Hello everyone,

I want to use some type of cork underlayment between my new 3/4 plywood subfloor and nail-down hardwood (oak) floors) and would be grateful for advice.

1. Is 6mm cork ok or should I go with something thinner? I'm worried about potential compression/squeaks.... yet I do want to minimize sound transmission from the downstairs kitchen.

2. Do I really need to use a vapor barrier for a third-floor bedroom? Speaking of which - what sort of a vapor barrier? Does it have to be thick or is it basically as thin as, say, a plastic shopping bag?

3. I seem to be getting contradictory info on the web as to whether the cork underlayment will need to be glued down to the subfloor. I don't really get it - it will be held in place with lots of nails/staples once the hardwood flooring is installed on top of it, so what's the point of glueing? Also - what do I glue it to .... to the plastic sheeting mentioned above???

Thanks!

Masha

More questions to add to the list above:

Everywhere I looked, I read that cork underlayments are supposed to be used with a vapor barrier. What I don't get is - why do I need a vapor barrier in an upstairs bedroom at all and what's the point of one in a nail-down installation where it will be punctured 100+ times?

Even if I do use a plastic sheet between the subfloor and the cork, will I still need to use felt paper on TOP of the cork (between the cork and the oak hard wood)? If so, what for? Is it good for the cork to be sandwiched between two layers of sheeting?

Thanks!

Sandwiched betweeen layers, or under two floating layers if you need long fasteners.
See depth charts. You could get away with a 18ga instead of 16ga. Thing is NOT to hit the cork underneath or the subfloor.

http://www.powernail.com/naildepth/nail ... 6gauge.htm

Thanks Stephen. So, basically, I guess you're implying that it makes no sense to worry about any of the issues I listed unless I'm willing to install yet another layer of plywood on top of the cork, right?
Masha

Thats my take on it. You can't, or well should not nail directly over top of cork underlayment unless the manufacturer says so. Besides the cork, other underlayments that may allow you to kinda makes no sense since the fastener that gets into the underlayment or subfloor will transmit sound. But for insulation purposes I guess it is OK.