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Questions About Drywall And Green Glue on Back of Subfloor

post #1 of 9
Thread Starter 
A few of quick questions for those of you that have used DW and GG on the back of your subfloor.

1) I understand the recommended screw length for 5/8" DW and 3/4" subfloor decking is 1-1/8". This sounds right as it will give 3/8" engagement in the subfloor, but will allow 1/4" extra space to prevent the screw tip from contacting the floor covering above (necessary for carpet, probably for tile, and not a bad idea for hardwoods either).

2) Are standard coarse thread drywall screws recommended?

3) How did you estimate the amount of GG for the pieces that go between the joists? I know it's 2 speedloads for a 4x8 sheet of DW, but once It's cut up, all I know to do would be to lay out my pieces into roughly 4x8 sections and apply the GG.

4) How did you deal with the nails/staples from the flooring above? I've got hardwoods that have lots of staples poking through the subfloor. I initially thought to just hammer them flat, but I'm a little concerned about loosening the staple and flooring above. Should I hammer them flat, or cut them off?


Any other suggestions are appreciated!
post #2 of 9
1. I just grabbed standard 1 1/4" drywall screws. My subfloor was a little thicker then 3/4" I think so didn't worry about this too much. Just make sure not to countersink the screw too deep into the drywall, which is easy to do while trying to balance all that weight with one arm and screw with the other.

2. I used standard coarse.

3. Eyeballed it and double checked along the way with total sq footage a bucket will cover vs sq footage of my ceiling.

4. Dremel with cutting attachment. Went through quite a few of these so recommend the heavy duty ones and some safety goggles. With any stubs leftover, either hammer them or what I did was just put the drywall up there and hit the drywall with a mallet or equivalent to make sure it was flush.
post #3 of 9
Thread Starter 
Using a Dremel tool is a great idea! I always wondered if I'd ever find a need for those little cutoff wheels.
post #4 of 9
The dremel will work, but you will go through a lot of discs if there are a lot of nails from the hardwoods. An angle grinder may be a better choice.
post #5 of 9
Tried cutting them with a multi tool with a metal cutting blade and gave up, just bend them over and hammer flat. Strike at an angle to bend over. See Bethesda Build. If your joists are 16 OC (On Center) use about 1/3 of a speed loader, 12 OC is 1/4. 24 OC is 1/2. This assumes you cut the sheets the short way and I wouldn't recommend the other. Just lay out the number of pieces that require a full load and see how much that is per piece then you will have a feel. I probably tend to use a little more than the calculated amount.
Edited by BIGmouthinDC - 10/9/12 at 4:46am
post #6 of 9
Thread Starter 
I checked the local big box stores as well as a local DW supply house and could not find 1-1/8" coarse thread DW screws. Does anyone know for certain that I can substitute fine thread screws for coarse thread? I'm sure the pullout strength of the fine thread will be lower when going into wood, but I'm not sure if it's enough to worry about.

I would just go with 1-1/4" as suggested by jcorbin above, but in one area the floor above is carpet. So I don't want hundreds of tiny screw points poking though smile.gif Also, I think my decking is 23/32", so slightly less than 3/4".
post #7 of 9
Did you try http://www.fastenal.com ? That's where I bought my screws. They have an online product selector that lets you drill down to get exactly what you want. They have a lot of local stores - 51 in AL. I got the part number, called the local guy, he ordered them for local in store pickup. They about the same price as the DW supply house, much cheaper than Lowes & HD.

When you get around to putting the clips in, the stardrive deck screws from Lowes that Big recommends are nice.
post #8 of 9
here you can get 1000 1 1/8 screws for $20.

http://www.fastenal.com/web/products/detail.ex?sku=32671
post #9 of 9
Thread Starter 
Thanks for tip! I stopped by a Fastenal this morning and ordered some. I didn't even know there was a local store, but I find myself needing specialty fasteners all the time, so these guys will be a great resource!
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