The most common reason for wavy hardwood floors is moisture that leads to cupping, or warping of the wood. A simple change in the weather can reveal wavy hardwood floors. Obviously, something as drastic as a flooded floor will also create water issues. But, wavy floors are usually caused by something a bit more subtle.
Humidity is the likely culprit that can cause the moisture content of your floor to change.
The humidity level inside the home often happens due to temperature control of air conditioning or heating units. The humidity is intensified if the wood flooring is set on top of concrete, above a crawlspace, or if proper moisture testing was not done before the installation was complete.
What Causes a Hardwood Floor to Appear Wavy?
Hardwood floors consist of a hygroscopic material, meaning they tend to absorb moisture, humidity, and all forms of wetness, from the air or from the subfloor.
While moisture is at the root of all wavy hardwood floor issues, the reason the floor becomes wavy may be due to a few deeper factors causing it to happen.
Imbalance of Moisture
While moisture is the root of the problem, it is the imbalance of the moisture that causes the wood to respond and look wavy. The bottom of the floor typically has more moisture than the top.
Inside Air
If the air in your home is very dry, which often happens in the winter or is caused by air conditioning in the summer, moisture can become trapped under the floor.
The most common forms of wavy hardwood floors are listed below.
Cupping
As the name implies, when wood gets wet, it swells and begins to form a cup-like environment, or indentation, toward the middle of the floor while it rises up around the edges. When wood takes on moisture, it begins to swell.
When the hardwood in the flooring swells too much, you will start to see individual boards begin to push out around the edges and curve to become higher than the center of the floor. Cupping will cause a hardwood floor to look wavy.
Crowning
Crowning is the opposite of cupping. Instead of the edges becoming higher, with crowning, the center begins to rise higher than the rest of the floor. Crowning indicates that the moisture buildup is located toward the center of the floor.
Sometimes, when you sand a board that had been cupping to make it lie flat, the board starts to crown as moisture levels change.
Warping
Sometimes warping is referred to as buckling. Warping happens when the subfloor contains excessive moisture that may have come from the subfloor or from a leak or from another form of flooding. The subfloor begins to evaporate its moisture and the hardwood floor that sits on top of it will absorb it.
Warping may cause the wood to start to pull away from the subfloor. If water damage is severe, the boards will separate and peel several inches, centimeters, away from the subfloor below.
How To Repair a Wavy Hardwood Floor
The best time to keep hardwood floors from becoming wavy is to properly install them by first performing pre-installation moisture testing, and using a vapor barrier and plenty of ventilation to allow the moisture to subside and completely dry.
Ideally, there should be 1.5% open venting and cross-ventilation per 1,000 square feet, 92.90 square meters, of flooring. Unfortunately, many construction projects are rushed and not always done the way they should be to prevent future issues after installation.
The good news is that if you catch the problem early, it’s possible to repair a wavy hardwood floor and restore it to a usable and aesthetically pleasing condition. Also, cupping is actually a less serious form of damage than warping and is usually able to be repaired.
Following are some methods for noticing warning signs of moisture, and repairing a wavy hardwood floor:
- First, find the root of where the moisture is coming from before you can address the problem to fix it. You can change your air comfort habits, or use humidifiers and dehumidifiers to adjust depending on moisture levels.
- Water Droplets – If you notice water condensation that shows up on the wood floor with no apparent reason, it’s time to pay close attention and test for moisture to find where the wetness is coming from.
- Musty Smell – If you notice a musty odor, there could be mold or bacteria underneath the flooring.
- Discoloration – Sometimes, too much moisture may cause a discoloration of the finish on the wood.
- Pest Infestation – If you notice termites or other pests suddenly showing up, they could be drawn to the moisture.
- Hygrometers and Thermometers – Hygrometers and thermometers should be used to test different areas of the subflooring before even thinking of installing a hardwood floor on it.
- Check RH – RH stands for relative humidity. Check for RH conditions with a thermo-hygrometer.
- Measure for Moisture Content – Make sure you properly identify the moisture issue before repairing or completely replacing the floors. Get a quantitative measurement of the moisture content, %MC by using a moisture meter.
- Probe-type Moisture Meter – A probe-type moisture meter measures electrical resistance down into the subfloor using 1 1/8” penetration electrodes to compare the top 3/16” of wood to the bottom of the wood as well as the subfloor. If there is a moisture imbalance of more than 4%, there is a moisture problem.
- Stabilize Moisture Balance – It’s best to stabilize moisture levels between the subfloor and the wood floor. To do this properly takes time. Sometimes, it can take an entire year of air conditioning and heating use to equalize the moisture levels.
- Sanding – Once you have the moisture levels under control, you will need to sand the floor and refinish it.
When To Get Professional Help
If your hardwood floors have been exposed to moisture for a long time, and you didn’t notice, the damage may be beyond an easy fix. The floor may be so waterlogged that it’s time to replace it with an entirely new floor.
Before doing so, you will need to have an expert come in to remove the flooring, test for moisture content, and remedy the root of the problem before pouring money into a new floor only to have the problem persist months down the road.
Also, if water has built up and never completely dried, there could be mold or mildew forming or already out of control. Mold, mildew, and bacteria left unnoticed can also weaken the wood.
If you notice a mold issue, you will probably need a professional to remediate the mold before laying down a new floor or trying to salvage the one you have after the mold is cleaned up.
Final Thoughts
Of course, the best way to avoid wavy hardwood floors is to combat any moisture issues from the start, before the floor is set in place. If your wood floor is looking wavy, it’s time to find out where the moisture is coming from that is causing it to show signs of cupping, warping, or crowing.
If you know what signs to look for and catch the damage early, know how to test for moisture content and relative humidity, and expect a fairly easy repair. Otherwise, be prepared to call in a professional.