Air seal complex joint
I have a polyiso/wood and polyiso/polyiso joint that I want to air seal. So far I have been using spray foam to accomplish the task. Even with the low expanding, “flexible” window type foam, I’m not very impressed with the integrity of the seal. The foam tears somewhat easily and seems to separate with even modest amounts of force against sealed pieces. I know this problem has been covered extensively. Tapes and gaskets seem like they might be tough to use on this 3D joint complex joint. Caulking seems like it may be more robust but difficult because the gap isn’t uniform. Foam is easy and cheap (I have a “pro” style gun) but integrity seems suspect.
I attached some pictures of the joint. It is where the foam comes down and meets the blocks between the studs. The joint needs to continue out onto the face of the stud and into the next bay. What would you experienced folks use for this seal?
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Replies
Brian,
I suggest that you use one of the European tapes from Small Planet Workshop or 475 Building Materials.
I'd also use tape. It may require several pieces, but good tape will do the job. The European tapes are great, but pricey. The 3M 8067 flashing tape is quite a bit cheaper, but really sticks tenaciously. It is available in various widths. I've used a ton of it air sealing my new house.
For gaps of about 3/8" or wider, and perhaps 1/2" or more deep, I really don't think you can beat spray foam. For smaller, or shallower, gaps, I've used caulk, and a fair amount of acoustical sealant. I guess I'm too cheap to invest in tape, but will admit that where smooth surfaced sheet goods abut one another, I have used it. Specifically, I used foil tape to seal seams of polyisocyanurate insulation panels that butted against one-another.
Looking at your photos, I really don't think you can go wrong with the expanding foam, especially at wood/insulation interfaces.
If you are worried about the integrity of the foam, spritzing the surface of the gap with a little water before foaming may help. I just read Martin's post about this yesterday actually:
https://www.greenbuildingadvisor.com/blogs/dept/musings/justin-fink-s-canned-spray-foam-tip
Two for foam, two for tape; seems like there isn't a strong preference?
I would go with a combination of spray foam and BIg Strech Caulking from Sashco. Spray foam the big joints then go over them with a big bead of Big Stretch. The foam will act as a backer for the Big Stretch. The smaller joints I would go just with the Big Stretch.
Tapes are ok, they have their place but for adhering to semi rough surfaces I would go with the foam and caulk.
Plus spray foam and Big Stretch are quite affordable.