Can Cupping in Hardwood Floors Be Fixed?

The tell-tale rise of floorboard edges across a brand-new white oak floor is enough to send any homeowner into a panic.

What do I do? Can it be fixed?

What about all that money I just spent on the floor!

Cupping is a common problem in hardwood flooring. It occurs when the long edges of each board rise up, forming a shallow trough in the center of the board.

And while cupping, especially minor cupping, can often be repaired, there are some cases in which replacement is necessary, especially after significant damage.

In this article, we’ll help you figure out the cause of your wood floor cupping and whether you can repair it. We’ll cover:

• What causes cupping
• Does my floor need to be repaired or replaced?
• How to repair a cupped floor
• How to prevent cupping

What causes hardwood floor cupping?

A moisture imbalance—more moisture on the bottom of the board than the top—is the primary cause of cupping in both engineered wood flooring and solid wood flooring.

This moisture problem can come from a number of sources:

• Water damage from neglected leaks and spills. Water seeps between the floorboards, causing the sides of the boards to rise. This is especially common in floors with finish, as it takes longer for them to dry out.
• Shifts in humidity levels. Low humidity in the air causes the top of the flooring to dry out and cup. Cupping caused by humidity tends to be one of the less severe types of cupping and may exist because of changes in seasonal conditions, such as going from humid summers to dry winters.
• Subfloor moisture. This could be from a humid basement or crawlspace or water leaks in the subfloor. It could also be from a concrete subfloor that hasn’t had proper time to dry and is therefore still leaking moisture up into the flooring.
• Improper installation of the subfloor. This could be a number of things, but the common denominator is usually moisture issues. If the subfloor is too wet, moisture moves up into the flooring.
• Heat from a wood stove or another heat source. Exposure to high heat nearby could cause the tops of the boards to dry out much quicker than the bottoms.

The flooring installation itself could also be at fault. If the flooring didn’t have time to acclimate to the new environment before it was installed, it could have had higher moisture levels to begin with, which could cause major cupping as the tops of the boards dry out first.

Looking at your shiny wood floor all cupped, you’re probably busy analyzing it (and remembering how much you spent on it!).

Can it just be repaired or do you have to replace it with a whole new floor?

Does my floor need to be repaired or replaced?

The severity and extensiveness of the cupping determine whether or not you can simply repair your floor. Severe cupping may require a complete replacement of that section or the whole floor.

Finding the source of the cupping—and the moisture—is the first step in finding out.

If the moisture is simply a result of change in humidity, for example, then all that may be necessary is a light repair, or none at all. Cupping because of humidity generally resolves itself with seasonal changes.

But if the source is a wet concrete subfloor, the whole floor may have to be ripped up—even if the cupping isn’t bad—and the concrete slab be allowed to dry before new flooring comes on top. If you don’t have time to let the concrete dry, a moisture mitigation system may need to be installed over the concrete.

Sometimes, replacing the damaged sections of floor is enough. But in a situation with severe cupping, a professional replacement of the whole floor may be necessary.

If the floor has only sustained mild cupping, a simple repair is very possible. We’ll look at how to do that next.

How to repair a cupped floor

Before you do any repairing—anything at all—it’s imperative to find the source of the moisture. If the source is ongoing (i.e. moisture seeping up from a subfloor or a continuous plumbing leak), repairing the floor won’t do any good. Within a few months or weeks, the cupping will be back.

Once you’ve found and resolved the moisture problem, then you can think about repairing it.

Next, take readings with a moisture meter to determine how much moisture is in the flooring.

Andrew St. James, PhD, who works at Goodwin Heart Pine, suggests this for a moderately-cupped floor:

“In many cases of slight to moderate cupping, eliminating the source of the water and drying out the flooring can save the floor.”¹

How is this done? Follow these steps:

1. Use a big, external humidifier and an HVAC system to get the room back to the right humidity level. The controlled climate of the room will help reverse the cupping, although it could take a few weeks or even months. Large mats to pull air through the floor can also help.²
2. Once the floorboards have flattened out again, check for any loose floorboards or nails (or staples—whatever were used to secure the floorboards). Places that squeak may indicate loose floorboards or nails.³
3. If the floor was secured using adhesive, check for places the adhesive has failed. You may want to contact the manufacturer to know how to repair it from there.⁴
4. Fill any cracked floorboards with wood putty or wood filler.
5. Sand and refinish the floor once the flooring has fully equalized to the environment.⁵ Remember, never sand the floor while it’s still cupped. This will only reverse the nature of your problem. When the floor returns to normal, the sanded parts will be lower than the center, causing the opposite problem of crowning.

Keep in mind that the repair won’t be instantaneous. St. James points out that “with active measures, it can take a significant amount of time to dry a floor. Without active measures, it can take months.”⁶

It may look like nothing is working, but be patient: in time, it will dry.

Solving the problem with climate control may work, but if the floor cups again (and again and again), there’s a more serious issue going on.

The cost of a professional repair will vary by location, the amount of work needed, and so forth, but an average rough estimate is up to $8 a square foot.⁷ Depending on the extent of the cupping, homeowners may pay a hundred or a few hundred dollars, or they may pay over a thousand. Professionals should evaluate the extent of the damage and name a reasonable price based on it.

Though floor repair is important once cupping has occurred, the best thing you can do is prevent cupping from happening in the first place.

How to prevent cupping

Cupping can be prevented by:

• Making sure the subfloor has the right moisture levels. If the subfloor contains excess moisture, especially if that subfloor is concrete, it will silently leak moisture into the flooring, causing it to cup. Since the cause is below the flooring, it will require a removal of the entire floor to address the subfloor moisture. Check before the flooring is installed!

• Before you install the floor, give the boards plenty of time for acclimation. Stack them flat according to the manufacturer’s instructions in the room(s) they will be going in. Allow them to acclimate for at least two days with proper ventilation. Then use a wood moisture meter to check them against the EMC (equilibrium moisture content) of the house.

• During installation, maintain the proper expansion gap between the edges of the flooring and the walls, following the manufacturer’s recommendations. This will give the floor breathing room for natural expansion that occurs after installation.

• After installing the boards, keep the climate of the room controlled. Have a humidifier and dehumidifier that covers the entire building. And use air conditioning and heat to keep the room temperature consistent throughout the year. This can help prevent seasonal cupping.

• Clean up leaks and spills as soon as you find them. Neglect allows the water to seep into the floor and cause regional cupping. Make routine checks around appliances, watching for signs of a leak. Dishwashers, washing machines, and refrigerators are notorious for secreting hidden leaks until it’s too late.

St. James adds jokingly, “Be lucky!”⁸

Moisture control can be done to prevent cupped floors, but it’s easy to miss something with today’s complex building designs. Be sure to follow all the above steps to have the best chance at avoiding cupping.

Moisture management is key

A home or office with wood flooring has an elegant, pleasing aesthetic and can make a home more valuable.

Cupping has the potential to take that away, and must be prevented and fixed when it happens.

Thankfully, cupping can be eliminated and avoided with proper moisture testing and management. One of the best tools to do that is a moisture meter.

And if you’re experiencing other problems in your wood floor,

1. St. James, Andrew. “Wood Floor Cupping: Why Does it Happen & What Can You Do?” Wood Floor Business, March 25, 2014. (↑)
2. Ibid. (↑)
3. “Repairing Cupped Floorboards,” U.S. General Services Administration, August 13, 2017. (↑)
4. Ibid. (↑)
5. Ibid. (↑)
6. “Wood Floor Cupping: Why Does it Happen & What Can You Do?” (↑)
7. “How Much Does Hardwood Floor Repair Cost?” Home Advisor, October 31, 2022. (↑)
8. “Wood Floor Cupping: Why Does It Happen & What Can You Do?” (↑)