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Spray Foam Problems - shrinkage

Last Post 09 Jan 2010 08:06 PM by gspike. 4 Replies.

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cnygeo

Basic Member

Posts:170

07 Jan 2010 10:33 AM
Hi - I don't know if this is the best forum to post in, but hopefully folks here are as knowledgeable/helpful as they are in the Geo section. I'm very slowly restoring a house in central NY and I had the underside of my roof deck sprayed with ~4 inches of soy-based closed cell foam last October. Due to my slow pace the ceiling is still open and a couple of months ago I noticed that the insulation has pulled away from several of the rafters due to shrinking. It even split one rafter down the middle! It seems like even in the places where there aren't visible splits it is still under tension - I can "pop" it off in some spots with a prybar. I had the walls done previously by the same installer and they are rock solid - no signs of shrinkage/cracking. In fact they added so much rigidity to the structure that was one of my main reasons for doing the roof. The installer seems to be willing to fix it even though it has been more than a year, but I'm not sure what the fix is. I don't just want to spray foam into the visible cracks because I'm concerned that more insulation will pull away over time. Any ideas as to what solution I should persue?
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shortly

New Member

Posts:11

07 Jan 2010 11:58 AM
The only fix is to remove ALL the shrinking foam and spray on new stuff. The most common issues that cause foam to shrink post-application (chemical mix or application temperature) can't be remedied in the existing foam. It'll just continue to shrink. The company I work for shoots literally millions of pounds of urethane annually. I've seen wall sections that were shot at 2 to 3 inches thick shrink to less than half an inch due to an off-ratio mix.

cnygeo

Basic Member

Posts:170

07 Jan 2010 01:28 PM
Thanks for the quick answer. I was afraid of this - I don't know if the installer will be willing to go to that extent to fix it. I'll have to discuss with him... Is there any chance that some of the foam is OK? Can I trust the rafter bays that don't show any signs of trouble yet after a year, or does this tend to happen to a whole batch at once?

shortly

New Member

Posts:11

07 Jan 2010 08:56 PM
You might want to get the manufacturer of the foam chemical involved. They may be willing to test some samples and verify the ratio. There's a slim chance that some is good and some bad. Process control at the chemical manufacturer is normally very good. In almost twenty years of messing with foam I've never had a bad batch of chemical. Every instance of sub-par foam we've encountered we've been able to trace to a temperature or mix issue. The two foam components mix at the gun during application. If the strainers get partially clogged, or any part of the flow control malfunctions you won't get the proper ratio. If the temperature of the chemicals, substrate, or to a lesser extent the air temperature is out of spec it will adversely affect the cured foam. If that happened mid-application, it's possible that the first part of the shoot is OK. See what the chemical company says about testing and keep us posted.

gspike

New Member

Posts:21

09 Jan 2010 08:06 PM
Installer error is also possible especially with half pound foam. It expands a lot and dries fast, if your installer shoots one side of a rafter bay then the other(rather than working from a wet edge), the foam can expand to meet in the middle with a dry or partially dry joint. The joint can then separate with temperature change. If it looks like that is the case spot fixes are adequate but check all the work carefully.