Originally posted by vitod
Again. Does it have the same isolation benefits as rubber? Remember. Rubber, Acoustiblok, has mass, lots of it. The more mass you can build, the better isolation. So, how can a glue have the same mass factor as rubber?
If your building walls with rubber and drywall, your talking major mass. If using GG, where's the mass?
Ok, let's talk about mass for a moment... A sheet of 5/8" drywall weighs 70-75lbs... or about 2.3 lbs/square foot
if we added a layer of roofing rubber that was 0.8 lbs/square foot to a wall with 2 layers of 5/8" drywall on both sides, we'd raise the mass from ~9.2 lbs/square foot to 10, or about <10%
by mass calculation, that would translate to 0.7 dB of added performance.
if we added rubber at 0.8 lbs/square foot to a wall with just 1 layer of 5/8" drywall on both sides, we'd anticipate 1.4 dB of improvement.
if we used heavier, 1lb/square foot material, the impact on performance due to mass would be 0.9 dB and 1.75 dB due to mass for the two cases respectively.
so, the added mass of rubber simply isn't/can't be a considerable factor in performance.
looking at cost... let's say that our 1lb/square foot rubber cost 2 bucks a square foot. that's 2 bucks a pound. Drywall costs maybe 8-10 cents/lb.
so if you want more mass, add more drywall, seems alot cheaper.
anyway, to the question at hand: if adding a rubbery product to a wall has a transformative effect on sound-stopping performance, it's not due to it's mass, the mass is trivial.
it would be due to damping or some type of isolation effect (like rubber pucks, perhaps), or changing in the resonant behavior (moving it to a lower frequency to get higher STC). it's not the mass. you have to add ALOT of mass to really change walls. Now, drywall is stiff and very resonant and transfers energy very well, so perhaps roofing rubber attacks the resonance (damping) or the transfer (some isolation effect)
Green Glue sure isn't a mass-loading material, it's a damping material.
Roofing rubber isn't a practical or meaningful mass loading material, either, so it's effect has to be something else.