How to Fix and Prevent These 5 Problems in Hardwood Floors

 A lobby with a shiny oak hardwood floorHardwood floors are gorgeous, sturdy, and timeless. But one of their greatest enemies is water.

It can cause damage like:

  • The warping you noticed on your new floor when winter came around (because the installer didn’t acclimate the wood properly). 
  • Your floor lifting and detaching from the subfloor (because water pipes broke and flooded your kitchen while you were on vacation during the winter).

You’re probably already groaning!

Although water damage can be a hassle, don’t despair! We’re here to help you find solutions—at the source of the problem.

That’s why we’ll look at 5 types of damage and their causes. And more importantly, we’ll learn how to fix and prevent them:

  1. Cupping
  2. Crowning
  3. Cracking
  4. Buckling 
  5. Mold

Let’s begin!


Your wood floor is cupping if the lengthwise edges of the boards begin lifting and creating an uneven, concave appearance.

Cupping occurs when the bottom of the piece of wood is wetter than the top. There are many reasons for this.

Causes of cupping

Cupping has many possible causes, including:

  • Improperly dried wood at the time of installation. When the wood hasn’t reached the EMC (equilibrium moisture content) of the region, it will continue to swell or shrink once installed. 
  • Improperly dried subfloor (concrete or wood). The moisture in the subfloor can absorb into the flooring from underneath. 
  • Moisture in the crawlspace or basement. Especially during warm and humid times of the year, this moisture can rise from the ground and affect the flooring above.
  • Lack of a moisture retarder. A moisture retarder between the floor and the subfloor keeps moisture from penetrating.
  • Climate changes. A shift from a humid summer to a dry winter can affect the MC (moisture content) of wood if the indoor environment isn’t controlled.  
  • Leaks or spills. Water that spilled from an appliance can seep under the floor, causing the bottom of the wood to be wetter than the top.

Dealing with cupping starts with identifying the cause. We’ll look at that next.

How to fix cupping

Cupping, if caught early, may not require a complicated floor repair or replacement. Read on for factors to consider and steps to take.

1. Deal with the source of the problem.

The first step in fixing any moisture problem is to find the source and stop it.

So ask yourself: Is it a wet subfloor? Is it a leak? Is it just a seasonal climate change?

You’ll also want to figure out how serious the moisture problem is. How long has the moisture been there, and has it had time to soak into the floor or subfloor?

Get rid of excess moisture and clean the floor with a moist brush and mild detergent to prevent mold.

2. Measure the moisture levels of the floor and subfloor.

Once you’ve dealt with the moisture, you’re ready for the next step. Use a moisture meter to check the moisture level of the wood floor and the subfloor. Then compare that number with the EMC—your goal.

A yellow wood moisture meter for checking the moisture content of a wood floorKeep in mind that the MC of the floor should be nearly the same as the EMC. And the subfloor’s MC should be within 2 to 4% of the floor’s.

If the moisture damage isn’t severe and the MC isn’t far from the EMC, you can probably get away with not replacing the boards.

3. Dry the affected area.

Make sure that the floor (and subfloor) dries to the EMC. Depending on the source of the problem, you may also need to dry out the crawlspace or basement.

A dehumidifier and some good fans may help, as well as turning on the air conditioning or opening windows (as long as it’s not too humid outside).

If the cupping was caused by a simple climate change, drying the area may reverse cupping and solve the problem. Otherwise, proceed to step 4.

4. Sand and refinish the boards.

Even once you’ve dried your wood floor to the proper MC, you may still notice some unevenness. In that case, you can sand down the higher edges and refinish the boards. Many prefer to use a drum sander or random orbital sander for this job.

But note: Wait on sanding until the MC of the top of the board is within 1% of the MC of the bottom of the board. Otherwise, you risk having the opposite problem—crowning. (We’ll talk about that below.)

How to prevent cupping

Even better than fixing cupped boards is being able to prevent them in the first place. Here’s how:

  • Acclimate your flooring materials to the proper MC before installation. 
  • Use a moisture retarder between the floor and subfloor.
  • Make it part of your weekly routine to check for leaks around your appliances, such as dishwasher, sink, washing machine, etc. 
  • Fix leaks and clean up the water right away.


Crowning is when the lengthwise center of a floorboard lifts, creating a convex look. It happens when there’s more moisture on the surface than on the bottom of the board—the opposite of cupping.

Causes of crowning

If you’re dealing with crowning, check if any of these may be the cause:

  • Improperly dried wood at the time of installation 
  • Changes in climate 
  • Leaks or spills—even the bowl of water your cat keeps spilling!
  • Mopping the floor with water 
  • A cupped floor that was sanded too early because either the moisture issues were not fixed or the floor hadn’t completely dried

Let’s turn to some solutions.

How to fix crowning

A hardwood floor with a round, white cleaning robotThankfully, it may be possible to fix crowning without replacing floorboards. It depends on how bad the damage is.

The steps for solving crowning are similar to those for cupping.

1. Deal with the source of moisture.

Figure out the cause of the moisture, whether improperly dried wood, the climate, or a leak.

Make sure to remove any standing water by using a shop vacuum or a squeegee. Then, clean the floor with a brush and wood floor detergent to prevent mold.

2. Measure the moisture levels of the floor and subfloor.

Use your moisture meter. Compare the numbers you get with the EMC.

3. Dry the affected area.

A dehumidifier, fans, open windows, or air conditioning—do whatever it takes to get the air circulating so that the moisture can dry and the wood can reach its EMC. Check progress with a moisture meter.

If the crowning happened because of a climate change, proper drying may fix the issue. If not, move to step 4.

4. Sand and refinish.

The severity of the damage depends on the amount of water and how long it was on the floor. If the damage was minor, you can smooth down the crowned boards with sandpaper and refinish them—such as with a polyurethane finish. (Make sure they’re dry before sanding.)

A woodworker sanding some boardsHowever, if the unevenness is severe, sanding may not be enough, and you may have to replace the boards. Not ideal!

The good news is that the next section’s tips will help you prevent this kind of mess from happening again.

How to prevent crowning

Avoid crowning in your wood floor with these preventative measures:

  • Acclimate your floor and subfloor materials to the proper MC before installation.
  • Keep your home a consistent humidity and temperature.
  • Clean up leaks and spills right away.
  • Occasionally check for leaks around your appliances, such as dishwasher, sink, washing machine, etc.
  • Use cleaners designed for wood floors. And be sure to never pour liquid directly on the floor or use a sopping-wet mop or steam cleaner.
  • If you are fixing cupped boards, allow them to dry to the proper MC before sanding them.


Those lengthwise cracks in the middle of your floorboards? Not pretty—that’s for sure! Cracking happens when one part of the floorboard shrinks or swells, but the other part doesn’t.

Causes of cracking

The following are moisture-related causes of cracking:

  • Improperly dried wood at the time of installation. Perhaps one part of the board was dry, but the other part still had more moisture.
  • Rapid drying after a moisture problem. This can happen when someone is dealing with cupped or crowned boards.

How to fix cracking

Before you can fix the cracking and prevent it from happening again, you’ll want to figure out what caused it. We’ll start there.

1. Determine the cause of the problem.

The cause of the cracking determines the steps you’ll take to fix it.

For example, if the wood dried out significantly from the installation time, a humidifier may be necessary to maintain a better environment.

Cracked wood due to moistureBut if the floorboards weren’t dried properly, you may have to do that now. Use your moisture meter to keep track of progress.

2. Use wood filler in the cracks and refinish the floor.

If the cracking isn’t too bad, using wood filler and coloring it with a wood marker may do the trick. Then, refinish the floor so that everything matches.

If the cracking is major, you’ll need to replace the cracked boards and finish the new boards to match the others.

How to prevent cracking

Here are some simple steps to avoid ugly cracks in your flooring:

  • Acclimate your floor and subfloor materials to the proper MC before installation.
  • Keep your home a consistent humidity and temperature.
  • If fixing another issue (such as cupped or crowned boards), allow the area to dry slowly using a dehumidifier or fans. Don’t rush the process.


Buckling is a more extreme type of wood floor damage that occurs when the hardwood floorboards separate from the subfloor and lift—often many inches. It results from the wood not having space to expand in any other direction.

Let’s discuss the root of this issue.

Causes of buckling

Buckling usually has more significant causes:

  • Large leaks that result in standing water
  • Flooding
  • A wet concrete subfloor

Occasionally, the following installation mistakes can be factors too:

  • Improperly dried wood at the time of installation plus a significant seasonal shift in climate
  • Improper fasteners. The nails may not be the right size or distance from one another. Or the floor may not have enough expansion joints to allow for some shifting when the seasons change. 
  • Lack of space between boards for minor expansion (which is normal)

How to fix buckling

Though buckling is a serious problem, it’s not hopeless. And there are solutions aside from replacing the entire floor.

You’ve probably guessed the first step:

1. Deal with the source of the problem.

With buckling, the source will often be obvious: standing water. As quickly as possible, remove the water. The longer it has to soak into the floor, the more damage it will lead to and the more likely it’ll reach the subfloor.

At this point, you’ll also want to assess the type of water that has damaged the floor. Is it clean water? Or is it blackwater (sewage)?

If the latter, replacing the floor is a must to avoid health risks. And even if the water is clean, use a disinfectant to prevent mold.

2. Measure the moisture levels of the floor and subfloor.

A yellow wood moisture meter for measuring the moisture content of the floor and subfloorOnce you’ve removed the excess water, use your moisture meter to check the MC of the floor and subfloor. Compare that number to the EMC to get an idea of how much drying will be needed.

3. Dry the affected area.

Take up the buckled boards and allow them to dry. Also, dry the area underneath. If the subfloor is wet, you may need to put fans in the basement or crawlspace.

4. Reinstall or replace the boards.

If the buckling is not too severe, you may be able to reinstall the boards once they’re dry. But if the damage would be noticeable or the tongues and grooves of the floorboards are broken, the damaged area will need to be replaced.

How to prevent buckling

Emergencies—such as flooding or major leaks—happen, and sometimes there’s nothing we can do about them. The best way to prevent buckling, though, is to deal with standing water as quickly as possible. 

And here are some other steps you can take:

  • Acclimate your floorboards and subfloor materials before installation. 
  • Follow the installation procedures for your project. Use the correct fasteners, nails, expansion joints, glue, etc. Leave enough space for slight expansion that may occur in the wood. 
  • Keep an eye out for leaks.


A hardwood floor with white patches of moldMold is a fungus that thrives in a moist, warm environment, especially in humid areas (think the southern US). But mold should not be tolerated; it releases toxins that are harmful to human health.

Mold on your wood floor can appear like fuzzy, discolored (usually black or white) patches. Sometimes, the mold is sneaky, even growing under the paint. When this happens, the paint will need to be removed to deal with the issue.

Causes of mold

As mentioned, mold loves a warm and wet environment. Here are some ways a floor could become such a place: 

  • Leaks or spills 
  • Flooding

How to fix mold issues

Because of mold’s danger to health, we recommend that you skip DIY and hire a professional to remove the mold. The following reputable organizations can help you find someone: NORMI (National Organization of Remediators and Mold Inspectors) or IICRC (Institute of Inspection Cleaning and Restoration Certification).

Once you address the moisture and the mold, you’re ready to fix your floor. This will include drying the floor and applying a new finish coat (if you had to remove the paint).

How to prevent mold

Keep mold from growing with these preventative tips:

  • Acclimate floor and subfloor materials to the proper MC before installation. 
  • Deal with leaks and spills immediately!
  • If you’re fixing another type of moisture problem, clean the floor with proper disinfectants.

No more damage—and a wood floor you can be proud of.

The Bessemeter DS500, S300, and D300 wood moisture metersYou’ve got the rundown on the main types of wood floor damage: cupping, crowning, cracking, buckling, and mold. And you’re ready to handle them with confidence.

But honestly, who wants to waste time and money on damaged wood floors?

Not to mention that once a hardwood floor has been damaged, it may never be quite the same again!

So, take those steps of prevention, especially during installation.

Then, your beautiful hardwood floor will be a source of pride and joy for years to come!

Keep in mind that a high-quality wood moisture meter will be your best friend in making sure your floorboards are ready to go. Check out the Bessemeter shop to find one for your needs.