We bought 5/16 " x 3 Engineered wood. We are installing it on below grade floor... putting 3/4 inch plywood on concrete.... we've already started. We were told by the HD guy in flooring that the polyethelene film for moisture barrier goes between the plywood and the floor(hardwood floor)
My fiance is considering ripping up the plywood he has already put down for these reasons/potential problems:

1. polyethelyne film not between concrete and plywood (some vinyl floor tiling is tho).
2. he used powder actuated tool to nail plywood down but was nailing corners first(now we know center should be nailed first) some corners popped up despite nailing.
3. where one plywood piece is up against the other he has approx 1/4 or slightly more space. we think thats too much??
We NEED HELP or reassurance or encouragement or reprimand!! whatever just someone please tell us what we should do and still be able to staple the flooring down properly.

hmmmmm,,, did I ask dumb questions??
would someone tell me something to help us with this project.
any opinions are welcome. Please.

Well, I just got home, took my boots off, made a pot of coffee, and turned the news on the TV, clicked the puter on, and surfed the installer boards first before I got here. I hope I didn't make you wait to long, But it sounds like you have it already figured out.


First you flatten the substrate to the strict rquirements of 3/16 of an inch, in 10 feet, or for smaller areas, 1/8 of an inch, in 6 feet. Use a 8 to 10 foot straight edge on the concrete to varify the flatness and correct (grind, & fill) where it needs it.

Then You need asphalt mastic. Then 15 or 30# asphalt impregnated felt. Then a plastic barrier, sealed at the seams. The asphalt mastic, seals the fastener penetration(32, per 4x8 sheet/panel)

You can now fasten down the panels. Start in the corner next to the existing panel, and fan out your fasteners. The first panel you can start in the middle, and like tightening a head gasket on a car, work to the outside, but all the panels after that, from a corner and fan across the panel.

Leave a little gap between panels.

Oh ya, I hope your using tongue & groove plywood!!! Or your installing it on a 45º!! Or your installing the flooring on a 45º to the plywood. You don't want a long seam falling with the flooring rows.

I will say this. Lots of ways to lay plywood over concrete. Glue, screw, nail, float and various ways and systems. Some work, some don't. No one system is PERFECT in every situation. IMO, it takes a pro to know which system has the greatest chance of success in any given location. If you are below grade, you are best off sealing the slab with a moisture proofer, laying 8 to 10 mil poly and floating an engineered over that. That's the best way to isolate the flooring from moisture the slab will emit.