Use a minimum of two layers 3 8 10 mm cd exposure 1 plywood subfloor panels cdx in 4 x 8 sheets.
Engineered wood flooring on plywood over concrete slab.
Alternatively screw rows of treated 1x4s to the concrete 16 in.
Lay 6 mil polyethylene sheeting over the concrete to minimize moisture migration from the concrete up into the wood flooring.
This may be as simple as a 6 mil polyethylene plastic covering 100 percent of the concrete and brought up all walls then trimmed after the floor has been installed.
Treated plywood to the concrete with concrete screws spaced every 16 in.
Install a subfloor solution.
Plywood on slab begin by covering the slab with a vapor retarder.
These layers enable the wood to remain rigid and resist contracting and expanding when moisture is present.
In general use a notched trowel to spread the adhesive.
Each engineered board consists of thin strips of durable wood compressed onto high grade plywood.
A subfloor is necessary to install before the flooring can be put into place.
Pass the trowel through the glue at a 45 degree angle and install hardwood flooring immediately after the adhesive is spread.
For a nailed down subfloor over concrete nwfa installation guidelines call for a minimum of 4 by 8 foot sheets of 5 8 inch cdx grade plywood or preferably 4 by 8 foot sheets of 3 4 inch cdx grade plywood.
Installing engineered hardwood flooring over concrete too tight against a stationary object will not allow room for normal expansion and may cause a failure.
Plank flooring four inches and wider requires either the plywood on slab system or the sleeper system topped with a minimum of 5 8 inch thick plywood or osb.
Consult the product data sheet for instructions regarding specific trowel requirements.
The nwfa guidelines say that a vapor retarder over concrete needs to be impermeable meaning a class i membrane according to building codes.
A plywood core makes engineered flooring the most stable choice provided the slab is flat and dry by ken fischer issue 170 if you want to install flooring on a concrete slab your floor covering choices are limited.