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Discussion Starter · #1 ·
Hi All - Several searches have not revealed the answers I seek, so here goes:


1) Any special type of drywall? I know I need to use 5/8 followed by 1/2, but do I need the type X or anything special?


2) Based on info here, it appears that I should tape and mud both the first and second layer. Anyone care to offer another opinion?


3) Acoustical caulk??? Where does one use acoustical caulk? Around electrical boxes and other penetrations in the acoustical envelope? If I mud and tape the corners, do I need caulk there as well?


4) Layout: In the theater space, I planned to orient the first layer parallel to the joists and the second perpendicular. Care to correct me on this one?


5) To laminate or not? Should I laminate the second layer to the first, or just use longer screws and screw the second layer to the joists? If I laminate, what adhesive should I use?


Thanks for any answers or opinions you have!

Jeff
 

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1) Type X, ake Fire Check is denser / heavier. I'd use that instead. I tend to use 5/8" layer followed by another 5/8" since the local stores only carry type X in 5/8". If you can get 1/2" in the same, I'd use that instead for the outer layer.


2) Yes, tape and mud, but obiously you can go easy on the sanding of the first layer. Same goes for the second layer if yo are covering with additional materials. If you have the right tools and are careful with the mud, you shouldn't have to sand much at all.


3) You caulk anywhere there is a penetration or seam that isn't covered by mud. In fact, I caulk the sill plate on both sides before and after the drywall goes up, so I run 4 beads total for the floor. Overkill probably, but I usually do not have a raised floor, so this untaped seam is quite important.


4) I have no preference, as long as the seams are staggered. Whether the sheets are oriented the same way doesn't matter, as long as you offset the starting corner, all will be offset by the same amount, and you will never have a seam directly over another seam. Crossing seams are ok. Parallel seams are ok. Parallel seams on top of each other is bad. For me, I've just found it easier to start the first sheet in a particular corner whole, and then I take a quarter sheet (usually a cutoff scrap from the first layer) and start in the same corner for the second layer. This guarantees no overlaps.


5) Even if you drive into the studs, you should still laminate with construction adhesive. However, since you are already laminating, you do not need to screw into the studs, but you do have to screw into the other layer of drywall for safety. The papers you are bonding are not the strongest stuff. If you laminate, be sure you use LOTS of 1"coarse thread drywall screws so at least the outer layer is physically bonded into the inner 5/8" layer. In my case I use 5/8" over 5/8", so 1" screws are perfect, they will not drive into the studs even when coutersunk aggressively. However, I don't see a major problem driving right into the studs. They key is to bond the panels with lots of adhesive so they don't resonate individually. Of course, like the ceiling, stagger your seams.


Hope that helps.


Rhino
 

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Rhino, I just bought some Bulldog accoustik-seal from HD. It's black in color. Are those the correct type of accoustic caulking I should use? I am thinking to have a bead under the bottom sill plate.

Thanks

Ken
 

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Discussion Starter · #4 ·
Quote:
Originally posted by RhinoDude
If you laminate, be sure you use LOTS of 1"coarse thread drywall screws so at least the outer layer is physically bonded into the inner 5/8" layer. In my case I use 5/8" over 5/8", so 1" screws are perfect, they will not drive into the studs even when countersunk aggressively.
I'm just about ready to put up the second layer of drywall and have preformed a few "tests". I tried countersinking different types of drywall screws in a couple of pieces of scrap. Course or fine, long or short, none would countersink without hitting wood. Is there some trick to getting the screws to countersink without wood behind them?


Thanks

JE
 

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It should be noted that you don't have to use the type X unless it's specifically required by local code. The only thing I used it for was along the ceiling behind the perimeter walls. Basically this was to isolate the void space behind the walls from the joist cavities above the ceiling. This was a measure to prevent fire spread.
 

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Discussion Starter · #7 ·
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Originally posted by ChadA
Just curious, what is the benefit of mudding and taping the first layer? It seems like a lot of extra work.
Mudding and taping the first layer is intended to seal up the seams. The goal is to keep everything as air tight as possible, and mud / taping the first layer helps accomplish this.


Now, who knows the trick to getting the screws to countersink when they don't hit wood???
 

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I also had problems with the laminating screws. Here's what I found. If you are using a drywall screw gun....don't. Use a regular heavy duty variable speed drill with a regular Phillip's bit. You have to exert a LOT of pressure (I think about 100 lbs of lift) and turn the drill bit on the slow side. You'll need to stand right under the drill (for ceilings) to get the pressure I'm suggesting.


Another thought ....from what I've read, the laminating screws are considered temporary. Assuming you've glued the two sheets together they can come out. I'm only planning to take out those I can't get seated.


I was able to get about 80% seated with the method I described.
 

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(I'm not a contractor, nor a building inspector)

I've also read that you can glue two sheets together with Liquid Nails For Subfloors. But only the walls and floor are glueable. Don't dare try glue only on the ceiling.:eek: The ceiling needs screws.

You put up one layer of drywall with screws, then cover it with Liquid Nails for Subfloors, then put up the second layer of drywall with a few screws. Wait a couple of days then take the screws out of the second layer.
 

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I did not (and would not) mud and tape the first layer. That's a horrible waste of time and effort in my opinion. Just use some caulk down the middle of the seam, and make sure that layer number two is staggered. Corners should be lapped (I think I got that right, as I always forget which is which).


Anyway, I think the work involved in mudding seams will gain you very little over simple caulking.
 

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The first layer should be sealed with acoustic caulk (no tape and mud) - quick, effective and easy.


The second layer gets tape and mud.


Why would you not screw into the studs / joists for the second layer?
 

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I used the self adhesive paper perforated tape and a single heavy layer of mud to fill in the recess of the tapered seams. That gives you a nice flat surface for the second layer of drywall. No need to sand just put on the layer with a 12 inch blade. Goes real fast.


Two-rocks : In my case the first layer was on RC2 channel and you don't want to mechanically connect the drywall to the ceiling joists because it defeats the purpose of the RC channel. Also since the second layer is staggered there is no real reason to line the seams up with anything you just want to attach it to the first.
 

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BIGmouthinDC wrote
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At HD they sell drywall adhesive in the large tubes. I think it's OSG brand. I used about one large tube per sheet. At HD you can buy it in cases of 12 a lot cheaper than the Liquid nails stuff.>
Yes but rumor has it that the more expensive 'liquid nails for subfloors' has a different effect because it never drys. The idea is that it creates a stretchy layer between the two layers of gypsum that resists stretching elastically when the gypsum bends into a curve. Glue doesn't have this stretchy effect. I think it's called Constrained Layer Damping or something like that. The effect is greater at low frequencies, which traditionally are a problem for sound isolating walls.
 

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OSG also make the sub-floor adhesive. HD sells it in the big tubes in case lots. Just used a case to install bead-board in a bathroom. The stuff will make you high so be sure to have ventilation unless you want a flashback to the 60's....wow man.
 

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BIGmouthinDC wrote
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OSG also make the sub-floor adhesive.
Beware that most floor adhesive isn't strong enough to hold a wall without screws. It's designed to work on floors without the lateral constant tug of gravity. Aparently Liquid Nails For Subfloors is strong enough to keep a wall from falling on people a couple of years later. Although if you crank the subs to 140db I'm not making any guarantees it'll last the week.


I didn't know what bead-board was, so I looked it up. It's a thin wood with vertical slats. I suspect that gypsum is heavier.
 

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Yes the bead-board is feather light and I only brought it up in the context of the odor.

.


As for the different glues. In my opinion any good construction adhesive is probably strong enough if you put on enough of it and use at least 5 big zig-zag lines of 3/8 bead running the length. (about one big tube per sheet) If you ever have to remove something that has been construction glued to a drywalled wall or ceiling you'll discover that the glue is not the weak link. It's the adhesion between the paper layers covering the gypsum. The paper tears before the glue will let lose.


Therefore the important aspect is to get as much coverage as possible.


I understand the thought behind the semi-rigid nature of the liquid nails brand. Next time I'm at HD I'll check the ingredients of the LN brand versus OSG. I remember now picking the OSG sub-floor product because of it's superior tensile strength and moisture resistance for my layered ceiling. It's still there.
 
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