I am going to lay 6" wide pine t&g over a concrete slab. I live in Southern California a mile from the beach. What kind of prep need I do for the sub-floor? Can I lay plastic and then ply sub-floor right onto the slab and then nail or Hilti the ply down? Glue it too? If so, what kind of mastic do I use? How big an expansion joint is neccesary? Should I lay felt down on top of or beneath the plywood? I am doing two rooms and an entryway, about 1,000 sq ft total. I'm an old framer and I can hack thru the board installation, but the prep is a mystery but important part, I think. This is my first time installing a hardwood flr. Any suggestions will be helpful and greatly appreciated.

 

Solid hardwood flooring tends not to be recommended for installation over concrete below grade due to changes in humidity, moisture, and temperature in the concrete. Thus, the invention of engineered wood products for that purpose. I have also read there tends to be a tendency toward cupping of boards that are wider than 5". I have however seen in DIY books where folks install hardwood over concrete above grade. The slab must be level and with a trowel finish and cleaned to remove grease, oil, stains, dust. I have seen recommendations for 3/4" plywood subfloor for flooring 4" & wider. (I have also read that there tends to be a greater tendency for cupping in boards greater than 5".) Moisture/vapor barrier of asphalt felt and mastic or polyethylene are required. Flooring should be stacked indoors in the area where it is going to be installed for at least a week so that it can acclimate to temperature & humidity conditions before installation. Do not install over damp concrete or concrete that is subject to moisture.
patricia@www.twelvepole.com