Have you ever heard a flooring Installer or Service Technician refer to a high moisture reading and wondered what he was talking about?

Determining moisture content is an important part of quality control during the installation process. Flooring professionals use a moisture meter to determine how much water is inside the cells of the sub floor and the boards which make up the hardwood floor.

Normal Readings

A normal reading is between 6-8% for the individual boards; the average will be lower in winter and higher during the humid months of summer. Readings above 12% in winter and 14% in summer for the sub floor are considered unacceptable.

These are not arbitrary numbers. The National Wood Flooring Association and various wood flooring manufacturers have done extensive testing to determine what the effects of moisture on hardwood flooring are. They have determined that a variation of over 4% between the level of the sub floor and floorboards at the time of installation will result in cupping, crowning, gapping, and excessive movement in the flooring as the moisture travels from the sub floor into the floorboards and then out into the atmosphere again. In other words, the floor is ruined and in need of serious repair or replacement.

Where does moisture come from?

The term “ambient moisture” is often used when referring to humidity or the amount of water in the air.

In the summer months, when the air is warm and can hold more moisture, evaporation causes moisture to be transferred to the atmosphere leaving us with hot, humid days. This moisture often enters a house through open doors and windows during the day, and then the house is usually shut down at night. The house is allowed to cool down naturally overnight or exposed to an HVAC system. As the air cools, it is no longer able to hold moisture. This moisture is absorbed into all permeable surfaces, or in the case of impermeable surfaces, it becomes a light dewy coating.

This is the most common cause of high moisture readings, but other environmental factors can influence the readings as well.

If the house is sitting next to a body of water, is improperly sealed, or has been subject to leaks or pressure washing, the reading will often be above recommended limits.

Prevention and Cure

The main cure for this problem is time, and that is usually in short supply on a job site. Closing up the house and running the HVAC system may be enough to lower the ambient moisture in a house.

The next step would be to run dehumidifiers and/or fans to remove the water from the air. This process could take anywhere from days to weeks depending on the cause of the moisture and the ability to keep the home sealed.

Prevention can keep a house on schedule and minimize costly repairs and delays. We recommend properly sealing the house (windows, doors, weather stripping, and plumbing fixtures are intact before hardwood installation), keeping the home closed with the HVAC system running just prior to and after installation, and minimizing activities which release large amounts of moisture into the air (such as pressure washing) just prior to and after installation.

If you have any questions about moisture related damage or would like to schedule flooring pre-inspection, please contact Mike Bailey in the Custom Hardwood Department.