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I want to attach a second layer of drywall to old, partly damaged and crumbling drywall, with construction adhesive. I cannot use screws only because my patch's edges do not fall on studs (the patch will be around 60" x 48" in size).

This new double-layered wall will have to support heavy tiles.

Is gluing an acceptable method to build double-layered drywall wall? Is generic construction adhesive (liquid nails) an acceptable glue for that?

I don't want to replace old drywall because in order to do it properly I'll have to cut a huge hole in a wall that has a vapour barrier and patching it properly afterwards will be very tricky.

More detail: the middle of the area in question is crumbling due to water damage (that has been dealt with, e.g. it should not happen again). However, around it is 10-20" of good drywall, which I hoped I would be able to glue a new patch of drywall to.

My tiles are around 30kg (66lbs) in total weight, and a solid drywall can support such weight in dry area.

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Why would you need to cut a hole in the exterior wall to remove and replace the old drywall? Your tiles will last about 5 minutes if your base is already crumbling and cracked. –  Mel Apr 19 at 2:49
    
@Mel: Sorry, edited my question. I meant exterior-facing wall, where I need to deal with vapour barrier, not disturbing insulation, etc. Adding a second layer of drywall is exactly how I wanted to add a solid base for tiles. Not all of current wall is bad, there is enough ok drywall to glue to. –  haimg Apr 19 at 5:34
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up vote 5 down vote accepted

A good drywall adhesive has much more shear strength than screws - and this is just when your glue is on the framing. So if you are doubling up the drywall gluing makes a ton of sense.

Just recently my drywall guys started using glue and I can say this, I hope I never have to demo these places because the drywall is ATTACHED.

All this being said the glue holds to the back paper of the drywall. What you are saying is that behind the drywall you don't have a solid base... then the glue won't work.

Also I am going to assume that crumbling drywall means moisture. While most glues will be fine with a little moisture, the back paper of your drywall will not.

Then we have to think about heavy tiles. Heavy tiles do not go on drywall. They go on a backer board.

You need to take out crumbling drywall, then install 1/2 inch Hardiboard, then install tiles. There is no reason in the world that you need exterior access to remove interior drywall.

Recap:

  • general purpose Liquid Nails is not a drywall adhesive
  • approved adhesives are just as good or better than screwing - but not applicable to you
  • I wouldn't install drywall when you have an exterior moisture issue
  • drywall can't be used for heavy tiles

  • -
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I just got done gutting a manufactured house with glue and screws. That glue works well and is very strong. I think they used it to place the rock before screwing it off. Definitely made demo a lot harder. –  shirlock homes Apr 19 at 11:20
    
@shirlockhomes - my crew wants to go all glue which is a tiny bit more expensive but the finish is way easier. Some towns let us if they check out the adhesive first. But other towns want to see screws every 16. The adhesives in the past 6-7 years are insane. They have a chemical bond between the paper and wood. I did pull-ups on the last ceiling the next day. Nothing but pluses on glue... except for the demo. We have had to take a couple sheets off here and there and it is at least triple. –  DMoore Apr 19 at 15:12
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