By Charlie Nielsen
Many installers feel when they lay a wood floor over concrete they are rolling the dice with moisture issues and hoping they don’t eventually receive the dreaded customer call that there is a problem with the product. When that call does come, it usually results in a merry-go-round of finger pointing and inspections with everyone trying to avoid being caught with the replacement costs of a floor.
Understanding the characteristics of the products being used and the environment in which they are installed can go a long way in preventing unnecessary call-backs or, even worse, floor replacements.
Wood is a natural product composed of cells that expand and contract based on the availability of moisture. Solid wood products are more susceptible to moisture in the form of cupping, and the wider the product, the more this is likely to occur.
Engineered products, however, are more stable due to the laminated layers. The more plys, the more stable the product. As installers, it is important to recognize that excessive moisture is the enemy of a perfectly installed hardwood floor and it can come from several sources.
Finding the cure
The concrete slab: Surprisingly, it takes only a small amount of water to cause concrete to cure. The balance of the water is used to make the handling and finishing easier. This water is often trapped in the slab by the use of curing agents, typically applied by the contractor to increase slab strength by slowing the rate at which the water can leave it. It leaves in the form of vapor. Testing a slab for this is vital to understand how much moisture the wood will be exposed too.
A calcium chloride test will tell you how much moisture in the form of weight is being passed from the slab in a 1,000- square-foot area over a 24-hour period. A gallon of water weighs about eight pounds. If you tested and calculated this amount, it would be the equivalent of spreading one gallon of water over a 50 X 20-foot area every day. It’s easy to understand why wood floors react when exposed to these amounts of moisture.
Note: If you have tested the area, and know that you have a moisture problem, make sure you use a recommended moisture barrier approved by the adhesive manufacturer you are using.
Humidity: This is the amount of moisture content in the air and, depending on where you live in the country, this condition will affect you different ways.
The ideal humidity level is around 50%. Lack of humidity can result in wood shrinkage and customer complaints of gapping and cracking. Too much humidity will result in cupping. The edges of the wood will become higher than the center, as the wood takes on moisture and tries to return to its natural form—a round tree.
Acclimating wood for a minimum of 48 hours or longer will allow the product to stabilize to its new environment (wood will either expand or shrink), before it is bonded in place permanently. This is assuming the new space is a functional, controlled environment. Installing wood in a newly constructed home in high-humidity areas without functional climate control can lead to a greenhouse environment inside the home.
Moisture drawn into the air from new paint, drywall, wood framing or trim can easily be absorbed by a kiln-dried floor covering product with damaging consequences.
Charlie Nielsen is the technical services manager, W.F. Taylor Co. To contact him, call 951.360.6677.
