Hi. This is my first post but have been reading these forums for a little bit now. I'm planning on installing non-engineered hardwood flooring on my above grade concrete slab. This is in an apartment building so I would like to put cork down. Basically what I want to do is glue down the cork to the concrete and then glue down sleepers to the cork and then install the hardwood as usual. Will this work? Has this been done before or am I just making things up. Thank you for your help.
-Theo

I would suggest to use 2 layers of 1/2" CDX plywood instead of sleepers. And yes, it's a common system to use when you want some type of sound barrier for your flooring. That's the system we used at the local monestary and it's worked out great for them. We also ran a 1/2" bead of cork around all the walls and doors. Basically closed up the last 1/2" of the flooring with cork.

Thanks. I'm glad that I wasn't making it up. Now I have two more questions. What glue did you use for the cork and plywood and why did you use two layers of plywood instead of just one. Thanks for your help.
-Theo

We didn't glue. Lay out your cork or other sound reducing product. Floormuffler or some other acoustic reduction product will also work. Lay 1 layer of 1/2" playwood down the direction of your flooring. Lay second layer at a 45degree angle so when you install the flooring you won't have any sub-floor seam meeting a seam in the flooring. Then staple the two layers of plywood together using 1" staples. Ohh, and gap the plywood 1/8" to 1/4" to allow some movement.

Then nail/staple your flooring to that. The weight of the flooring and plywood will hold the flooring in place. About 4lbs per sq ft with flooring and subfloor. 6lbs with an exotic like Ipe or B. Cherry. 600 sq ft will be around 3,000 lbs.

Why 2 layers...the options are 1 layer of 3/4" plywood or (2) 1/2" for an industry accepted sub-floor to nail a hardwood flooring to. If you are gluing directly to the concrete 3/4" works well. With the cork between, you can glue the cork down, but will take a lot of time and not do much if anything. Gluing the plywood to the cork....would need to do some more research, but more then likely the glue bond and plywood movement will just tear it lose over time. Think it would best to just float it.

The 2 layers of 1/2" cdx is your standard gym floor sub-floor system, just adding in some acoustic reduction instead of thrust-a-cushions or other sports floor shock reduction.

Awesome. Thanks for the really detailed answer. That clears up everything. I feel confident now to start my project. Thank you very much for your help.