I have a question about vapour barriers over concrete:

I would like to glue down plywood to my radiant head concrete slab, and then nail down 3/8" solid white oak, quartersawn.

Should I glue the plywood, then apply the vapour barrier, then nail the wood OR

Should I glue the vapour barrier, then glue the plywood, then nail the wood.

Thanks !

You should flatten the concrete to 1/8" in 6'.

Then the moisture barrier. Then cut your 4x8 sheets of plywood, into 16" x 8 or 2x8 panels. Loose lay them in the opposite direction of the flooring, staggering the joints at least 2 feet. Maintain an expansion gap around the loose laid panels & the walls.

Now nail down your flooring, making sure your fasteners, do not blow through the plywood, and puncture the moisture barrier. 1½" fasteners for ¾" hardwood, over ¾" plywood.

I'm the over kill type when it comes to moisture barriers. I roll out asphalt impregnated felt paper over the plastic 6-mil or greater moisture barrier, over lapping the seams 4"

The problem I have with loose lay, is that it will essentially feel like a floating floor, which I don't want.

Why, exactly can I not glue the plywood down? Can't I also glue the vapour barrier down?

Julie

The vapor barrier has to go under the plywood. If you cover the plywood with a moisture barrier, sandwiching it between the concrete(moisture) and the moisture barrier, it is going to do a number on the plywood. Besides, poking thousands of holes in it from the flooring fasteners!

Where is your moisture barrier, if you glue plywood to the moisture laden concrete?

What happens to your mosture barrier if you poke holes all in it??

You will have $2 per foot in a moisture blocker sealer & Urethane adhesive system. Then $1 a foot for the ¾" plywood. $50 for a box of fasteners. Then what ever the flooring cost per foot.