Hi All, We're currently having a new floor installed in our apartment in NYC. We live in a high rise building and therefore have a concrete floor. The contractor removed the old parquet floor and vapor barrier. A tar like material remained. Removed granite tiles in the kitchen. Then he installed 3/4" plywood over the area where the previous floor was and kitchen area. The plywood was installed with glue and nails. The subfloor has been down for about two weeks. After walking on it I'm starting to hear pops. The maple has yet to be installed. Questions are: 1) should a vapor barrier be under the plywood? Should the kitchen area had a layer of self leveling cement applied? 3) Should the subfloor be secured to the concrete using TapCons. 4)What is causing the pops in the subfloor? This site is great.

Yes, Yes, Yes, & Yes.

There should be a vapor barrier under the plywood, usually 3 mil plastic is used for this.

It depends how uneven the kitchen was after the tile tear out, if it was flat but with some gouges from the chippin hammer then a self leveler would not be needed, however if it was all up and down with chunks of thin set left then maybe yes, the thin set needs to all be removed.

There are some good pneumatic nailers made for the sole purpose of attaching plywood to concrete, they use 1 1/2" - 1 3/4" hardened steel nails driven under huge air pressure.

Hand nailing could be the reason your hearing pops. Fluted masonary nails wont bite very well if pounded in by hand to a slab that is either too hard or too soft, the impact of driving the nails in can weaken the hole and cause the nail too come loose in time.

Also check with the building by laws to see if they have IIC rules. Many condos and apartments have strict rules for sound transmission so the person in the unit under you wont hear a pin drop in YOUR apartment. Maple nailed down onto semi loose plywood will sound like a drum over your head to the person underneath you. You need to have some kind of sound supressing underlayment, cork etc'