3 layers of drywall, one layer of green glue. What layer?

[Pure L]

My inner room will be 3 layers thick (5/8"). My outer layer is 2 layers in the typical, between-stud, "beef-up" style.(8 inches between drywall.)

Within the inner, 3 layer thick wall I'd like to put green glue.

Is there a preferred layer in which to apply this?

I'm thinking that putting it between layer 2 and 3 would be best. I have no good reason for that, however. (Perhaps something to do with the power of 2 layers of 5/8"?)

Thanks.

[Soundman2020]

I'm not sure that it matters! Interestingly, the GG web site does not show testing results for your situation (3 layers of drywall, one of GG). It only shows 3 x drywall + 2 x GG, and curiously enough it even shows one with FOUR layers of drywall and only two of GG, where those two in between layers 1-2, then in between layers 3-4 (nothing between 2-3).

So probably it doesn't matter, but to be certain maybe you should contact them directly, and ask what they recommend?

One option might be to go with their own recommendation of 50% coverage, but do that in both 1-2 and 2-3, instead of 100% coverage for just one of those?

- Stuart -

[Eric Best]

Email Green Glue and ask them.

[britune]

You could also call the Green Glue Company. Their phone number is on their web site. I called them a couple times during my project. They gave immediate answers and were very helpful. They even answered questions about isolation that were not about their products. Great company!

[Pure L]

Thanks for the responses, all.

I actually got in touch with Sylvain at Green Glue and got his permission to post this here:

I think you can put GreenGlue either between 1 and 2 or between 2 and 3 for about the same result.
I may have a very short preference for applying it on the inner layers (so that the layer in contact with the studs is actually damped), but we are talking about very-fine tuning here (the difference is likely to be minimal)...

What is for sure is that I would not recommend to split it between the two interfaces. The reason being that the final thickness of your interlayer (directly related to the quantity put on each board) does matter quite a bit in order to get the optimal final performance.

Hope it helps.

Best regards and enjoy your room within a room!

Sylvain PAYOT

Good to know.

I should add that I wrote to Green Glue and received a response within 35 minutes of sending my email.

Tight ship!

[Soundman2020]

Great! They sure do seem to be a responsive company with a good product. (Now if only they could get their prices down a bit... )


- Stuart -

[xSpace]

"What is for sure is that I would not recommend to split it between the two interfaces. The reason being that the final thickness of your interlayer (directly related to the quantity put on each board) does matter quite a bit in order to get the optimal final performance."

Could you clarify what was the question you asked in order to get this response? Are we talking about adding 50 percent to the outer leaf and 50 percent to the inner leaf?

[Pure L]

Good catch, xspace.

Here's what I asked:

I'm looking to use green glue on my upcoming build (room within a room).

The inner room will be comprised of 3 layers of drywall.

I'm wondering where the most efficient/effective application of green glue would be?

Between drywall layers 2 and 3? 1 and 2?

Perhaps a mix? (i.e. 50% applied between both layers 1 and 2 and 2 and 3?)

The bit about "a mix" was inspired by Stuart's suggestion above.

[Soundman2020]

The bit about "a mix" was inspired by Stuart's suggestion above.

I was a little surprised with their answer, since I seem to recall that their own recommendations say that you can drop from 100% coverage to 75% or even 50% without too much change in effectiveness, so I thought that 50% coverage spread across two "interfaces" would be better than 100% on just one. But I'm sure the manufacturer knows his product!

Just goes to show that sometimes assumptions about acoustics just don't pan out. You live and you learn!

- Stuart -