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We had a plumbing issue, and to scope out the problem, the plumber cut a few small holes in the drywall (see attached image). He also scooped out the foam insulation that was behind the drywall. My question is: do we need to replace the insulation that was removed before patching the drywall?

If the answer is "yes" then I would appreciate suggestions on which product to use. There are a few spray foam products on Amazon, but I am worried that they will not cure properly due to lack of airflow in the holes.

Thanks!

enter image description here

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The issue with the holes you have is not re-insulating them, but rather the vapour barrier. I cannot tell from the picture whether there was any there previously, but if it is the case , then just fibreglass or spray foam alone is not enough. You'll also have to restore the vapour barrier.

Usually, when fibreglass or spray foam insulation is used, there would be a layer of 6mil plastic right behind the drywall panel if you live in a predominantly heating climate. If your climate predominantly requires cooling, the barrier would be against the outside sheathing and thus a non-issue in your case.

If there was no vapour barrier, you can just stuff the hole with regular insulation, and cover with the existing cutouts or new pieces of drywall. No new barrier needed.

If a vapour barrier is required, then the simplest patch is to use closed cell expanding foam insulation (e.g. GreatStuff from dupont). Fill the hole with fibreglass or pieces of spray foam insulation until there is at most 3inches of space left.

Then fill the hole with an expanding closed cell foam suitable for the size of the gap, and let it expand, even it expands out of the cutouts. Ensure that enough goes behind the drywall so that it seals with the existing vapour barrier that is behind the drywall. Once cured, after about 15min, cut the excess off with a sharp utility knife, and cover.

Working with expanding foam is messy. Tape and cover off the work area, and wear gloves.

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  • 3
    If you get the foam on your skin, it will wear off after about 3 days. If you get it on your clothes, it will wear off after about 3 years.
    – FreeMan
    Oct 14 at 12:42
  • 1
    @FreeMan and if it gets in your hair, you need a hair cut...
    – P2000
    Oct 14 at 13:48
  • Acetone (and some nail polish removers) will help with cleanup. Oct 16 at 21:58
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    @AloysiusDefenestrate yes, and be very careful; if you get acetone on your fingers, don't touch your glasses, as even minute amounts will dissolve spots of lens coating
    – P2000
    Oct 17 at 7:17

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