Would you rather glue or screw?

Now that I have your attention... I am a little confused about something that I read in Ron's book, which I can hopefully get cleared up as I have drywallers showing up tomorrow to do some work. In Chapter 4, Damping systems, he notes" the effective isolation created from gluing multiple sheets together is less as a whole than the sum of the individual parts, which makes perfect sense (i.e. a 2" thick piece of drywall, if there was such a beast, would be better than 4 @ 1/2" pieces glued together). The next line he says "Thus, by gluing sheets together (using standard adhesives), you decrease isolation". He is talking about damping systems, so I am sort of taking this out of context. The part that I don't understand is: Am I better to glue 4 sheets of 1/2" drywall together to form one side of the mass or should they not be glued (i.e. rather screwed together instead). I actually plan on gluing or screwing (depending on the responses) the first three sheets and then "Green Gluing" the 4th sheet. I am using 1/2 because I was given a lot of it for free so I am just increasing the number of layers for the mass. Thanks, Danny

Rod pointed out to me personally, many months ago, that it is better to not use construction adhesives to glue sheetrock panels together. I am not boasting here either, just repeating what I was told and soon read up on. But the text you are presenting is saying that same thing. It may be in the damping section, but those specific parts that refer to glue are talking about construction adhesives and that using them in this case will not benefit you. I have the document that addresses this issue specifically but cannot get my finger on it directly. If you would like it, and have 24 or so hours, I can find it. Of course, I have no way of knowing what it is you are doing and what you are loading up with 4 sheets of 1/2 inch rock. Be safe, Brien

Thanks for that. I am actually placing the drywall mass into the joist space above my garage to create the first leaf of my MAM (ceiling in this case). So I guess that I should screw (no glue) the 3 sheets to the underside of the floor sheathing within the cavity, incl caulking, etc. between each layer at the edges. Then I was planning to do the last layer with green glue and use a 5/8" sheet there. Then air space and 2nd ceiling for the studio.

Am I better to glue 4 sheets of 1/2" drywall together to form one side of the mass or should they not be glued (i.e. rather screwed together instead).

Like Brien said, don't glue them, just screw them. Green Glue is not really glue at all, so maybe that's what is confusing you? GG is not meant to be an adhesive, and does not count as glue, for what Rod was saying. GG is designed to damp and absorb acoustic energy between the sheets of drywall, whereas normal construction adhesive does not do that. Rod is talking about construction adhesive there, I think. From what I understood of what you are saying, this is just for beefing up the underside of whatever is above you, in strips between the joists? If so, then I don't think GG will help you much there, as the drywall will be in little chunks. I thin I'd save the GG for use on the large surface area of full drywall panels that go on your inner leaf. That's what it is designed for. I think you'd be better off with just screwing or using cleats to hold your drywall "beef" up between the joists, and caulk each layer all around the edges for a good seal. At least, that's what I've seen recommended around here. - Stuart -

boogiedude wrote:

I am a little confused about something that I read in Ron's book, which I can hopefully get cleared up as I have drywallers showing up tomorrow to do some work. In Chapter 4, Damping systems, he notes" the effective isolation created from gluing multiple sheets together is less as a whole than the sum of the individual parts, which makes perfect sense (i.e. a 2" thick piece of drywall, if there was such a beast, would be better than 4 @ 1/2" pieces glued together).

First - my name is Rod - not Ron. 2nd, your i.e. is wrong - I meant exactly what I said - the effective isolation created from gluing multiple sheets together is LESS as a whole than the sum of the individual pieces. i.e. - a 2" thick piece of drywall (if there was such a beast) would be worse than 4 @ 1/2" pieces glued together.

The next line he says "Thus, by gluing sheets together (using standard adhesives), you decrease isolation". He is talking about damping systems, so I am sort of taking this out of context.

This is consistent with my earlier statement.

The part that I don't understand is: Am I better to glue 4 sheets of 1/2" drywall together to form one side of the mass or should they not be glued (i.e. rather screwed together instead). I actually plan on gluing or screwing (depending on the responses) the first three sheets and then "Green Gluing" the 4th sheet. I am using 1/2 because I was given a lot of it for free so I am just increasing the number of layers for the mass.

You are never better off gluing it together - use green glue or not - but never glue (laminate) sheets together. Rod

Sorry about the name, that was a typo on my part. And thanks for clearing up my comments. I now understand exactly what you mean. I had the drywallers there today and we placed the mass layer between the joist spaces. The drywallers were excellent and managed to fill each joist cavity with layers consisting of single pieces in each. Of course they made me do the caulking, which I wanted to do anyways to make sure it was thorough and complete throughout. Also, I did use green glue between the last layer as is was placed as a single piece of 5/8 " and there's bedroom is above. I figure that this would help even if only a little. I also want to thank everyone so far. This forum and Rod's book have been invaluable and have saved me from those typical misconceptions that I would have expected to be true regarding sound isolation and from making those same mistakes which would have essentially rendered my room useless.