If your home has a concrete slab subfloor, there are a few things you should take into consideration before purchasing any hardwood floor. Engineered products are recommended over concrete as they are more stable than solid wood. Luckily the selection of styles and wood species is much broader than it was just a few years ago. However, the installation is a bit more complicated .
Flatness
No subfloor is perfectly level. But is your concrete slab flat? There is only one way to find out and that is to take a straight edge and lay it down on the slab. Look to see how much space is between the edge and the slab. Ridges and dips may telegraph through the wood floor giving an uneven appearance and possible hollow noises or flexing when walked upon.
Small dips and ridges may be compensated for with a moisture-barrier film that has some cushioning added. There are several types of barriers and they are used between the slab and the wood flooring in a floating type of installation ( see below). The barrier also helps to prevent moisture from damaging the floor as well as quiets the floor and makes it a bit softer on the feet and legs.
Large dips and ridges must be removed prior to a glue-down installation of a wood floor. Ridges can be ground away and dips can be filled to achieve flatness. Van Briggle Floors can use a scarfier to grind out the ridges and avoid hollow sounds or flexing of your new floor.
Moisture
All concrete slabs need to be tested for moisture before installing any hardwood flooring product. There are several types of tests used as well as moisture meters. These test tell an installer what the moisture reading is on that day for that area. It is important to know these test results to validate the warranties on many flooring products. If the results are out of the proper range, an alternate installation or product may be necessary. It may be necessary to seal the concrete slab prior to the installation. Every job is different and ALL wood installation over concrete slabs must meet the manufacturer's specifications or the warranty is invalid.
You must keep in mind that other conditions will influence the moisture coming from a concrete slab. Changing ground water levels, improperly installed sprinkler systems and plumbing leaks are just a few of the problems we've seen over the years.
Be sure to have a floor covering professional inspect your slab prior to installing any wood product.
Glue Down vs Floating Installation
Since a wood floor cannot be nailed to a concrete slab, the options are to float the floor over a concrete slab or glue the floor to the slab. The choice often depends on the product you select. Some products,such as engineered flooring and parquets, can be glued directly to a concrete slab with the recommended mastic or adhesive spread on with the proper sized trowel. Sealing the concrete slab is often recommended prior to installing a glued down floor. This can prevent mositure from ruining your new floor.
Floating installation means the wood boards are connected to each other (either by a click-together process or glued to each other) but not mechanically connected directly to the subfloor. A thin barrier (a plastic membrane with or without cushioning) is placed between the slab and the flooring product. The barrier not only protects against moister, it also reduces noise and is softer underfoot. Sealing the slab is not necessary when floating a floor. But not all products can be floated! Be sure to ask your salesperson which products can be floated.
It is always a good idea to check with a floor covering professional. It is especially important when dealing with a concrete slab to make sure all warranties are validated and you will be happy with your choice for years to come.
