Best sealant for wood framing with SPF?
Hi, I have 2 questions: What should I seal with and how should i seal it given that SPF is already in place. I have 5″ spray polyurethane foam on ceiling and 2″ on the walls. Unfortunately I did not seal anything before they sprayed. I’m now trying to scrap out the foam and seal all the joints and sistered joists. I tried silicon caulking but it didn’t adhere well mostly because I’m not able to completely clean up all the bits of foam. Any advice on a sealant that will stick to both wood and SPF? Also, i’m scraping about a 1/2 inch right now into the bay. (see photo) as the SPF is not an air barrier until 1.5 inch. I don’t know if this necessary or if it’s actually not enough and perhaps I should dig out the whole joint in the bay and seal and then respray. The way i’m thinking is that the crack all the way into the bay is not sealed and will leak air. Thank you. (climate zone 6)
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Replies
Polyurethane sealants stay flexible and stick very well to both wood and SPF. Another benefit is that other sealants will stick to them - nothing sticks to silicone once it's set.
Rather than randomly scraping the SPF out of joints, you should try doing your sealing with the aid of a blower door. With the blower on, a smoke pencil can show you which joints are leaking and which are not, and you can see successful sealing in real-time. You can also find air leaks in unexpected locations that may not be immediately visible.
blower door is a great idea!!
I seem to be lost in a never ending land of different sealants, all claiming to be great. I heard polyurethane sealants melt the existent SPF. Solvent maybe. Anyhow that was my original reason for going with silicon. The silicon is basically just ripping off at some places. I really don't want to make any other mistake. Any advice on what sealant to use? There seems to be so many variants and hybrids.
Flat Roof Trouble,
I recently advised you (in your other Q&A thread on the same topic) to contact your spray foam contractor to insist on a remedy to what seems to have been a defective installation.
My comment was posted here: "Unvented flat roof with SPF underside."
Ok thank you. I guess I'll try regular polyurethane caulk.