I don't do wood floors for a business, although I have put in a number of them.
I would shoot down a plywood substrate if I was working over a cement screed. That would eliminate the hollow sound a floating substrate has.
Concrete Answers for Flooring Problems
Information needed to advise
Is this engineered wood or solid?
How is it going to be installed glued direct or nail down over 3/4' Plywood.
What species of wood is it? Oak, Maple etc.
How wide and how thick?
What do the mfg's instructions advise?
I know of no wood that will allow 90% RH so what makes this one different?
Yes I saw that 85% requirement which NWFA will subscribe to. Anyway the nwfa is the authorative source for most manufacturers BUT as it is constantly drilled into us the manufacturers requirements if more stringent must be followed in all instances. For example we were getting ready to install a 5 1/2" wide x 3/4" thick solid brazilian chestnut an extremely dense hardwood and lo and behold perusing their instructions instead of 6" to 8" and within 1" to 3" of each end, NWFA and most mfgs, they required 4" to 6" and 1" to 3" first time I have seen a nailing schedule that tight.
REGARDING THE MAPLE INCREASE IN RH SEE BELOW:
The MFMA has revised the acceptable level of relative humidity in a concrete slab for non-glue down floor systems from <=80% to <=85%. This revision was made in response to feedback received from our contractor members during the past several years. The MFMA Technical Committee reviewed this information and felt confident raising the level to 85% based on contractor experience with successful installation of maple systems over concrete slabs with relative humidity level in excess of 80%.
MFMA continues to only recognize the testing of a concrete slab’s relative humidity levels using the most recent version of ASTM F2170. Please refer to the instructions of the manufacturer’s relative humidity test kit for details on how to administer the test correctly. MFMA now recommends that the relative humidity level for a concrete slag for a non-glue-down maples floor system is 85% or lower and for glue down systems the relative humidity remains at 75% or lower before installation. For concrete relative humidity conditions above MFMA”s recommendation consult your MFMA Sport Floor Contractor or your MFMA Manufacturer.
So this means a sports floor over screeds not glued to the floor 85% is allowable BUT for glue down floors 80% is the requirement. Remember this is for sports floors. Manufacturers of Maple floors for other than sports floors the requirement by all mfg’s of residential is 75% relative humidity.
One must be careful about what exactly is the situation!