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Unread 04-15-2021, 07:24 AM   #1
SWB04
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Join Date: Jan 2015
Location: Coeur d'Alene, Idaho
Posts: 89
Overkill? Durock over wall studs: Add Construction Adhesive?

Question: Should I add Construction Adhesive (probably a poly version) on the wall studs before installing the Durock CBU with CBU screws?

Project: Quartz ledgerstone panels over Durock CBU, for an 18" high kitchen backsplash, (between upper cabinets and a granite countertop).

1) I realize that I probably could have just run thinset over the wallboard (per manufacturer's instructions). However, due to the weight of the stone, I prefer the stability of CBU with CBU screws (versus drywall screws) over a wallboard substrate. Plus, there were issues with the existing wallboard, including insufficient horizontal stud support.

2) Durock installation instructions (http://pdf.lowes.com/howtoguides/081099032585_how.pdf) are clear, i.e. CBU screws to studs, 16" OC maximum, etc..

3) I reinforced the wall with horizontal 2"x3" (i.e. non-structural) studs top and bottom (of the 18" backsplash area) between the 16" OC vertical studs, where I could. Where I could not, i.e. due to plumbing vent or drain pipes, I did the best I could (i.e. putting a stud above the pipe in the middle of the 18" area).

4) It bothers me that there will be places where there is no bottom or top horizontal support for the CBU between the vertical structural studs, to prevent flexing, because I have no way of getting a horizontal stud into those areas. Also, I left a 1 inch "tab" of wallboard top, bottom, and sides where I was able to, to be able to tape & thinset between wallboard and CBU. However, there's about 10' of area where there's a 1.5" gap below the back of the granite countertop, where the wallboard had already separated, (presumably because the drunk on the drywall crew was responsible for that joint). I will extend the CBU below and behind the countertop, and obviously, cannot tape that joint (without pulling out the countertop, cabinets, and destroying a bunch of stuff in the process).

5) Regarding the original question: Should I add a bead of construction adhesive to the studs prior to installing the CBU? The purpose would be to add strength, again, considering the weight of the 1/2" troweled thinset and quarts ledgestone panels that it will support? Or, should that CBU be free floating on the wall, with only the mechanical CBU screw fasteners for support, to prevent normal expansion and contraction from communicating through to the CBU? (Note: I'd like to use the poly version of Construction Adhesive, but may just use Liquid nails from Walmart, so I don't have to make the 1 hour trek into town to a big box store)

Thanks.
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Scott
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