Is there a compatible spray foam to be used with Type IX- EPS foam?
Hello,
We are building a new home. Beneath the basement slab we are planning to install two layers of EPS Type IX foam board (2.0 density) 1.5 inches thick. We will stagger the joints. During shipping some of the boards have minimal damage along the edges. Is there a compatible spray foam that I can use to fill in any voids. I have been told by the manufacturer of the insulation to avoid any spray foam that has a petroleum base. However, when pressed they did not offer advice as to a specific spray foam product. Secondly, we plan to tape the seems of the insulation boards. Again, is there a recommended tape to use for this application.
Thanks,
William
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Replies
The reason why you're supposed to use spray foam here is because it's an insulator and air barrier all in one. This suggests that you can use a non-air-barrier insulation as long as you provide your own air barrier to prevent air from blowing through it. So as a slightly slapdash alternative, you could probably thickly stuff loose mineral wool or fiberglass (whatever's handy), into those cavities and tape over it with whatever you were planning to use to tape the joints. The tape acts as an air barrier and keep its performance intact.
William,
As far as I know, you can use any common canned spray foam. None of these common spray foams have components that will hurt your EPS.
It never hurts to tape the joints of rigid foam insulation, but high-quality tape is expensive, and you may want to skip the tape in this location. Your concrete slab is an excellent air barrier; the EPS under your slab is there to provide R-value. The EPS is not an air barrier, so you don't really have to tape the joints.
If you want to tape the EPS, you could choose Siga Sicrall, Siga Wigluv, or 3M All Weather Flashing Tape. I base that advice on the results of tests performed on XPS. For more information on my tape test, see Return to the Backyard Tape Test.