What makes hardwood floors cup

Floor finish slows water movement but does not stop moisture passage into or out of the flooring completely, so wet floors that have finish on them dry out slowly. As wood responds to environmental changes, the boards in a floor can experience forces from adjacent boards and from the subfloor. When increasing MC causes a board to expand, the rest of the floor pushes back and restricts the swelling to some extent. Wood has an elastic property in response to a force applied to it.

If a board is bent a small amount, it will go back to the original shape when the bending force is removed. Similarly, wood constrained from swelling in the range where the size would have changed less than one percent returns to the original size when the MC returns to the initial value. On the other hand, if the MC increases enough while the wood is not allowed to swell by adjacent boards, it acquires a set and will not go back to the initial size when brought back to the original MC.

This is called "compression set. If you hit a board with a hammer lightly, it bounces with no damage. A hard hit will cause a dent. In severe cases, floors that have been at an elevated MC may experience compression set and have permanent gaps between the boards.

Set can often be reversed by treating with steam, but this is not a viable solution for an installed floor. Following the theme of effects due to forces within a floor, there seems to be a phenomenon similar in appearance to the cupping due to a moisture gradient, but with a different cause.

A floor installed at too-low MC will swell as it reaches an equilibrium moisture content. Due to the taper of the side match from wider at the top to narrower at the bottom of the flooring, the boards experience more force across the face than across the bottom, and they become concave on the surface. A preliminary small-scale trial to reproduce this effect has been successful in generating a concave surface without introducing a moisture gradient that increases from the face to the back in the wood.

In many cases of slight to moderate cupping, eliminating the source of the water and drying out the flooring can save the floor. As noted previously, moisture movement within wood can be slow. Just running a fan or dehumidifier for a week will not solve most problems. As in a dry kiln, a combination of heat, air movement and low humidity is the most effective way to dry wood. Commercial drying services that utilize large external dehumidifiers or mats to draw air through the floor may be available.

With active measures, it can take a significant amount of time to dry a floor. Without active measures, it can take months. Sanding a cupped floor flat before it is brought to a normal MC can eventually result in a crowned floor convex surface once the drying process is complete. At this point, the floor may now be ruined and need to be replaced. Wet floors should not be sanded flat until the drying process is completed.

Unlike solid wood, some engineered flooring cups when the MC is lowered. Although all engineered flooring is not designed in the same way, a common construction involves the face of the desired species applied to a backer.

The backer often plywood provides structural integrity and stability in changing moisture conditions for the relatively thin face. The MC of the face and backer should be the same at the time of manufacture. The moisture level at the time of manufacture should also be the same as the MC the product will experience during use. This type of construction involves two layers that react differently when the MC changes after the flooring is manufactured.

Engineered flooring will perform best in the MC range near the value it had at the time of manufacture. Never use an overly wet mop or excessive water to clean your hardwood floor, and never use a steam cleaner. Instead, go over the flooring when needed with a dust mop. When you need to wash the floor, choose a hardwood floor cleaner with care because many will leave an ugly, sticky film. We recommend using our Gaylord Floor Cleaner which evaporates rather than settling on the floor.

Read our "Problems" article to understand, and prevent other hardwood flooring issues:. Close search. Factory Outlet Shop Our Floors expand. Have you ever stood on a hardwood floor and noticed that the boards appear wavy and washboard-like? Sometimes the early stages of cupping can be noticed when light comes in from a window and reflects onto a wood floor.

You can see small shadows where the edges of each floorboard are slightly higher than the middle. In short, moisture. It can still react with the moisture content MC in the air around it. Materials like wood will balance equilibrate its MC with its surroundings, similar to the principle of osmosis. So if the air is humid, the wood will absorb more moisture from the air and it will swell.

If the air is dry, wood fibers will release some of its moisture back into the air and it can shrink back down. This is why the bottom of the board swells and makes the edges curve upward into an almost wave-like pattern. Cupping can happen even to a flawlessly-installed wood floor, depending on the conditions of the building and the environment.

However, several common situations that are known to cause cupping can be addressed, and can even be reversed. Avoid cupping related moisture issues with an accurate wood moisture meter to test hardwood flooring. Buy an Orion Meter. Depending on the type of moisture issue, however, will determine how easily it can be fixed or how much effort it will take. Besides the visible warping of your hardwood floorboards, the floor could fail. The cupping could continue to worsen and create gaps between the boards.

The big issue, however, is still moisture. While cupping can remain after a severe event like flooding, persistent cupping is worth investigating. Prolonged moisture issues can lead to many types of flooring failures, so it pays to be safe.