Can Wood Floor Cupping Be Fixed?

You’ve had a beautiful hardwood floor installed in your home. But after a while, something doesn’t look right—or feel right. Maybe the floor seems “wavy” or even rippled. You may notice small, raised ridges along the edges of some of the planks in the floor.

What’s happening to your previously gorgeous flooring? And can it be stopped?

Cupping is one of the unfortunately common issues that can plague hardwood floors. It can happen to most types of wood, and it’s often the first observable sign your floor is being affected by moisture.

Since wood reacts to moisture so easily, floorboards can warp as they react to the change in their internal moisture content (MC) after the floor’s installation. But if you catch it early and can address the moisture issue, there is hope in getting your floor back to normal.

Here’s what you need to know.

What does cupping look like on a hardwood floor?

Moisture in hardwood floors can cause cupping which looks like the center of the board is lower than the edges

When moisture interacts with a hardwood floor, the side of the boards closest to the moisture expands. This expansion can be in the form of cupping (the center of the board is lower than the edges) or crowning (the center of the board is higher than the edges). Both situations, although different, are both due to a moisture imbalance in the boards caused by either the addition of moisture or the extraction of moisture from the floor.

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.

Why does cupping happen?

Cupping is caused by moisture content
In short, moisture. Wood, even when it’s treated and sealed, is still a porous, fibrous material. 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.

It’s most common for moisture to enter the floorboards from below, through the subfloor. 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.

What are the common causes of cupping in flooring?

  • Change in the amount of moisture in the air (relative humidity). If you live in an area with humid summers and dry winters, or even vice versa, your wood floor can react to the changing amount of humidity in the air. It expands during one season and contracts in the other.
    If cupping is happening in a relatively uniform manner throughout your house, and the degree of cupping is not drastic, this is likely the cause.
  • Subfloor moisture. If there is excess moisture in the concrete slab, crawl space, or basement below your wood floor, this can cause cupping. This is especially common with new construction if the floor is installed before any type of HVAC is running within your home. It can also happen later if your basement or crawl space harbors more humidity in general.
  • Leaks or spills. Cupping due to leakage will usually be confined to areas around sinks, dishwashers, etc. If a leak is slow or small, the cupping can occur gradually and you may not notice it until it has gotten worse. Sudden leaks or spills can cause cupping if they aren’t cleaned up quickly or thoroughly, or some moisture is left behind.
  • Improper care/cleaning. On a similar note, especially when cleaning up larger leaks and spills, cupping can come about if any moisture is left behind after cleanup. What’s more, unless proper cleaning techniques and supplies are used, further damage could result as well.
  • Improper installation. If a hardwood floor is installed before a subfloor is properly dried, or before the floorboards reach an equilibrium moisture content (EMC), such as before the inside of a building’s air is conditioned, there is a chance for cupping later on. As furniture and people begin to inhabit the area, it will bring about a new level of moisture and temperature to the air. You want to ensure that moisture levels between the subfloor and the finished floor have reached proper EMC for the long-term. And to make absolutely sure the moisture readings are optimal for beginning the installation, you want the most accurate moisture measurement tools possible.

If cupping is discovered in an already-installed hardwood floor, can it be fixed? Does it need to be replaced?

Cupping can be fixed on hardwood floors depending on the moisture levels

In many cases, if cupping isn’t severe, the issue can be fixed once the moisture issue is fixed. Since the process of cupping is the wood reacting to moisture, if the wood’s moisture level returns to the proper equilibrium, the cupping can resolve.

Depending on the type of moisture issue, however, will determine how easily it can be fixed or how much effort it will take.

How to fix (and prevent) cupping hardwood flooring:

  1. Make sure you have a reliable wood moisture meter so you know how much the wood moisture content has risen or can identify wet problem areas. While several types of meters are available, few allow for multiple tests in multiple areas over and over without damaging the wood. The Wagner Meters Orion® moisture meter line uses electromagnetic wave frequency (EMF) to measure large areas.
  2. Determine where the moisture is coming from. As referenced above, is the cupping uniform and seasonal? Is it confined to one area? Has the floor been installed recently, or could there be more moisture in your crawlspace or basement than in the living space?
  3. Get a dehumidifier, especially if you have a basement or an area of the house that tends to be more humid than other areas. If you live in a place with humid summers, you may just need to run it seasonally to keep your wood floors in top shape year-round. The key is controlling the climate in your home, keeping it as consistent as possible.
  4. Maintain your floor properly, using the right cleaning methods and products made specifically for wood floors. Always dry spills thoroughly, and routinely check wood floor areas around sinks, dishwashers, bathtubs, and other areas more likely to have leaks or spills.
  5. After a significant leak or spill, especially if water or other liquids have had time to absorb into the floor and subfloor, you may need to contact the professionals for high-powered drying equipment. A dehumidifier is great for humidity in the air, but wet wood floors need a more direct and aggressive approach to avoid lasting damage.

What happens if cupping doesn’t get fixed?

Besides the visible warping of your hardwood floorboards, the floor could fail. The cupping could continue to worsen and create gaps between the boards. If/when the relative humidity drops, the boards may not go back to their original shape and can buckle away from the subfloor, or even splinter and crack.

The big issue, however, is still moisture. If the cupping in the floorboards doesn’t go away, it could mean that the underlying moisture issue was not properly addressed and still needs some attention. 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.

What NOT to do when you notice cupping in your floor.

One rookie mistake is to simply sand the floor down until it’s level again. But once again, the moisture problem that caused the cupping has not been dealt with. For example, if the cupping happened due to humidity from an especially wet summer and you sanded down the cupped areas, when the air dries out the wood can warp the other way, causing crowning.

You also don’t want to assume your floor has already failed. There is still hope! Many moisture issues can be fixed through household climate control, taking moisture readings throughout the house, or seeking out undetected leaks or spots where moisture could creep in from other areas.

To avoid these mistakes, there is a way to test for a change in your home’s ambient conditions over time. Relative humidity data loggers can tell you what has changed in ambient moisture levels when it changed and for how long. This information can help you determine what actions to take with your flooring.

The FIRST thing to do when cupping is discovered.

If nothing else, the appearance of cupping tips you off that your hardwood floor is susceptible to moisture problems. Even before you call a professional, if you have a reliable wood moisture meter you can use to take multiple readings throughout your home, you’ll have a much better idea of what kind of situation you have on your hands.

You might be able to figure out how to remedy the situation yourself if you find it’s due to humidity in the air or a leak or spill. And if you do discover it’s a serious issue, you’ll have much more precise information to give the professionals so they don’t have to spend as much time (and your money) doing detective work.

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Safeguard your beautiful hardwood floors with moisture measurement you can trust. Learn more about how Wagner Meters’ Orion® moisture meter line is easy to use while providing the most accurate readings available on the market.

9 Comments

  1. John Karam says:

    Hello Jason,

    My hardwood floors are newly installed in the upstairs throughout. Downstairs half of the floor was hardwood and the other half carpeted so we converted It all to hardwood. 3 months after the installation and cupping is occurring to all new hardwood floors. It is not existing in the old hardwood that was already there downstairs. I spent over $17K on my flooring and now I have cupping to all new hardwood. What can be done?! Thanks!
    JK

    • Jason Spangler says:

      John:

      Thanks for the question and sorry for the issues with your new floor. I guess the first thing to do would be to get the installer involved to give you an explanation and a course of action to remedy the situation. If that remedy doesn’t meet your expectations, I would look for a certified wood flooring inspector at http://www.nwfa.org and have them evaluate the situation.

  2. Sue says:

    Hi I have solid pine 22 yr old floor. I had a sink overflow and water went about 10×10 feet area. It prob sat for 15mins. I then got rid of water and ran 2 dehumidifiers and have wood stove on for 4 days. The floor is going back down but isn’t 100% flat yet. It is winter and when I leave in 3 days there’s will be no heat as it’s a seasonal cottage and we drain it and turn heat off. Will the floor continue to dry or will the cold temps make it worse. Thx for any info. Sue

  3. Molly says:

    I have a newly installed engineered oak wood floor throughout the first floor of our new construction home. The ends of the planks are lifting-edge lift? The floor was installed about a month before the HVAC was installed or running. The peaks are 1/8″ or under in certain areas. The floor inspector came today and read about 10% on the veneer (3mm) part of the floor and 18&20% on the 2 subfloor tests. My question is if it is possible for the floors to eventually flatten out? Is it possible for the subfloor to dry out? There are 2 coats of polyurethane on the floors.

    • Jason Spangler says:

      Molly,

      Thank you for the questions. Is this an engineered, sanded and finished floor on wood subfloor, or concrete? I will assume Engineered sand and finish floor. What’s happening with your floor is called “Endlift/Ski.” It’s a condition where the ends of installed engineered wood flooring boards deviate from the flat plane and appear raised or curved upward. There are several reasons this happens:

      • Flooring incompatible with the environment in which it is installed.
      • Engineered flooring that has experienced an increase in moisture, where the core material running perpendicular to the face of the board swells at a different rate and in a different direction than the adjoining layers, forcing the ends of the material to lift, which can then telegraph to the surface of the plank.
      • Inadequate or inoperable HVAC systems resulting in elevated humidity levels. (See Greenhouse Effect.)
      • Improperly selected, improperly installed, or improperly applied moisture control systems (vapor retarders) that do not provide adequate protection from below the floor.

      (Again, assuming Wood Subfloor and crawl space)

      The most critical aspect of this installation is for the moisture content (MC) to reach an equilibrium with the wood flooring, humidity, and subfloor MC. This is also known as the “Greenhouse Effect.”

      Once the subfloor, wood flooring, and humidity levels all equalize, then you can repair the floor by replacing them, or re-sand and finish the affected planks. It’s very likely they will not return to normal.

      It’s very important to make sure no repairs are done until the EMC (Equilibrium Moisture Content) has stabilized. The moisture content of the subfloor is very high based on your information. I would definitely find out what’s causing that. If its “green” wood subfloor and there is no cause for the moisture at your residence, the subfloor should dry out as long as you have proper ventilation under the home. I would make sure there are no leaks under the house. Also, make sure that there is black plastic covering the crawl space.

      Hope this helps.

  4. Tom Kinnear says:

    Hey Jason, we live in NW Florida and had engineered hardwood install three years ago over a cement slab in our great room. Within a year after the installation about a half dozen planks have cupped. The installer said it was moisture under the slab and eventually every plank would start to cup. The installer suggested we have the flooring removed, place a moisture barrier over the slab and have a new floor installed. Seriously!
    Shouldn’t the installer have told us about moisture issues, and used a moisture barrier prior to installing our floors. I’m contemplating legal action. What are your thoughts? Thanks, Tom

    • Jason Wright says:

      Tom,

      Thanks for reaching out. We understand your frustration. I have added some information from NWFA that should help out. National Wood Flooring Association (www.NWFA.org) is the standard for which ALL installations of hardwood flooring must follow. Please see below the information from NWFA. I hope this information is helpful, best of luck!

      Engineered Wood Flooring

      A. Prior to delivery of the wood flooring, check and record the jobsite ambient conditions and the subfloor moisture to ensure they coincide with the wood flooring requirements that have been selected.

      B. Upon delivery of the flooring to the jobsite, recheck and record the temperature and relative humidity in the space receiving the wood floor. The temperature and humidity must be within the manufacturer’s requirements.

      C. Upon delivery of the flooring to the jobsite, recheck and record the MC of the subfloor. Check with your moisture meter manufacturer to determine the correct setting on your meter for the wood subfloor being tested. 1. Take MC readings of the wood subflooring at a minimum of 20 test locations per 1,000 square feet, and an additional 4 readings per 100 square feet thereafter, and average the results. In general, more readings will result in a more accurate average. Any unusually high or low moisture readings should be isolated and addressed individually. Record, date, photograph, and document all results. 2. The average of the wood subfloor readings should coincide with the manufacturer required temperature and humidity levels in the facility receiving wood flooring. (Refer to the MC chart in Part I of this chapter.) 3. Concrete subfloors must be moisture tested, and adequate moisture control systems should be in place prior to installation of any engineered wood floor. 4. Any unusually high or low subfloor moisture readings should be isolated and addressed prior to wood floor installation.

      D. Follow the flooring manufacturer’s moisture testing, acclimation, installation, and maintenance instructions to retain all warranty coverage.

      E. When the wood flooring is to the expected in-use (e.g., normal living) and manufacturer’s required ambient conditions within the facility, and this coincides with the subfloor moisture conditions, and these conditions are being maintained, the flooring may be installed immediately.

  5. Molly Hermes says:

    Jason,

    Thank you for your response. The engineered wood floors are installed on a raised pier and beam foundation. The crawl space is vented and dry. The bottom of the subfloor(1 1/8″) is insulated with closed-cell foam. The joists are not insulated. It looks like the floor installer used 15 lb felt paper for the vapor barrier. It also looks like the installer did not follow the nailing guidelines. The planks are not nailed within 2 inches of each end or every 4-6 inches. The rows were not always staggered 8-10″ row to row for the 5″ wide planks. So far the peaking is slight throughout the floor. Right now in Houston the weather has been cool and dry. Would you expect to see more distortion in the floor in spring and summer when the weather is more humid and wet?

    • Jason Wright says:

      Molly,

      It’s hard to say whether you will see more peaking in the spring. Typically during spring and summer, you have more humidity causing all wood to absorb moisture. This includes everything wood in your home. My suggestion would be to have an independent inspector come to your home and evaluate the situation. He will determine the cause of the peaking and provide a written, detailed report for you to follow up with.

      I hope this helps.

      Jason

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