Before installing your beautiful new flooring, the most important step is to consider how much moisture is in your concrete slab. This measurement is referred to as the moisture vapor emission rate (MVER). The next step is to find out the moisture sensitivity of the floor covering and the installation materials. If you don’t know, step back for a moment and find answers to these questions. Many decorative floor coverings and their installation materials are sensitive to excessive moisture, causing them to swell or blister, and wood flooring may even buckle. The adhesives used to secure the flooring to the concrete substrate may also be sensitive and dissolve under the floor covering. Continued exposure to moisture allows mold to grow under the flooring material, which can cause discoloration of the flooring and affect the health of the building occupants.
Persistent moisture typically comes from the concrete substrate in the form of vapor. Moisture vapor is the gaseous form of water. It surrounds us every day and is measured as relative humidity in the atmosphere. It is also found in any concrete slab. Water is added to the dry concrete mix to improve mixing, pouring and placement of the concrete. Part of the mixed water will bind to the cement particles in the concrete through a chemical process called hydration. The excess water not needed for hydration must leave the concrete as vapor. This is a slow process and can take as much as one month for every inch of thickness in the concrete substrate. Concrete has a crystalline structure with many capillaries between the cement crystals and aggregate content. These capillaries allow the movement of moisture vapor through the concrete. Based on the laws of physics, the moisture vapor will move to areas of lower concentration or lower relative humidity. The moisture vapor will move to the surface of the concrete through the capillaries where it can accumulate and affect moisture-sensitive floor coverings and installation materials. This occurs in suspended concrete slabs as well as in concrete on ground.