John Sayers' Recording Studio Design Forum Archive

Hi,
I went through many posts on the "beefing up" method of adding mass to the underside of a floor between the joists.
The recommended method is to use wood cleats to hold the drywall in place.I was wondering why not just use screws to hold the drywall? It seems more troublesome to have to hold the drywall up and try to screw the cleats in.If I'm using 1" screws through 5/8" drywall, into 5/8" flooring, they wont go through the floor above. If I divide up the drywall into smaller pieces (12" x 16"), 2 screws should hold it, I would think.Or there an acoustic reason for the cleats?

Thanks.

If you screw it in place, then you force both layers to act together as a single, united, solid layer, instead of allowing them to work independently. It's almost as bad as gluing them together! If you caulk the edges and add cleats just to keep it in place, then you allow the drywall to act independently of the sub-floor above, as well as together with it, as a system. There are some frequencies where they need to act separately, and some where then need to act together. If you want to improve that even more, then add a layer of Green Glue in between. GG is a constrained layer damping material that improves isolation over and above the individual layers, by damping certain types of waves and resonances that occur in the "sandwich".

If I divide up the drywall into smaller pieces (12" x 16")

That, too, would be a mistake: keep the pieces as large as possible, to maximize the benefits. Of course, there are places where you'll have no choice but to use small pieces, but as much as possible keep them large. And always, ALWAYS caulk the joints between the pieces....


- Stuart -

Thanks for the quick reply!

So,it should be like this?
opps forgot the caulk in drawing... I'm thinking I could screw it into the floor, put in the cleats, take out the drywall screws and let the layers of drywall down onto the cleats and then apply the acoustic caulk. Seeing as I only have two hands to do it with...

Sort of... but like this:

opps forgot the caulk in drawing...

Yup. I fixed that for you, above.

I'm thinking I could screw it into the floor, put in the cleats, take out the drywall screws

... and then you'd have to carefully caulk the screw holes!!! ...

let the layers of drywall down onto the cleats

... and that would leave an air gap above!!! You cannot ever have any air gaps between layers in a leaf. Never.

Seeing as I only have two hands to do it with...

Do it like this:

Firsts, put your GG on the piece of drywall:
Then lift that up against the floor above, press hard, and tack in brad nails gently, sideways in to the joists, to hold the drywall in place temporarily:
Then caulk it all around the edges, take out the nails, then add the cleats (also tacked sideways in to the joists - never up through the drywall!).

Done!


- Stuart -

OK,I think I get it all now.

Many Thanks!