Green Glue questions and answers

I had a couple of questions regarding the use of the Green Glue product which I posed to them directly. Their responses have been impressively prompt and informative, and I thought I would post them here for the benefit of others. Below is a somewhat abbreviated email exchange with them: I'm not clear on one point. When used on a sheetrock wall, in between two sheets, are you saying that you screw the two sheets together after application? If so, why doesn't that negate the effects of the Green Glue, as you have now made the sheets "as one"? Thanks in advance for your response. That's a really good question. Green Glue doesn't function by mechanically seperating the layers of drywall, it functions by converting mechanical vibration into heat (its a viscoelastic material). When sound passes "through" a wall, the mechanism is sound vibrating one side of the wall, this vibration transmitting as sound through the air cavity in the wall or mechanically through the studs, and then vibrating the other side, which radiates new sound into the next room. With Green Glue in the assembly, mechanical vibration is constantly being converted into very small amounts of heat, resulting in less sound transmission. At resonance points, where walls tend to bleed the most sound, GG is effective in the same manner. The stored resonant energy is dissipated as small amounts of heat. OK, and I'm with you on the effect of viscoelastics dissipating the energy as heat. But where I connect the two layers of drywall via a screw, it would seem that gives a direct path from one board to the other for the vibration (through the screw). Is it that this represents a negligible amount of energy coupling, and a necessary compromise in order to physically mount the board? Or maybe I am missing the bigger picture. Is it that the combination of board, Green Glue, and another board become a complete damped system acting as one but with much less vibrational characteristics than the same assemby without GG? Side question: One thing I don't remember seeing was how many screws are typically required to fasten two 4 by 8 sheets together. Thanks for your assistance in this. I just want to make sure I understand before investing what appears to be a considerable amount in my studio. I can't argue with the accolades, both on your site and elsewhere. But I just wanted to get straight in my head exactly how to do it, and why and how it works. With a material like GG, or a rigid adhesive, or even no adhesive at all, the two drywall layers aren't decoupled, but rather coupled (by physical contact with no glue, or adhesion with the adhesives). You said:Is it that the combination of board, Green Glue, and another board become a complete damped system acting as one but with much less vibrational characteristics than the same assemby without GG? And that is exactly it. Its not decoupling at all, but rather just a less resonant / less conductive (for vibration) assembly. Generally normal building code calls for screws to be 12" on-center for 24" stud spacing and 16" on-center for 16" stud spacing, and thats what we test at. The first layer needs jsut minimal screws to hold up the board (perhaps 24" on-center). Its never a bad idea to ask the local building inspector what local code is.

Thanks for sharing. The company has a lot of integrity. I can personally vouch for the product. You raise an intresting question about the screws- I can tell you from experience you will NEVER be able to pry two pieces of drywall apart that have been GG'ed together- after curing for a couple days. Hmmm...I wonder if they have ever tested a wall without screws.... Even if it did perform better, it would be illegal for them to recommend not using screws. I guess one could remove the screws after the GG had cured, but the screws are going right through the mess, too, so they may not come out so easy... but I would never attempt that on the ceiling. My guess is the difference in performance is not significant enough to compromise personal safety.

studio_drums I applied it on a floor, without any mechanical connection (wasn't possible there). And I discussed it personally on the phone with Brian (the designer of GG, also responsible for these numerous tests and measurements). He honestly told he couldn't guarantee anything, and was interested in the outcome of that experiment (which it was). I also made sample test pieces (which I still have on my desk) to see how GG behaves over time. I could disconnect layers manually (on small pieces) even after many months if I wanted, but not easy. I can still manually offset these small pieces of boards somewhat. If I should wrickle with a kitchen knife they come apart again. :finger: And it's still as sticky as it was after a couple of days, a week and a month even the parts where GG is exposed to the air in standard ambient in-house conditions. These screws/nails wont matter that much since we're not speaking about decoupling but suppressing the vibration. The contact between the panels and the wooden studs themselves is much more defining than these point contacts of screws. The main limiting factor of such a wall remains the location of the MSM (:) GG can suppress resonance/vibration, but not alter physics). Now the necessity of screwing the panels (beyond safety reasons) is very simple: You can't press these boards together during curing time (which is very long) and spreading out this GG stripes as coming out of the tube on the board (they become devided over the surface by this pressure resulting from screwing the boards together). Hence this screwing helps the application. It should be a nightmare without. In order to do my floor. I had to make something to apply pressure between ceiling and floor, just to make up for this lacking mechanical fixing. Made the whole thing much more complicated. Lucky that was a relative small floor.

Eric, Were your sample pieces made of drywall? I've had 4" diameter holes and some other 8x10 pieces of drywall cut out and they cannot be taken apart without breaking up the drywall. Interesting... I understand the necessity of screwing the panels togther. What I was proposing was screwing the panels together and then removing the screws AFTER the GG cures. Ironically I did my own experiment two days ago in an attempt to duplicate my proposed interior wall build. You know- just for reassurance. I had (6) 2' x 4' pieces of 5/8" drywall. I glued 3 pieces together, laid them on the floor and stood on them for about a minute. Then I lined up the edges again, because of course they were sliding a little. I let this sit for a day, then compared them to the other 3 pieces just held tightly together. If you rap your knuckles on the GG'ed drywall it feels like a cinder block wall- but with no resonance. The difference is profound. I don't think the screws make much of a difference- partly based on their documented testing "shorting out" RC's purposely. Maybe not a direct comparison but...

My samples: Different kinds: drywall, solid wood, fiber board ...... The real effect of GG you notice only completely after a month or so. It's strange .... I even made fun of that with Brian, telling a possible 15/30 days: "if not pleased we'll pay you back" guarantee was too cheap from them, since the curing time takes that long. Therefore I also asked how they did such measurements in a lab, since blocking a lab for that long for every measurement should cost fortunes. Hence they have to prepare these panels somehow beforehand. A story: An old building (+/- 100 years). Destructive testing not allowed, or to be avoided due to architectural value and limitations. Nobody has an idea about the exact structure. I have a ceiling with some strange extremely hard board (looks like cement board, but how old?). When I knocked on it, that ceiling and a lot with it starts singing at +/- 42 Hz: BOOOOOIIIIIIIIIIIIIIIIIIIIIING. I don't want to demount that ceiling. Some small drilled holes and testing showed a very large cavity (around 50 to 60 cm, at least on the tested spots) without any absorption. No idea if that cavity went much further than the boundaries of that room (it went further on 2 sides, but how and where, and outside drilling holes was no option). We felt joists, but couldn't imagine well how that construction was build. I wanted to test GG here, not sure (even partly believing) it could help me out here. Hence we searched for joists within the room boundaries, and mounted one 12.5 mm gypsumboard with GG. About 7 to 10 days later. I knocked on that (high) ceiling. It was a bit better but still: BOOOIIIIIIIIIIIIIIIIIIING. I thought "damned, not worth the trouble and energy", searching for another way. 1 month later, I tried again, just for the fun of it, and because others told me they had the impression it was improved. There was no way anymore I could trigger that resonance (and I really tried). The result: BOING.

A very telling story, Eric. I guess patience is a virtue with this material. Incidently, the email exchange from above was in fact from Brian. He seems to be a most likeable chap, and honestly seems to enjoy the opportunity to communicate about his product. This is a welcome change from the similar (but detectably different) run-of-the-mill sales rep.

I emailed this question to Brien and this his response: Have you ever tested a partition wall without screws? Or after removing the screws once the Green Glue has cured? I'm curious what the difference in performance is with screws vs. no screws. "We have mess around with removing screws in tests. What we've found is that if you lessen the number of screws holding the drywall to the studs, you do get some benefit as it becomes less coupled. It is also no longer very attached to the studs which is not a very good idea. If the first layer is screwed to the studs removing screws from the second layer won't have much effect. Did this answer your question?" Hmmmm... To me, it makes logical sense that since the subsequent layers of drywall will be screwed into the studs also, that this will also serve to increase coupling to the walls. Right? Is he saying that there were diminishing returns? Whether its 12 or 36 screws the wall is coupled just the same?

studio_drums wrote:

Whether its 12 or 36 screws the wall is coupled just the same?

:twisted: I wonder what 24 screws should do .......... Was Brian discussing a common stud or staggered/double studs? Further I think that a simple felt tape (when having a common stud) between boards and stuts will make a difference. I think the screw in itself is less defining than the pressure of the boards against the studs by these screws (but can't prove that).

I have just finished putting up all my second layer of sheetrock using Green Glue, I over ordered big time I have 5 c/s left over. I have a bunch of Auralex foam isolation that I am going to put on the ceiling, Can I use the Green Glue to install it? Thanks, Clifford.

Eric_Desart wrote:

studio_drums wrote:

Whether its 12 or 36 screws the wall is coupled just the same?

:twisted: I wonder what 24 screws should do .......... Was Brian discussing a common stud or staggered/double studs? Further I think that a simple felt tape (when having a common stud) between boards and stuts will make a difference. I think the screw in itself is less defining than the pressure of the boards against the studs by these screws (but can't prove that).

We were talking about multiple layers on a single stud. Wow...sounds like you endorse the ASC Walldamp concept...I was actually considering putting green glue on the actual studs as well....but too late! My first drywall layer is on and seems to be working great (per my studio build thread) even before I apply two more layers with green glue in between...

natas wrote:

I have just finished putting up all my second layer of sheetrock using Green Glue, I over ordered big time I have 5 c/s left over. I have a bunch of Auralex foam isolation that I am going to put on the ceiling, Can I use the Green Glue to install it? Thanks, Clifford.

No you can't GG is not a glue unlike the name suggests. (you should know by now) meanwhile you can send the GG leftover case to my home address :twisted:

Here's Brent's response from GreenGlue: It is contrary to logic, but Green Glue doesn't work by decoupling the layers. It works by stopping vibrations in the sheets. By removing screws in the first layer, you do get some decoupling from the studs similar to using say resilient channel.

studio_drums wrote:

Wow...sounds like you endorse the ASC Walldamp concept

studio_drums, Do we misunderstand one another? I wasn't referring to anything like ASC. Just before screwing your first layer to the studs, having some thin cheap self adhesive felt stripe against the studs. One of the ugly things by screwing gypsum board to a common wooden stud is the structural resonance caused by these studs themselves (with thin gauge metal that's better). I'm rather sure that a small felt stripe (which doesn't cost much and easy to apply) can help here. As said (and I assume/guess) it's more/lots the pressure of the boards themselves to the studs causing this, than the point contacts of the screws themselves. It cost little and is little additional work ......

http://www.asc-soundproof.com/wd-sssp-1.htm We understand each other fine.