There are few wood flooring problems more upsetting than cupped floors. Almost all wood floors will experience some contraction and expansion as seasons change. Cupping of the wood floor can be a natural reaction to these seasonal moisture changes, if they occur to a minor extent. If the cupping is more severe, it could indicate a serious moisture related problem with the wood flooring.
Wood’s equilibrium moisture content (EMC) is influenced by the relative humidity (RH) and temperature of the surrounding air. Wood will lose or gain moisture until it is in balance with this surrounding environment. Higher RH usually causes the expansion of wood, because the wood absorbs the increased water moisture vapors from the air; lower RH usually causes wood to shrink as it releases the excessive water moisture vapors back into the air. Seasonal weather and relative humidity changes can also affect and reflect changes to the wood’s (EMC).
Cupped floors occur when wood curls up and the edges of the board are higher than its center. Moderate cupping can be detected from a standing position when light reflects off a cupped floor with a wavy or slightly washboard look, or it may be readily viewed by the naked eye in more extreme instances. In these cases, it can also be possibly felt underfoot.
Cupped floors can occur for the following reasons:
- Low indoor RH is usually the main reason if the wood flooring was installed correctly. Sometimes, wood flooring simply absorbs enough relative humidity (RH) from the air that the flooring expands, compression sets in as the boards are crushed together, deforming the boards at the edges. The indoor humidity of the building should be controlled in this situation
- A moisture imbalance can occur throughout the thickness of the wood. The wood flooring is wetter on the bottom of the board than on the top. The moisture imbalance can be proven by taking moisture meter readings on the wood flooring.
- Excessive water spilled on the floor from a dishwasher leak. The excessive water is absorbed into the wood causing the wood to swell, crushing the boards together, deforming them at the edges causing cupping. The cause of the moisture leak must be identified and eliminated in order to repair the floor.
- A plumbing leak can allow moisture to migrate up into the subfloor and then into the wood flooring causing cupping of the floor. Again the cause of the moisture problem must be identified and eliminated in order to repair the floor. Remember that the minor cupping can be due to the seasonal effects of MC changes in the wood floor and not necessarily on poor installation. It is also important to know that seasonal effects will always be present, because seasons bring RH changes to our environment. Some cupping occurs naturally, but excessive cupping curls floors in a way that can require remediation.
Avoiding cupping begins before the wood flooring installation, of course. First, by measuring the RH of a concrete subfloor or by measuring the MC of the plywood or OSB wood subfloor with appropriate moisture measurement equipment, you can eliminate the subfloor MC as the cupping’s culprit.
Contractors and consumers can pre-empt cupping by measuring and monitoring the MC in the subflooring materials and in the wood flooring previous to installation. A wood floor is good to go when it reaches it’s (EMC). Accurate moisture measurement in all of the pre-installation stages, will ensure that the wood flooring will give the best performance homeowners expect.
If the cupping occurs after a proper flooring installation, moisture measurement still provides a key to solving the problem. A moisture inspection can identify problems that may have occurred after installation – like a leaking pipe – and give clues to the best solution possible. Once the source of the moisture problem is controlled, cupping can usually be cured. That’s great for wood floors, and the people who love them.