Need Green Glue btwn Sheetrock & Sound Board??

[rungriot]

Hi Everybody,

I am in the process of building my H/T in the basement and am using 1/2" sheetrock w/ 1/2" soundboard on the walls but 3/4" sound boardfor the ceiling. This is additon to putting up insulation btwn the floor joists as well as btwn the studs. My question is whether or not I need to use a product like Green Glue between layers or if I can just put them up one atop the other? Also, is it advisable to stagger the joints or can i just calk the in-betweens? Any help is greatly appreciated!

 

[Johnd]

Hey rungriot:

1) Always stagger the joints;
2) I would recommend 5/8" rock, at least for the top board; and,
3) Yes, green glue provides some isolation for noise reduction.

Cheers.

 

[bpape]

Save your money and get better performance. Use Green Glue between 2 layers of standard drywall.

Bryan

 

[rungriot]

thanks guys. i will make sure to stagger the joints as suggested. i was able to find 1/2" x 4' x 8' sound board for $9/panel - which is comperable to the mold and mildew resistant sheetrock i am putting up so i figured it was a good way to go. the green glue is kinda pricey - the cheapest i found it for was $14 a tube and the recommended amount is two tubes per panel. oh well, guess it'll be worth the couple of bucks it costs in the end.

 

[kiwiaudionut]

Quietrock 510 is apparently available for about $45 a sheet. It is the cheapest member of the quietrock family, but has stated STC's in the lower 50,s comparable to Green glue.
After purchasing the two sheets of drywall necessary to make a GG panel, your cost is similar, but without the glue application labor.
My problem with green glue is its application. If you watch the videos, they apply it from the tube in a haphazard manner and it does not get troweled. I don't see how a uniform layer can be attained in this manner - but it apparently works !
I'll be choosing one of these methods myself, i'm just not sure which one !

 

[bpape]

GG is not cheap - but it performs well and as advertised.

When comparing the 2 products, look at more than the STC. Look at the actual test data and look at the isolation at all frequencies - especially the lower bottom end where STC doesn't sample.

Bryan

 

[kiwiaudionut]

Hmmm - The GG does seem to have a better transmission loss in the lower frequencies, which is surely the most important area.
You've done your homework Bryan - good job!

I can't get the GG application process out of my head though. I'm thinking a toothed trowel after the random caulk gun application would ensure a more uniform coverage and a better sandwich filling !

Ived used a caulk gun all my life and have never seen uniform coverage using the haphazard approach described.

 

[bpape]

Hundreds of people have done it using the 'looks like spaghetti' random method. Just remember that this flows a bit more than caulk would so it's easier to just kind of drizzle it around. Plus, with 2 full tubes per 32 sq ft sheet, it's not hard to get decent coverage that the pressure of being screwed together will spread it out.

In all honesty, I had a customer who tried to do the notched trowel thing - he ended up with a mess on his hands.

Bryan

 

[kiwiaudionut]

Ok Bryan, you have convinced me on the Green Glue, and probably swayed me from trowelling also, excepting that I just love to make a mess!!
I wonder if you would be kind enough to elaborate on some installation details/tips/tricks? Your idea with the heat duct box is already taken to heart. I'll be doing that with the cold air return also.

I'm wondering what product you use around the perimeter of the drywall sheets as they butt together on the wall. I think SIC talks about an acoustic caulk in their spiel about quietrock installation- is that overkill, or is standard caulking good enough?

Instead of making a drywall sandwich with two sheets GG'd together on sawhorses, then applying that to the studs, would it be preferrable to drywall in a standard fashion then GG and lap the prior joints. I think the latter sounds like a better idea !

Is there a benefit to laying a bead of caulk directly to the studs prior to drywalling?

My ceiling has a layer of 5/8 drywall on it already, and the walls have 1/2" that in some cases I'll be pulling down and starting over. I can access the end cavities in the ceiling from the adjoining room so I was considering GG and another sheet directly on top of this and blowing insulation into the ceiling cavities. Is this OK, or is batting superior insulation? This ceiling cavity is 10+ inches, so I can cram a lot in there!
The ceiling is important to me as the master bedroom is directly above it. The Missus should not be disturbed as her wrath holds no bounds !

I really appreciate your help so far, and also for anything else you may add,
Kiwi.

 

[bpape]

Acoustical caulk is specifically designed not to shrink over time. A good 50 year silicone caulk will do fine - but it's not very paintable and likely just as expensive as acoustical caulk - but you can get it locally.

DEFINITELY put up one layer of drywall with screws. Then drizzle the GG on the back of the next layer and screw it on the wall. Much easier. and the seams don't line up that way (VERY important).

To do it right, start with the ceiling. Then do a wall, then move around the room clockwise or counter - matters not. THEN go back and do the ceiling again, then repeat the walls in order. This makes the corners seams a double Z shape instead of a straight line for sound to get out. It has to hit mass and turn 3 times to escape. As I said earler, don't line seams up between layers. Make sure a seam on the 2nd layer is in front of a middle of a sheet on the 1st layer. This is very very important.

Blown in cellulose is fine in the ceiling. As for the rest, do the whole thing or don't bother. A wise man once made this analogy about a sound room and sound transmission:

"Imagine your room is an aquarium. If there's a hole or a weak spot, it doesn't matter where, you're going to get wet!"

Doing just the ceiling and allowing the sound to flank through the weaker walls, outlet openings, under walls, under and through doors etc. and into the next room (or a gap between the wall and the concrete) and up to the floor above is a waste of time and money. It will help a little but not nearly as much as if you pay attention to the details.

Add up all of the holes in the room and look at the square footage involved.

Bryan

 

[rungriot]

bpape - thanks for the detailed explenations. i printed your last post and am going to show it to my GC to use when he starts closing up the walls