Sealing existing drywall plaster
I have a house in Florida that I have replaced the sheathing, insulated and air sealed the zip sheathing with tape and liquid flash to the concrete block walls below. There are places below a porch roof and garage that were not replaced and less accessible. For the most part, it has existing drywall/plaster. What can I do to seal around the windows/subfloor? For the walls to subfloor, I was thinking spray foam any 1/8 inch – 1/4(largest) inch trim excess and caulk everything. For the windows cut outs, there is often a gap between the plaster and framing. I was thinking spray foam, trim, and use a flashing tape (3M all weather flashing tape) to seal the drywall to the framing. For the outlets, I was planning on fire caulking holes and edges as required.
Any suggestions on other ways to do this? Would this take be acceptable? Or should I use something else? I would love a thinner, less expensive tape. Is taping the drywall to framing worthwhile if already spray foamed?
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Replies
Small 1/8" gaps are usually best sealed with caulk. I like White Lightning for this, or Big Stretch if I think the gap might expand/contract much over time. Canned foam doesn't work well with gaps under about 1/4" or so -- it tends to just stay outside the gap and get chipped off.
I have sometimes used the plastic fine tip for my foam gun (I use one of the metal guns for Great Stuff, and rarely use the cans with the integral plastic straw anymore), which lets me inject canned foam into smaller gaps down to around 1/8" or so -- as long as I can get the plastic tip to stick into the gap. I like to inject canned foam into gaps that I think have voids behind them, since the canned foam will expand to somewhat fill voids.
Basically use canned foam for larger gaps where the foam can fit INSIDE the gap, sealing to the interior of the gap. Use caulk to seal smaller gaps where the caulk can seal to the OUTSIDE EDGES of the gap.
I generally avoid the use of tapes inside on drywall. I like tapes for sealing up exterior rigid foam, things like that, and sometimes also for gaps between sheets of sheathing (plywood, OSB). Tape works well where you can seal to the face of a wide surface to cover an irregularly shaped small gap, or to wrap around an outside corner.
Bill
Thanks for your inputs. I don't know that I described the window opening to drywall condition clearly. I have raw cut edges of drywall that have been cut flush with the framing. All returns were removed to fix some window problems. I'm not sure how to seal that drywall to the framing without tape since most of the gaps are less than 1/16th inch. That's where I was thinking tape. I also stumbled upon a solution of a liquid applied flashing. These all seem strange inside though.
This will ends up getting a wood trim covering any tape if tape was used.
I think it would be tricky to get tape to stick to a cut drywall edge. You'd probably end up with the tape coming off covered with drywall dust and not doing much else. I think your best bet here would be try to seal between the drywall, framing, and trim boards used around the window. That will give you a sort of T-shaped area to apply sealant too. I'd use caulk here, I don't think canned foam will work well unless you have more of a gap in that area.
Bill