hacked sheetrock on a wall

jwl · Post by **jwl** » Sun Apr 02, 2006 2:44 pm

Greetings all, currently my studio is in a 15x17 room in a basement, 2 walls are unfinished concrete covered by foam insulation panels, the other 2 are framed 2x4s with one layer of sheetrock. These walls have 2 doorways cut in, with no doors installed just yet; I plan to use the hollowcore door reinforced by MDF plan for those.

The sheetrock that is installed on one of the walls was a hack job using drywall scraps that are literally fit into place like a jigsaw puzzle. Pretty far from airtight, lots of seams some of which aren't precise (say, up to a 1/2" wide). Eventually I plan to have at least 2 layers of sheetrock on these walls, so my question is this: should I leave these "puzzle pieces" (none of them are bigger than 2'x2') in place and just put new sheetrock over it, or should I just rip them off and replace them with unbroken sheets? If I leave them in place, should I caulk up all the joints? I will probably buy enough sheetrock for 2 layers, I can either put the 2 layers over this quasi-layer making 3 layers, or just rip this down and have 2 layers of unbroken sheetrock.

Some amount of isolation is the goal here, I will sometimes put an amp or a singer on the other side of this wall while tracking for isolation. I realize I'm not going to get a ton of iso however, and that's OK, I just want to know the best option here.

Sandersd · Post by **Sandersd** » Sun Apr 02, 2006 2:47 pm

Rip 'em off, please.

jwl · Post by **jwl** » Sun Apr 02, 2006 3:05 pm

OK, but why? Inquiring minds want to know....

SonicClang · Post by **SonicClang** » Sun Apr 02, 2006 3:30 pm

I don't totally see a real reason you couldn't mud what's there and put your two layers on top of that. Even if it's not sealed, it's still mass. But if you're planning on putting resilient channel on the studs and screwing the two layers of drywall onto that, then definitely take down the hack job drywall because that will add another leaf to the wall which will mess up its sound stopping abilities. If you screw the two new layers directly onto the hack job drywall, then all three of those layers become one leaf.

jwl · Post by **jwl** » Sun Apr 02, 2006 3:44 pm

Hi Sonic, that's precisely what I was thinking. Mass is mass, and with enough mud....

I wasn't planning on using RCs. Simple is good, and the extra bit of iso probably isn't worth the headache.

My concern is this: on one hand the hacked drywall is mass, and as you say, mass is mass. On the other hand, I don't want each individual piece resonating at its own frequency or anything.

All things being equal, I'll probably just mud over it and slap the next layer on top unless I hear of a good reason to remove it.

SonicClang · Post by **SonicClang** » Mon Apr 03, 2006 1:35 am

Use glue to adhere the crap to the new. That should hold it all together.

It's totally up to you though. I can say though that when we were skinning our walls with OSB, we never bought a bit of it, we scavanged it all from homes that were being built in my neighborhood from the dumpsters, and some of our walls looked like hack jobs. But for us, mass was mass, we didn't care. Two layers of drywall were going over all that so no one will ever see it.

knightfly · Post by **knightfly** » Mon Apr 03, 2006 3:53 am

In the end, each piece won't resonate at it's own frequency; that's a function mainly of THICKNESS.

The downside of leaving what's there is the possibility of having successive layers' joints line up; but if it's a choice between two full-sheet layers or two full-sheet layers PLUS the scraps, I'd leave 'em. Just do a thorough mud/tape/sand before the next layers go on.

You do not, however, want to GLUE anything; when you glue two layers of drywall together, you create ONE layer of thicker drywall that has a LOWER coincidence frequency; this is one of the frequencies that gets thru the wall easiest. When you lower this coincidence frequency, you make your wall about 6 dB WEAKER at that coincidence, because of mass law - mass law causes a wall to improve by 6 dB for each octave HIGHER in frequency, so by keeping your individual layers INDIVIDUAL (but not separated by air) you cause this 6 dB loss to happen an octave higher, where it's less of a problem - it's the LOWS that're hard to kill, so we don't want to weaken the wall at lower frequencies if we can help it.

This is not to say that this weakening effect will happen when using something like Green Glue, which isn't really a glue at all; it's a Constrained Layer Damping material, which is an expensive but effective, whole other ballgame... Steve

jwl · Post by **jwl** » Mon Apr 03, 2006 4:14 am

OK, thanks knightfly. I'll plan to mud and tape this hacked area, and then just put more sheetrock over it WITHOUT glue. Thanks so much for the explanation.