Have your hardwood floors started to curve instead of being flat? When wood floors make a wavy surface, it is called a cupped hardwood floor. Cupping can occur in all types of hardwood flooring.
Like buckling, moisture is the only culprit for cupping. That’s why hardwood flooring is less recommended by flooring experts in areas like Florida, where humidity is high. And high humidity means high moisture.
And the sad part is that cupping or buckling doesn’t come under a hardwood warranty for most brands. Also, taking professionals’ help would cost you $3-$8 per square foot.
Well, worry not because there are ways to return cupped hardwood floors back to good condition.
Before we get into fixing hardwood floor problems like this, let’s learn a bit more about cupping.
Types of Hardwood Cupping
There are several causes for your wood flooring to start to cup, but there is only one reason: moisture imbalance.
Wood is an anisotropic and hygroscopic material, meaning wood can swell or shrink with its grain orientation — you might have experienced that during seasonal changes. The extent of the shrinking or swelling is also directly proportional to its width.
If only one side of the plank is exposed to moisture, it makes the moisture content of one side different from the other. Therefore, it curls up the edges creating a concave structure called cupping.
Moreover, cupping will happen rapidly if you apply an impervious finish on the hardwood surface. This is due to the finish blocking the moisture from being vaporized. An impervious floor finish is normally used in hardwood to make it water-resistant.
Two types of cupping can occur due to the lack of moisture and due to moisture.
What Is Concave Cupping?
Concave cupping is the most common type of cupping. Basically, the surface of the boards will have a concave structure when it happens. This happens when the backside of the board absorbs moisture resulting in the edges being higher than the surface center.
What is convex cupping (Crowning)?
If the floor was not dried out enough before sanding and you sanded a concave cupped floor while installing the boards in the room, the upper surface will look flat while the edges become thin. When the boards become dry and return to their original shape, the edges become lower than the surface center. This makes the board surface convex and is called convex cupping.
To prevent it from happening, always check that the boards are flat and not cupped before installing. However, there is no other way than to replace boards in case of crowning.
Is hardwood cupping reversible?
To give a simple answer, yes. Hardwood cupping is reversible, but only in concave cupping. Currently, there are multiple ways to fix a wet, cupped hardwood floor. They can involve using different applications of dehumidifiers, or sometimes cupped boards can be flattened naturally over time on their own.
Unfortunately, when it comes to convex cupping, there is only one way to reverse the wood back to normal without replacing it to maintain a recommended level of humidity in the environment for a while. According to The National Wood Floor Association (NWFA), the relative humidity should be between 30 – 50%.
We know the reason for the cupping; what about the causes? Understanding the causes of cupping can help you prevent it.
Why Is My Hardwood Floor Cupping?
Cupping on hardwood floors can occur due to several factors. Wood floorings are not only the victim of cupping; you can also find cupping in laminate flooring.
Change in The Amount of Moisture in The Air
If you live in an area with extreme and sudden changes in seasons, such as humid summers and dry winters or vice versa, your wood will start reacting to the moisture in the environment.
If there is any change in moisture content in the surrounding air, hardwood will absorb or release moisture to attain equilibrium, i.e., it tries to match its moisture content with the surrounding air’s moisture content.
When the hardwood absorbs moisture and there is no space to expand, crushing the boards together, it cups.
Typically, cupping happens due to excessive moisture in the air, i.e., when the humidity is high.
Underlying Moisture Issue
If there is excess moisture in the subfloor of your flooring, that will cause the wood to swell or shrink.
If you have a crawl space, check if it’s damp; If it’s, your crawl space has higher humidity. Hence, the moisture is transferred from the crawl space to the subfloor and then to the hardwood floor.
There’re many reasons your crawlspace may dampen. it may be due to a plumbing leak or improper drainage of rainwater. It’s good to have relative humidity below 60% in the crawlspace.
Leaks or spills
Cupping that occurs due to a leak will generally be around an area with possible plumbing leaks, such as a sink or a dishwasher. While the top side is finished and a bit resistant to water, if the water seeps beneath the board, it can be absorbed by the floorboard, and the underside is unfinished.
Water on the hardwood floor left untreated or not appropriately cleaned will result in sudden cupping of the hardwood floor.
Firstly, if the hardwood floor is installed before the subfloor is adequately dried, it can cause cupping. For example, if a concrete subfloor has not been cured fully and you installed hardwood boards over it, the moisture from the concrete slab can transfer to the boards and cup them. Proper installation of hardwood is crucial in maintaining it in good condition.
Secondly, if no expansion gap is created while installing hardwood boards, the boards will push each other once they expand due to moisture. So, always have an expansion gap for the hardwood floor. Typically the expansion gap should be 10-15mm for hardwood flooring.
Finally, no or improper acclimation of wood planks can cause cupping of the wood flooring. Hardwood should be acclimated for a minimum of three days.
These are the major factors of hardwood floor cupping. If you have a case of hardwood floor cupping, here are some fixes for it.
How to Fix Cupped Hardwood Floors
Hardwood floor cupping can be reversed back unless it is damaged too much, in which case you might have to consider replacing the planks.
Identify the Type of Cupping.
We know that there are two types of cupping that can occur due to moisture. It is essential to recognize which sort of cupping you are dealing with to fix it.
Moderate cupping with a .01” to .02” heap can be reversed automatically over time. However, if the cupping is larger than this, consider fixing it.
You can take the help of a spirit level to check whether the floor has unevenness.
As I said earlier, convex cupping can’t be fixed. Convex wood floor cupping means the planks are damaged, and you must replace them with new ones.
Concave cupping can be fixed by following some simple steps below.
Can a dehumidifier fix cupping?
Yes, getting a dehumidifier can do wonders for your cupped hardwood floor. You have to ensure the hardwood floor is cupped, not water damaged. Set the dehumidifier to the highest extraction settings. Run it for at least 24-48 hours. Keep the humidity of the room below 60%. Sometimes, it may take an entire heating season.
The key to reversing a beautiful hardwood floor that has been wet cupped is maintaining the climate in your home for a while. Your cupped wood floors should return to normal.
If you have a crawl space under the subfloor and it’s damp, consider installing a dehumidifier there.
High-Powered Drying Equipment
If the cause of the cupping was a leak or a spill that was left untreated, excess moisture would remain on the floor or around the subfloor. This should be cleaned by a piece of high-powered drying equipment.
If you do not have a piece of high-powered drying equipment or cannot afford one, we suggest manually cleaning the hardwood and the subfloor with a disinfectant and drying them before putting them back.
Take help from flooring professionals if there is too much moisture and the boards are not getting flattened by dehumidifying.
Keep Humidity Levels Constant
The solution to wood floor cupping is a work of diligence. You must maintain a certain level of relative humidity levels in the area. Constant humidity level means constant moisture content in the surrounding air. The recommended amount of moisture levels for wood is between 8 to 12%. To measure the internal moisture content of the wood, get a moisture meter.
Remember, moisture is not bad for wood but tries to keep the internal moisture content in an equilibrium state as much as possible. This will be only possible with constant surrounding humid air.
Maintain the Floor Properly
You need to maintain a proper routine of checking areas for leaks and ensuring that all the spills are dried properly. Many cupped hardwood floors are caused by improper cleaning of the floors and untreated spills on the floors. If you follow a good care plan for your hardwood floors, you will not have a case of wet cupping.
If you feel that your cupped floors have been damaged beyond repair, it may be time to replace the boards.
It is not advisable to sand the floor and re-finish only the part of the cupped floor because that may make convex cupping. You should replace the damaged boards once the problem has been addressed.
Replacing the board should be done if you feel that the board has been damaged beyond repair. Remember that while the boards can be replaced quite easily, the new boards may start to cup or get damaged if you have not addressed the problem.
Always address and fix the moisture source before installing/ replacing new planks.
Remove the Molding/Baseboards
Sometimes, you may have to remove the hardwood floorboards adjacent to the wall. To access those hardwood planks, you will have to go through the molding. The molding is at the bottom corner of the rooms.
The moldings are usually glued to the wall or have some sort of locking mechanism installed in them. First of all, create a gap between the wall and the baseboards by tapping a putty knife with a hammer onto the caulking or glue.
Once you successfully create a gap, Use a pry bar and hammer to expand the gap and finally remove the baseboard molding.
To read a more detailed guide on removing baseboards, follow this link.
When you take the moldings off, remember or label each molding to its designated spot.
Replace damaged boards
If you want to remove hardwood planks damaged due to cupping, you need to remove multiple hardwood floorboards. Typically, cupping happens to multiple planks, not just a single plank.
Run a circular saw perpendicularly to the wood planks. Set the blade to a length deep enough to cut the boards, not the subfloor. Use a pry bar and a sledgehammer to take up the floorboards one by one. Keep repeating this until you remove all the damaged boards.
In rare cases, if you want to remove just one or a couple of boards from the middle of the room, follow the below steps.
Cut the hardwood board with a circular saw in 3 lines, one parallelly and two at an angle shown in the figure.
Then take the help of a pry bar or screwdriver to lift the hardwood cut pieces. Once you pull up a single cut piece, other pieces can be removed easily.
When you are about to place the new boards, make sure that you have already wiped away all the moisture and addressed the cupping problem. This is essential, or your new wood will end up damaged in the future as well.
Replace your wood floor with new hardwood planks.
Put Back the Molding.
Once you have returned to molding, you have successfully replaced your boards.
How to prevent hardwood floor cupping
During summer, humidity levels rise. This can result in cupping on your wood floor. Here are some tips to prevent cupping throughout the seasons.
Installation of a moisture barrier for your wood floors will keep them safe from excessive moisture, which can avoid cupping. The moisture barrier goes between the subfloor and the hardwood floors. This will prevent moisture from the subfloor from entering the wood floor.
Typically, an underlayment goes between the hardwood wood flooring and the subfloor. If the underlayment has a built-in moisture barrier, you don’t need to install it separately.
Install Acclimated Wood Floors
Before you install hardwood floorings, acclimate the hardwood planks for 2-3 days. This will help the planks’ moisture content to achieve equilibrium with their surroundings, and they won’t expand further.
The ideal range of moisture content in wood is between 6% and 9%. Outside this range, the wood can expand or contract dramatically. You can invest some money to buy a moisture meter.
Below is a chart showing the moisture levels likely to be found under a given temperature and relative humidity. The yellow-marked zone is the ideal zone.
Place the boards at a distance from the wood flooring so that the floor acclimates.
MC Variant Should Be Minimum
Make sure the moisture content variance between the floor and the subfloor is not greater than 2%. This can be measured using a moisture meter.
Fasten Floorboards Properly
Ensure that the floorboards are fastened properly because the wood will expand and shrink throughout the seasons. This will prevent cupping.
Install a Whole-House Dehumidifier
Whole-house humidifiers are said to remove excess moisture from the air. However, they are costly. A decent whole-house dehumidifier can suck from 6.5 pints to 150 pints of water per hour. Dehumidifiers will help maintain your wooden floors as they are for a long time.
Well, you have to buy an additional accessory, i.e., a humidistat that controls the dehumidifier according to the surrounding air moisture.
Damp-Mop the Floor
Since wood is porous in nature, it absorbs water. This results in water damage or expansion of the wood in bad condition. When cleaning the hardwood floors, be sure to damp-mop them. Static water on hardwood surfaces is a very bad idea.
Wood and moisture do not get along; moisture can cause issues other than cupping for the wood, so it is best to keep moisture away from wood. Take as many precautions as possible to ensure that the wood is free from all moisture and that you are practicing the right cleaning methods for hardwood.
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