Fastening Drywall

Hi all, We'll as we beging the tear-out of the old drywall in my studio, my contractor and I have been talking about methods of attaching the two layers of drywall to the walls and ceiling. I'm pretty sold on the flexible RC1 channels, but my contractor has never used them. He's concerned about two things: 1. The weight of two sheets of drywall hanging from the RC1 on the ceiling. 2. That the inherent design of the RC1 won't allow for a nice finished product. He's afraid there may be some bowing. He's proposing that we do the following: 1. Put down a layer of flexible caulk on the studs and joists. 2. Attach a rubber material, about 1/8th thick. 3. Put down another layer of caulk. 4. Put down another layer of rubber. 5. Put down a third layer of caulk. 6. Screw the drywall to the studs and joists - through the two layers of rubber. I'm concerned that sound transmission will take place through the screws, but he believes the rubber will dampen all the vibrations. I should say that the contractor is a friend of mine who does INCREDIBLE work on full basement re-models. He's VERY quality consouse [sp], and he's donating his time so he is not trying to screw me in any way. He just wants the project to be the best it can be within our constraints. I think he also shies away from no-brainer commercial solutions such as the RC1 because often knows of better ways to achieve a desired affect than by using a mass-market off the shelf product. Seeking some guidance (still)... :) Thanks all - the tearout begins this week!!!

Tell him Rc is ok. I hung 2 sheets 1/2" Drywall and 1 sheet Celotex from rc channels. there are some basic spacing specs 916" oc) for spacing the channel to maintain it's strength. the bigger issue is making sure your screw through the drywall and into the channel :) Ok maybe not so big.

giles117 wrote:

basic spacing specs 916" oc) for spacing the channel

WOW that one hell of a gap!

RC is fine for ceiling. RC is actually designed to use on ceiling to help "level" it. As you know, joists and wood usually bow, so RC actually levels the drywall. Read the USG manual "sticky" at the top of the forum. The rules for spacing, and size of screws, etc is all listed there. Aaron

Yep - tell your contractor not to worry. RC1 + layers 5/8 drywall is perfectly fine on the ceiling. It will not fall down and it will look excellent - no bowing or anything like that. The caulk / rubber solution will really be a waste of time because the screws will still be going through the drywall and into the joists. Here's a photo to show your contractor that the ceiling will come out looking good

Everyone has given good advice so far - have him use lots of masking tape markers, and mark positions of EVERYTHING in the construction - studs, joists, conduits, etc - no wall that intersects with another wall or ceiling should have ANY wallboard surface in hard contact with its intersecting surface, nor should any piece of RC come closer than an inch of the intersection. Mark the locations of all the strips of RC and run them straight and true end to end, so that you don't miss with any screws; mark stud locations so you do NOT put any screws through the wallboard and RC and into a stud, just in case the screws might be long enough to touch the stud. Leave your 1/4" gap all around the perimeter of each wall surface (not between sheets of wallboard on a given wall, though) - use spacers to keep this gap. Caulk these perimeter gaps with acoustic rated caulk/sealant. \ If in doubt about ceiling support, get specific information from the manufacturer of the actual RC you're using regarding spacing of the channels, for the EXACT amount of panel weight you'll be using. RC is for all intents and purposes a "spring" - and just like a spring, it needs to NOT be at either end of its "travel" if it is to act as a spring. The manufacturer will know their specific product's characteristics better than anyone, so their spacing recommendations should be taken over anything you read in the USG manual - USG, as I understand it, no longer makes RC; and those companies who do, may have changed things like gauge, perforation ratio of the resilient leg, etc - Use proper screws for each application - screws for wood when attaching RC to wooden framing, screws for steel when attaching wallboard to RC or to steel studs, etc - for all but top layers, you can use half as many screws (twice as far apart) as standard, then the top layer gets a full schedule. Longer screws for successive layers, always at least 3/8" longer than total material thickness, 1/2" longer is better (but watch placement, as I mentioned above) Do NOT, repeat NOT, let your friend put up a course of wallboard and THEN use RC and more wallboard - I've talked to a lot of experienced contractors who've claimed RC didn't work, and without exception found that they had NO IDEA of the physics involved and had put the stuff in the wrong order. Hope that helps, if your guy has any more questions or doubts now's the time to clear them up, not AFTER... Steve

THANKS everyone - I really appreciate all the help! Steve:

Do NOT, repeat NOT, let your friend put up a course of wallboard and THEN use RC and more wallboard

This leads me to a question. We're going to do it as you said on the other three walls. I have one wall that is a concrete block with about a 1/75" foam layer and then a layer of drywall. What do you recommend for this wall? Could we use mollies and attach RC right to this and then just add one more layer of drywall?

Take Knightfly's great advice on the masking tape - it seems like a small point but once you've got a few sheets of drywall up (and especially when you are on the 2nd layer) - you'll be cursing if you don't know where those joists are :( One thing I found useful was to place the shims on the wall exactly where the joists are.

"1/75" foam layer and then a layer of drywall" - confused here - do you mean .750" (as in 3/4")? If the foam is closed cell it probably wouldn't be too bad - if there's room, you'd be better to put up a separate frame to get 3-4" of air/insulation space (NOT foam) and then the wallboard, no RC needed with the separate frame. Fastening into foam and wallboard won't hold much weight, we probably need to discuss this more... Steve

I believe he said 1.75" foamboard. I'll verify with him - I may have this wrong...

AndrewMc wrote:

Take Knightfly's great advice on the masking tape - it seems like a small point but once you've got a few sheets of drywall up (and especially when you are on the 2nd layer) - you'll be cursing if you don't know where those joists are :( One thing I found useful was to place the shims on the wall exactly where the joists are.

Good plan - thanks! I tell ya, I'm a bit nervous about the entire project. Beginning to think I'm insane. All I want to do is play my amp at night! I was feeling a bit guilty about spending the money and tearing things up for a month, but then my wife said "do you want to play through headphones forever?". I love that woman. :) I have a feeling this project is going to stress the hell out of me.

I think it's normal to be nervous the whole way through - especially when your $20K into it. A few fleeting moments of sheesh am I crazy - but I can tell you that when you crank that amp at 2am and you can't hear it outside you'll be loving it. The construction is not that hard - just take your time and make frequent trips to the beer store.

AndrewMc wrote:

I think it's normal to be nervous the whole way through - especially when your $20K into it. A few fleeting moments of sheesh am I crazy - but I can tell you that when you crank that amp at 2am and you can't hear it outside you'll be loving it. The construction is not that hard - just take your time and make frequent trips to the beer store.

"Looks like I picked the wrong week to stop sniffing glue" :lol:

Andrew, good call on placing the shims coincident with studs, thanks - also, I forgot to mention marking where each and every screw goes - again, seems too anal - but you'll reconsider the first time you try to put a second layer's screw through the head of an under layer's screw, and only end up tearing the crap out of your wall - Stone-man - 1.75" sound more like it; still, I'm wondering if you could stand to put up maybe a 1.75" steel stud frame (spaced maybe an inch from the existing) and a layer or two of wallboard there - no RC needed, because of the separation between outer and inner wall, and better isolation. When using NON-load-bearing, light gauge steel studs OR RC, the flanking problem caused by fasteners pretty much goes away because it's absorbed mostly by the insulation - but if fastening straight to wood studs on BOTH sides of a SINGLE frame, flanking from fasteners can cause as much as maybe 10 dB loss in isolation. Let me know if you can consider the second frame idea, or if you think that wall is already "good enough" - if that's the case, then maybe just another layer of wallboard. Keep in mind, though, that a completely solid heavy wall like that will also increase the need for more bass trapping once the room's complete... Steve

I would definately prefer not to do a new wall if I can avoid it. I plan on accoustically treating the room when it's done, ie. add bass traps, diffusors, etc. This will have to come later though. Do you think it's that critcal to add a wall? Would I need to tear out the foam and drywall first? Perhaps just adding a layer of 5/8" drywall on the outside might do it?

In that case I'd just add a layer of drywall - you could probably just use panel adhesive, and just strip-glue every 16" (like stud spacing) - this will avoid the new panel changing the coincidence frequency of the old by becoming "one piece"; if you just glue strips on spacing similar to studs, you maintain separate coincidence frequency for each panel and the wall has better isolation. Putting another layer on RC, with only 1/2" air gap, would give you a mass-air-mass resonance of around 200 hZ - this could become a real pain to fix with treatment later. The mass of the blocks and everything else should give you pretty good isolation as is, probably around STC 55 or so... Steve

Awesome info (as usual). Thanks! :)

Glad you likee :) was gonna post this link earlier and forgot; just when you thought it was safe to ask more questions... :wink: http://irc.nrc-cnrc.gc.ca/practice/noi1_E.html Enjoy... Steve

knightfly wrote:

Glad you likee :) was gonna post this link earlier and forgot; just when you thought it was safe to ask more questions... :wink: http://irc.nrc-cnrc.gc.ca/practice/noi1_E.html Enjoy... Steve

Wow, some of that was unintuitive - such as actually reducing STC if you don't do the drywall right. I'm losing me hair... :) I think we're glue a 5/8" sheet of drywall to the original drywall/foam setup, unless you have a better suggestion...

In this case, that makes the most sense. When you do, assuming you don't have ANY wetness in that area, I would put the new layer resting on 1/4" thick spacers , do NOT spread glue on the entire panel but only 2-3" wide stripes running the same as studs (2" stripes if you use 16" centers, 3" if you use 24" centers) - spread the glue stripes on the existing wall vertically, set the spacers directly under each stripe, then screw the new panels onto the old using Type G, or gypsum, laminating screws to hold the new panel against the old til the glue sets - after that, you can mud over the laminating screws, caulk around the new panel, and finish (tape and texture, etc) This will get you better isolation than full surface glue... Steve

Wetness has never been a problem. What do you recommend to use for the spacers? Oh, we started ripping out drywall yesterday - we're finally started! :)

If you have some 1/4" plywood scraps they're perfect - if not, you can rip 1/4" slices from a piece of scrap 2x lumber - the plywood is much easier if you don't have access to a table or radial saw, though... Steve

I've got a table saw - we'll get it done. Thanks. :)