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roofing foam shrinkage Post New Topic | Post Reply
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Thomas Tisthammer
Posted: Nov 14, 2012 08:19 AM
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roofing foam shrinkage
Judging from the number of posts regarding SPF shrinkage related to low density/wall foams I'm wondering if other are noticing shrinkage with the roofing materials. Several of the roofing guys I've contacted have seen it, especially in materials installed during the last 2-3 years. It doesn't show up until the material has been in place for some time (2-3 years) and then it first appears at dissimilar materials transitions. It pulls away from the foamstops and separates at the edge of patches. This is not an installation technique issue since the materials are the only variable in these situations. Materials exhibiting this phenomenon are matched to the existing SPF (density & compressive)and are supplied by reputable manufacturers. Having seen this in the past when large amounts of fire retardants were first introduced into the freon formulations I suspect that dimensional stability is a root cause. The ASTM 2126 test was changed about the time the 245fa blowing agents were introduced and dimensional stability values sharply declined as a result of modified test. Since blistering, splitting, cracking, etc. are the result of SPF movement, I suspect that the new 2126 values no longer accurately reflect the in-field stability performance we observed with the 141b foams. In summary, we have installed SPF in roofing applications for many years without observing this condition and recently it has caused us to make leak repairs. Cell structure is fine and consistent; compressives are within spec and consistent;. application is well within manufacturer's requirements and the installed material has excellent an profile. Anyone have any similar experiences?
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mason
Posted: Nov 23, 2012 09:11 AM
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Bad pattern, I conduct quite a few roofing inspections each year and frequently consult on other roofing projects with a wide range of suppliers and contractors. I am not aware of a lot of shrinking foam issues with roofing foam made with HFC 245fa blends. The older foams made with HCFC 141b did have dimensional stability problems (creep) the first few years but then suppliers were able to modify the formulas to provide a more stable foam. As for the dimensional stability test, I am chair of the ASTM Committee that maintains ASTM C 1029, the specification for closed cell sprayfoam. The original dimensionally stability test specified in ASTM C 1029 for closed cell roofing foams was flawed. It did not have a reliable degree of reproducibility from one sample to another (from the same batch of foam sprayed on the same day). Consequently the values reported were pretty meaningless. A better predicator of dimensional stability is compressive strength and density. Also, the numbers derived from the old sample preparation were not representative of a foam that was being successfully installed in the field. We adopted a new sample preparation, installing the foam to a substrate and measuring the degree of volume change in a linear direction. This is more representative of what happens in the field and the values are also more representative of the foams that have been installed in roofing applications for decades. I expect a roofing foam to have an in place density a little bit higher than the density on the data sheets. For example if the core density is 2.8 pcf, the sprayed in place density would be around 3.2 to 3.4 typically, The more lifts the greater the density as well as each high density skin that forms on the substrate and the surface of the foam increases the overall density. I would be happy to investigate your situation. Give me a call at 571-239-5221 or email masonknowles@aol.com |
