
THERMAX™ Wall System: www.thermaxwallsystem.com
Technical Support
Customers can contact CIG with questions: 1-866-583-BLUE (2583)
Other Websites
Center for the Polyurethanes Industry: www.polyurethane.org International Residential Code (IRC): www.iccsafe.org
International Code Council (ICC): www.iccsafe.org/e/category.html
NAHB Green Building Program: www.nahbgreen.org
Spray Polyurethane Foam Alliance: www.sprayfoam.org LEED for Homes:
http://www.usgbc.org/displaypage.aspx?cmspageid=147
Federal Trade Commission, "Labeling and Advertising of Home Insulation": http://www.ftc.gov/bcp/rulemaking/rvalue/16cfr460.shtm
Code College Online Video Training:
http://www.codecollegenetwork.com/video_center/
