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Originally posted 15th April 2024

Last updated 17th April 2024

What Causes Wood Flooring To Become Cupped

What is wood floor cupping? Hardwood floors are very resilient, nonetheless occasionally issues can still...

Paul Hambidge

Managing Director Factory Direct Flooring Ltd

7 min read
Written by Expert

What is wood floor cupping?

Hardwood floors are very resilient, nonetheless occasionally issues can still crop up. It's never ideal to discover that your flooring isn't entirely correct, particularly when the damage is apparent like with cupped floors. 

Thankfully, floor cupping need not spell the end of the world—or your gorgeous flooring, for that matter. For owners of both solid and engineered hardwood floors, this problem is reasonably common. You can try your best to fix your flooring and stop cupping in the future after you understand what's happening and the source of the issue.

Cupping is the process of wooden boards being exposed to moisture from below or in the air causing the boards to warp and curve. More moisture on the underside compared to the top side of the board makes the wood’s edges curl up creating a ‘wave’ in your flooring. But don’t worry, the majority of the time cupping is reversible and can be solved with a few simple steps, and we at Factory Direct Flooring will show you how.

Example of how wood floors can 'cup' and start to bulge upwards

Wood floor lifting: what causes a wooden floor to cup?

Wooden floors cup due to an imbalance in the moisture content (MC) of the wood. With wood being porous it is susceptible to changing shape and warping if the internal MC changes. When the underside of the board receives more moisture than the top it causes it to swell and the centre to remain flat, giving the wood the U shape which leaves gaps between the planks. Many homeowners are left to worry about their flooring when cupping occurs. So what can you do? 

Subfloor moisture

Subfloor moisture is one of the main culprits for causing cupping and is even more prevalent in new builds. Excessive moisture in the concrete that the flooring will be installed upon will always warp the wood. If you have a damp basement or crawl space harbouring humidity, to prevent it from causing cupping, it’s worthwhile looking into a humidifier and keeping the relative humidity level between 30-50%. If the flooring is installed before any HVAC runs within your home cupping will likely become an issue you’re faced with unless preventative methods are installed. 

Insufficient moisture in engineered wood

We hate to be the bearer of bad news, however, it’s not just excessive moisture that can cause cupping. If the flooring installed in your house is engineered wood the boards can also be susceptible to dry cupping. What does this mean? Similarly to typical cupping, dry cupping is when there is a reduction in moisture on the top section of the boards. Even though no additional moisture has been absorbed by the bottom section of the wood the MC is still changing. When engineered wood flooring experiences dry cupping it can cause the layers of the wood to separate from one another. As the owner of an engineered wood floor, you will need to be careful when there is a significant reduction in moisture and possibly look to invest in a humidifier.

Uneven moisture exposure

Checking moisture levels before installation is the key to the longevity of flooring. There are many adequate electric moisture measurement tools available at DIY stores. By simply using this tool in multiple areas where the flooring is going to be installed you can foresee specific areas where there are higher levels of moisture exposure. Additionally, by testing your moisture levels before an installation you can save time and money as it will mean if you are outsourcing the fitting job to a tradesperson they will not need to carry it out themselves! By knowing these areas which have a higher chance of cupping you can prime and prepare the subfloor before the floorboards reach an equilibrium moisture content.

Installation errors

It’s not always the product's fault! Installation errors are a common factor in wood flooring cupping. If the subfloor on which the flooring is laid isn’t properly dried then the wood will absorb the moisture causing the underside to swell. If you are going to install your flooring and aren’t confident in ensuring that the subfloor is dry then looking to install an underlay beneath the boards is an effective way to eliminate the chance of cupping.

 

How to prevent your wooden floor cupping or bulging upwards

Whether you have just installed a beautiful new hardwood floor or have already had to deal with cupped wooden floorboards, you probably want to avoid it happening in the future. So here are some quick tips on preventing hardwood flooring from cupping:

Correct Humidity

Having the correct humidity in the room, and if applicable the room below, where the flooring is intended to be installed is a crucial part of how to prevent engineered wood and hardwood floor cupping. For reference, anything below 30% is too dry, and above 50% is too high - ideally, home humidity levels should hover around 45%. Luckily for you, there is no longer the need to open and close windows/doors for prolonged periods trying to get in-house humidity to the desired level (and with the current cost to keep your house warm your bank account will thank you also) instead humidifiers/dehumidifiers are a great way to track, alter and maintain humidity levels in your home.

Acclimatise your flooring

Acclimatising your flooring before installation is a free and easy preventative method for cupping and misshaping. But what is acclimatisation? It is the process of becoming accustomed to a new climate or new conditions; the goal of acclimatising your flooring is to allow the wood to familiarise itself with its new environment. It’s such an easy step in installing new flooring in your home however it is often overlooked and if not done can cause a lot of issues in the future. Whether the wood you’ve selected for your flooring is engineered or solid wood both must be acclimated to your home; the only difference? The amount of time you need to acclimate the wood. Engineered wood needs to be acclimated for 48 to 72 hours whereas solid wood needs up to 7 days. If you have any further questions or concerns on wood/flooring acclimation feel free to contact our team of experts at 0330 100 00 55.

How to fix wood floor cupping

Now you know what cupping is and the causes, let's talk about how to fix cupped wood floors as well as prevent and protect your fabulous new flooring from becoming cupped. There are 3 main ways to stop your hardwood floors from cupping and they’re so simple!

Clean and maintain

Floors are dirty as we brought to light in a recent blog! So actively cleaning your flooring should be a part of your cleaning routine. By cleaning your flooring you are removing dirt and possible moisture that is sitting on top of your wood flooring. However remember to never wet mop wooden floors with a traditional mop, all this does is massively raise the chance of your wooden floor absorbing excess moisture and possibly cupping. Instead vacuum, brush, or use a damp microfiber cloth either by hand or attached to the end of a brush handle. Routinely check flooring surrounding sinks, bathtubs, dishwashers, and any areas more likely to retain moisture - the earlier you catch it the easier it’ll be to fix!

Dehumidifier

In a world of technology of course some devices help reduce humidity and moisture content in the air. We’ve previously spoken about humidifiers and dehumidifiers but what are they and how do they work? 

A humidifier is a device that adds moisture to the air, which if you live somewhere that has very dry seasons, is a great tool to avoid dry cupping. On the other hand, a dehumidifier does the complete opposite, a dehumidifier works by removing moisture from the air to keep it at an ideal level for both you and your flooring.

Wood floor swelling from water damage or spils

Depending on the severity of the leak or flood it is unlikely a dehumidifier will solve the problem, so we’d advise you to contact a professional as they will have access to high-powered drying equipment which will highly increase the chance of the wood being saved.

 

Will cupped hardwood floors return to normal?

Now you know all there is to know about preventing and preparing your hardwood floors, if this is an issue will it return to normal? The short answer is YES! Once the wood has returned to the moisture equilibrium level the swell should decrease and the flooring will return to normal. However, we cannot say how long it will take, and will depend on the severity of the cupping issue. Future you will be glad to not have to deal with cupping and by making sure that the damaged wooden flooring problem is 100% resolved.

 

Conclusion

Remember most instances of cupping are reversible if it’s caught early enough and is treated correctly. Remember to make sure the subfloor is dried to a high standard to avoid moisture entering the wood from below, clean and maintain your flooring, look to invest in a humidifier or dehumidifier whichever suits your climate, acclimatise your flooring ahead of installation, and if the issue is severe call for professional help. For any more information check out our FDF Advice Centre.

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About the Author

Paul Hambidge, Managing Director

Paul has 32 years of flooring industry knowledge & experience from both an installation and manufacturing perspective. He started out as installer of very large commercial flooring projects for multiple retailers. As director of Factory Direct Flooring Ltd, he has been involved in all aspects of flooring and has worked with some of the largest producers of wood flooring, vinyl flooring and laminate floors.