I am ripping up tiles on the ground floor of my home and would like to install 1/2 inch engineered hardwood. It is over a concrete slab on grade. What is the best and most economical way to do this once the tiles are removed and the concrete is cleaned and leveled?
-Can I float a plywood subfloor and then nail the hardwood to it? If so should I leave expansion gaps between the plywood and the walls? I have seen this suggested on other forums but doesn't seems to make sense to me. Shouldn't the subfloor be screwed down if the flooring is to be nailed to it?
-Or should I secure the subfloor to the concrete and then nail the wood flooring to that? What is the best way to go about doing this?
-A modular subfloor like Dricore seems great but expensive and maybe overkill for an on grade floor?
What is the best recommendation for this type of project? What subfloor should I use, how should it be installed, where should the vapor barrier be placed and what is the best way to secure the engineered hardwood flooring to the subfloor?
Best Answer
If you're not wedded to a nail-down install, the best route to go with here is a floating floor with nothing but a soft underlayment between the flooring and the slab. This is an accepted install method for engineered hardwood over a slab, and your flooring manufacturer/seller should be able to provide you with instructions for how to do it and not void the warranty.
As for vapor barriers, you only need to worry about that if your concrete slab doesn't already have a vapor barrier underneath it. Obviously there's no way to easily check, but if the slab was poured in the last 20 or 25 years, there's a very good chance it already has one. In any event, once the current flooring is off, you should have a calcium chloride moisture test performed on the slab. Where you live matters, too. I live in the desert, so soil moisture is a non-issue here, and my slab's lack of a vapor barrier underneath it is irrelevant. If you're in the pacific northwest, it's a different story.
If the moisture test shows that you need a vapor barrier, choose a closed-cell foam underlayment, not something water-sensitive like cork.