Resilient Channel 2nd drywall layer

Hi guys, hoping someone could givee me some advice, Ive got 5/8 drywall hanging on resilient channels on the walls. i want to put another layer of 5/8 drywall over it. Is it better to screw drywall to the drywall with short screws, (1" or so so i dont hit the studs) glue the layer on, or try to screw it also to the RC ?. i thought i may have read somewher NOT to glue it if its on RC. I may be mistaken though. If I do glue, what glue is best other than green glue, i really dont have enough cash to spend at $12 a tube at 2 tubes per sheet. any comments will be appreciated. thanks, ds

I think the verdict is, screw it into the RC and be careful not to "short out" (i.e., don't screw into any studs). Whereabouts are you in Northern California? 8)

thanks. yeah, ill just have to mark em carefull. curious,why is gluing out? does that mess up the sound control of the rc. im up in the brentwood/antioch east bay area

Gluing causes the two sheets to be effectively joined as one, which affects resonance frequency in a negative way. FYI, you can use Green Glue at <100% of its recommended dosage, albeit with a decrease in performance. If you can afford to use one tube per 4x8 sheet, there should be a benefit. --Keith :mrgreen:

You should be able to use 1 5/8" fine thread screws for the 2nd layer.

ds wrote:

If I do glue, what glue is best other than green glue, i really dont have enough cash to spend at $12 a tube at 2 tubes per sheet. any comments will be appreciated. thanks, ds

Just to clarify something - Green Glue is not actually "glue", and you don't use it to make layers adhere to each other. Green Glue is a damping product to aid soundproofing, and where it's used, screws also need to be used, to actually fasten one layer to the other. If you're using glue INSTEAD of screws, you need an actual adhesive glue. The good news is that this will be many times cheaper than Green Glue! On the other hand, I second the opinion above that you're better off not gluing the layers, for acoustic reasons.

thanks for the advice guys...

Specifically, the coincidence frequency (weakest point) of a single layer (or several, if they are NOT glued) of 5/8" drywall is around 2500 hZ - for twice this thickness in ONE sheet, the coincidence frequency drops to about 1250 hZ. The lower the frequency, the harder it is for the wall to stop it - so lowering this frequency by a full octave will weaken the wall by about 6 dB. Using two NON-glued layers, the coincidence stays at 2500 while the mass doubles, compared to a single layer of 5/8 drywall... Steve

Thanks for clarifying, Steve... Sometimes I know the what not to do but I don't necessarily recall the precise why not to do it. ;-)