Hi, I have an uninsulated poured concrete foundation. I plan to adhere two layers of 2” foam board, staggering the seams, then build a 2×3 wall and hang sheet rock. Thoughts? How do I adhere the foam board to the concrete? PL 300 or spray foam or something else? The forms used to pour the foundation left uneven ridges so I think I will have to cut the foam to apply to either side of these ridges and use spray foam to fill the gap. Otherwise the foam board will not lay close to flat.
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Rather than trim around the uneven joints, you can get one more sheet of foam, in a thickness that is more than the ridge, and cut strips to use as spacers. (half inch should work. you can measure)
PL 300 or similar should work fine. just need a blob every couple feet. The foam just needs to stay in place well enough to keep your air seal surfaces in place. (since you plan a stud wall inside)
I like a pro foam gun and foam adhesive cans. This will let you run a thin bead along the edges between panels. Enerfoam from dupont is designed as a sealant and adhesive.
You will also want to insulate and seal up the floor rim joist and associated interfaces above the poured wall.
The consensus is definitely pl300. and/or mechanical fastening with screws/nails with a plastic washer to distribute the weight across the front of the foam board. I would not have the foam board touch all the way to the ground. I'd use an 1/8" scrap piece of wood under your rigid foam panels and then once all done, use spray foam to fill in that space and then once dried trim the spray foam flat before your 2x4 wall Use pressure treated bottom plate and sill gasket under it. Make sure you not only use spray foam or pl300 between two sheets left to right but also i'd tape the seams either using duct mastic or caulking or seam tape like tyvek or other.
Thank you for the help, some great suggestions, I appreciate it!