February 2012

Hardwood Floors Over Concrete

If you love solid wood floors and your home rests on a concrete slab, you're not out of luck. But it's considerably more difficult to install 3/4 inch wood floor over concrete than over a wood subfloor.

The biggest problem with this type of installation is moisture coming up through the concrete which will damage the wood flooring. Be absolutely sure that the concrete doesn't get damp because of exterior water problems. You can test for moisture evaporation in the concrete slab by taping a 16-inch square of clear 6-mil polyethylene film to the slab. Seal the 4 sides with moisture-resistant tape so the moisture cannot escape. Do this in several different areas around the room. (Sometimes moisture may be more concentrated in one area of a room than in other areas.) If no condensation collects under the film after 24-48 hours, the slab should be dry enough for floor installation. You do not want to glue this type of flooring directly to the concrete. If you do, you will be asking for problems in the future. They are laminates that can be glued directly to concrete.


First, lay a plastic moisture barrier over the concrete to prevent any moisture from soaking into the wood. Lap all seams by 6 inches. You can purchase moisture barriers from any building material supply company or home center. Make sure it is a minimum of 6 mils thick.

Next, you need to provide a nailing surface for the wood flooring. Some people try to get by with furring strips anchored to the floor. This is the old way of installing flooring and is no longer the preferred method. We recommend installing 3/4” 4x8 sheets of pressure treated plywood. The pressure treatment is another safe guard to prevent moisture from reaching the wood floor. Screw or power nail the plywood to the concrete. You can rent concrete nail guns from home centers or tool rental companies.


Make sure the nails penetrate the concrete by a minimum of  3/4 inch.
The next step is optional. Not all pros agree with it. I recommend laying down a layer of 15 pound roofing felt. The felt eliminates the possibility of the oak flooring rubbing against the plywood which could create squeaks. It is an easy step to do now and impossible to do later.


Your hardwood flooring must adjust to the “climate” of a room before it’s installed. Don’t have it delivered on a wet day. Make sure all humidity producing aspects of building and remodeling have dried before bringing the wood home. Acclimate the wood to proper room temperatures for five days prior to installation, at temperatures of 65 to 75° F. You can stack it log-cabin style or just spread it around the room, but not directly on concrete. It is a good idea to either rent or buy a moisture meter to check the moisture of the subfloor and the oak floor. Moisture content of both should not exceed 12%.
You are finally ready to start laying the strip flooring. You will want to provide a 3/4 inch space on all sides of the floor to allow for movement. The floor will expand in the summer and contract in the winter. Be sure to butt the boards tightly together. You do not want any space between them.


Begin by selecting a long board to start the first row. Pick one that is straight. Align the edge of the board with the chalk line and drill pilot holes down through the hardwood plank and into the plywood. Face-nail the first boards at the point of every joist and set the nail with a nail-set. Remember to keep the board lengths random. It is important to face-nail the first row because the pneumatic nail gun will hit board and the force would push the wood against the wall, and loose the 3/4" expansion space.
Lay out a box of hardwood boards ahead of the installation to visualize lengths, wood grain and colors of the boards. When laying out the boards, keep in mind to never have the ends of boards in adjacent rows line up with each other. Keep the lengths random and at least 6" in length.


Using the pneumatic nail gun, place the gun lip over the edge of the board and strike firmly with the mallet, driving the staple into the tongue of the hardwood plank.

When you have completed the installation process, the final stage is sanding and finishing. I know many do-it-yourselfers will want to try and sand the floor. This step is the most difficult to do correctly. I see many floors that are not smooth which is a sign of amateur workmanship. It is highly recommended to have a professional come in and sand the floor. You should be able to stain and finish it by yourself.


Hardwood floors will give you a lifetime of enjoyment.

Quote Of The Month

The most important things in life….aren’t things.

A Tip Of The Hat To:

Robin Lanese
Atlanta Housing Source, LLC
20 Lenox Pointe
Atlanta, Georgia 30324

****Thank You**** 

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