Wood Floor Cupping & Other Common Problems: Spotting the Trouble

Installing hardwood flooring is hard, thoughtful work that, if done properly, can yield lifetimes of warmth, elegance, and beauty in a home or commercial setting. As you eagerly anticipate a successful installation, be aware that problems such as warping, buckling, cupping, and crowning can really ruin your floor and your dream. Fortunately, there is a way to mitigate the risk of these depressing conditions. A little bit of knowledge and one good tool can help you. Read on and let’s get started.

wood floor cupping failure

First, many homeowners and even pro flooring installers may not realize they need to measure the moisture content (MC) before, during, and yes, even after installation. In fact, commercial property owners and homeowners should never stop monitoring the MC of their hardwood flooring if they wish to keep it pristine, beautiful, and flat. Here’s why…

Wood Expands or Contracts According to the Season

This happens because wood loses or gains moisture depending on the relative humidity (RH) and temperature of the surrounding environment.

Here’s how it works…

Wood Shrinks as Its Losing MC

When you turn up the heat in the winter, the RH level inside your home decreases. This causes hardwood flooring boards to lose MC and shrink. In fact, you might even see spaces appear between boards during the winter.

Wood Expands as Its Absorbing MC

When you turn off your heat in the spring and open the windows your hardwood flooring boards will begin to expand again. The spaces between the boards that were there during the winter will probably now disappear.

So, the expansion and contraction of hardwood flooring are normal. It’s just something that happens as the seasons and RH change. You should expect to see gaps form between wood flooring boards during the winter. However, those gaps will probably close naturally during the spring.

Use a Moisture Meter to Monitor Your Wood Flooring

All owners of wood floors should invest in a high-quality wood moisture meter. Moisture meters measure the MC in wood and when it comes to professionally installing wood flooring material, they’re a valuable tool of the trade.

No qualified and experienced contractor would ever install a wood floor without a moisture meter. This is because prior to any installation, the wood must reach its ‘equilibrium moisture content’ or EMC. This is a point of balance between the MC of the wood and the RH of its ambient environment. If the wood isn’t allowed to reach its EMC prior to installation, problems could develop later.

Wood flooring owners should continue to monitor the MC of their wood flooring after the installation as well in order to avoid any moisture-related problems.

The following list of problems isn’t exhaustive. However, it does cover some of the more common ways moisture changes can negatively affect wood flooring.

Whether you’re an installer or a homeowner, knowing what causes wood floors to fail is the first step towards preventing failures.

What causes wood floors to cup

What Causes Wood Floors to Cup?

Cupping in hardwood floors is caused by changes in moisture levels, whether decreases in the air RH above or increases in moisture from below. Other causes of hardwood floor cupping could include situations such as basement plumbing leaks that allow moisture to migrate up into the subfloor and into the wood flooring or the heat from a wood stove that drys out the air in the environment.

hardwood flooring moisture problems

Watch our hardwood floor problems – common causes video series.

Whatever the cause, a moisture imbalance develops from the bottom of the floor to the top. This imbalance causes each plank to develop a concave shape with pronounced raised edges.

When you see cupping, you need to identify the moisture source. Is it due to low indoor RH or a plumbing leak? Once you’ve identified and controlled the moisture problem, you might be able to reverse the cupping.

Minor cupping is a natural reaction to moisture and shouldn’t be a concern. However, severe cupping indicates a serious moisture imbalance.

As the saying goes, an ounce of prevention is worth a pound of cure and this definitely applies to wood flooring. Everyone who owns a wood floor should use a moisture meter on a regular basis to identify moisture changes that can lead to cupping.

What causes wood floors to crown

What Causes Wood Floors to Crown?

Wood floor crowning is the opposite of cupping and happens when the center of the board is higher than the edges. Like cupping, wood floor crowning happens because the boards are exposed to a moisture imbalance over an extended period of time.

Crowning can also be caused by previous floor cupping. Here’s how that happens…

A cupped floor needs ample time to dry. If the floor is sanded while the boards are still cupped, the sanding process will sand off only the raised edges of the boards. When the floor dries and returns to a normal MC, these sanded edges will be lower than the center of the boards.

What Causes Wood Floors to Buckle?

Buckling of hardwood floors occurs when the wood actually pulls away from its subfloor lifting up to several inches in one or more places. Buckling is an extreme reaction to moisture and fortunately, doesn’t happen very often.

Buckling is often due to flooding and happens after hardwood flooring has been submerged for some time. However, buckling can also be caused by insufficient nailing, incorrect nails, incorrect construction of concrete subfloors, or failing to use a vapor barrier (also referred to as a moisture barrier) or vapor retarder. With glued floors, buckling can be caused by incorrect mastics, inadequate mastic transfer, subfloor separation, or subfloor contamination.

Fortunately, even buckled wood floors can sometimes be repaired instead of totally replaced.

Any moisture imbalance can cause problems with wood. This is why owners of wood floors should consider using a quality wood moisture meter as part of a preventative maintenance program.


Free Download – 4 Reasons Your Hardwood Flooring Failed

Other Common Problems with Wood Floors

Spaces Between Boards

We touched on this above. When it comes to wood, almost every type of flooring endures some expansion and contraction as seasons and humidity levels change. For example, when homes are heated during the winter, humidity levels drop, boards shrink and spaces appear between them. During any dry season, cracks can easily develop to the thickness of a dime on a typical solid 2 1/4″ oak floor. Light-colored woods will make these cracks appear even larger.

These spaces are to be expected and usually close up when moisture returns to the air. However, can use a humidifier to add moisture to the air during a dry period.

How Do You Fix Cupped Floors?

If you see serious cupping, you’ll need to first identify the source of the moisture. Once you’ve taken care of it, the floor should dry out by itself over time. You can use fans to speed things up, if necessary. Remember, minor cupping is a perfectly normal reaction to a change of humidity in the environment.

Will Wood Floor Cupping Go Away?

It might. Minor cupping is not a problem and is something that you should even expect. When the temperature and humidity change, the cupping will probably go away.

Major cupping caused by water damage is another matter. However, it’s possible that once you’ve determined the source of the moisture, the floor will dry out eventually and the cupping will disappear. However, you may need to sand and refinish it though.

Will Cupped Floors Flatten?

Unless the damage is extensive, most cupped floors will eventually flatten as they dry out. As we’ve pointed out, minor cupping is normal and to be expected. It will go away as soon as the weather changes. However, even more serious cases of water damaged floors can sometimes be resolved by simply allowing the floor to dry out naturally.

Always Use a Moisture Meter

Whether it’s a building, a wood floor, or another type of wood product, if you want to maintain the value of your investment, you’ll need to spot moisture problems before they occur.

Wood moisture meters have come a long way since we formed Wagner Meters in 1965. Today we carry wood moisture products for lumber mills, building inspectors, installation contractors, wood hobbyists, and the owners of wood floors.

Yes, our moisture meters are designed for professional flooring installers and building inspectors. However, homeowners will find Wagner Meters’ quick scan capabilities useful for regular home maintenance.

Wagner Meters’ non-damaging pinless technology allows any user to easily, quickly, and accurately determine wood MC.

Last updated on August 31st, 2021