John Sayers' Recording Studio Design Forum

Is Everflex AC50 used in the same way as green glue
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Author:  stusiod [ Sun Apr 08, 2018 12:25 am ]
Post subject:  Is Everflex AC50 used in the same way as green glue

I just ordered a few tubes of Everbuild Everflex AC50 as acoustic caulk.
But reading the label it mentions that it’s also a glue to put drywall up, which stays flexibel after curing.

Isn’t that the same as what green glue does or am I missing something?


Author:  Soundman2020 [ Sun Apr 08, 2018 2:18 am ]
Post subject:  Re: Is Everflex AC50 used in the same way as green glue

No it's not the same. Not even close.

This point comes up regularly, probably due to the misleading name "Green Glue". It isn't glue! It is not an adhesive, and cannot be used to "stick things together". In fact, it is designed to "keep things apart"! Green Glue is a constrained layer damping (CLD) compound, that is designed to create a thin acoustic damping layer in between two sheets of "something", such as drywall, OSB, MDF, plywood, etc. It is a visco-elastic polymer, not an adhesive. Yes, it is a bit sticky, and yes it does "adhere" to surfaces, but it's entire purpose is to prevent those surfaces from touching each other, and to hold them apart, by interposing it's own unique structure between them (as well as creating some thin air "pockets"). It is an acoustic product, with very specific properties. It is NOT glue, and it is NOT caulk. In fact, the Green Glue company does also make caulk, which is an entirely separate product from their mainstay, the "Green Glue Compound".

No, there are no substitutes. A few other manufacturers have tried to create other products that so the same thing, with various degrees of success, but nothing is fully comparable to Green Glue.

It's also not a good idea to glue drywall sheets together in any case! (Except with Green Glue, which isn't glue....)

Here's a direct quote from Rod Gervais' book on studio construction:

When two pieces of drywall (for example) are joined together through the use of conventional construction adhesives, they bond, forming (essentially) on thicker piece of material. The effective isolation created from this type of assembly is less (as a whole) than the sum of the individual sheets themselves.

Thus, by glueing sheets together (using standard adhesives), you decrease isolation.

But with damping systems, the bonding actions that take place with conventional adhesives never occur, and the isolation is (potentially) greater than the sum of the two sheets themselves.

Yup. Exactly. For detailed technical details of why gluing is a bad idea, read the famous Wyle Report. Way old, but still very true.

- Stuart -

Author:  stusiod [ Sun Apr 08, 2018 3:05 am ]
Post subject:  Re: Is Everflex AC50 used in the same way as green glue

Thank you so much Stuart!

I was googling this a lot and couldn’t find any good information!
I’m happy you took the time to clear things up!

I have another question regarding sound traveling along a wall from one room to another.
Do you have any resources on sound traveling along a 60cm thick solid stone wall from one room to another? The sound traveling through the wall isn’t an issue in my case because there’s only a field behind the wall.


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