Wooden Floor on a Concrete Subfloor

Q: We decided to get wooden floor for downstairs and we found out that we have a concrete floor. So we will have to level it up. We live in an area where we feel the aftershocks of earthquake and our is already unleveled from it. So we know we are going to have it leveled up. I wanted to ask if it would be better to nail the wooden floor to the cement or glue it?
Thanks Navi
A: As a general rule in flooring, you can not nail a wooden floor to a concrete subfloor. The reasoning behind this is pretty simple: a nail down floor means you will be anchoring the floor without a moisture barrier. This means you guarantee yourself many issues with moisture causing warping and all sorts of other nasty problems in your brand new floor.
This being said, if the floor you have chosen is a 3/4” solid it is not recommended to be installed over a concrete subfloor. If this is an engineered floor or something like the 5/16” solids where they are approved to be installed over concrete by the manufacturer, then you will want to glue the floor down. With any glue down application, acclimation is key. Give your floor plenty of time to acclimate before installing, this could be upwards of a month if you are in a humid environment.
Any installer will mention you want your subfloor to be clean and flat – so you will need to level out your subfloor. Depending on how much damage your subfloor has taken from earthquake aftershocks, you may need to add fresh concrete. If your subfloor’s height differs by 1/2” or less you should be fine just using a self leveling compound. Before applying either of these solutions, ensure the concrete is clean and prepared in any way suggested by the self leveling or concrete’s manufacturer.