How to level out cupped floorboards ready for engineered or laminate flooring

Cupped floorboards are a common problem and in most cases need to be addressed prior to installing an overlay wood floor. Here I’ll be giving some advice on how to level cupped floorboards ready for any overlay wood floor installation.

Before I start, it’s worth explaining why floorboards become cupped in the first place. Cupping is the result of the air moisture being greater underneath the floor boards and drier above. This has the effect of making the floorboards curl up at the edges on the drier surface. This can often be due to a lack of adequate ventilation underneath the floorboards. You should check that all air bricks are unobstructed and/or the cavity underneath the floorboards is clear of debris that could restrict air flow.

The moisture content above the floorboards can also be too dry. This can be due to air conditioning units drying out the air and even better sealed houses with ever advanced manufacturing methods of windows and doors. This isn’t to say that better window and door technologies are a bad thing as keeping the elements out will obviously be an advantage with heating costs, but a knowledge of this is worth having when trying to gain an understanding of why floorboards cup.

A possible third reason could be due to a leak or spillage of some sort for the surface of the floorboards to become wet. With an automatic response of trying to dry the floorboards out too quickly or even sometimes with natural drying, the floorboards can curl/cup.

How to level out cupped floor boards

The first step should be to sink all nails or screws below the surface of the floorboards. This can be an arduous task but an important one to prevent damage to machinery and blades/sanding discs. Sinking nails can be done using a centre punch and sinking screws can be done by using a cordless screwdriver.

Now there are two ways to remove the raised cupped wood from the edges of the floorboards. You could either use a drum sander with rough grade sanding paper attached or an electric planer.

Using a drum sander will require you to run the sander across the floorboards at a 45 degree angle. You will not be able to use the drum sander around the edges of the room so an edge sander will be more appropriate.

Levelling cupped floor boards with an electric planeUsing an electric planer is my personal favourite method. With a fresh blade attached, simply run over the high points of your cupped floorboards in the same direct as the floorboards (as illustrated in the picture on the right) until you have a nice flat surface.

With sanding or planing, in both cases you will not need to sand or plane the entire floorboard as the only requirement here is to bring the high points of the cupped boards to the same level as the middle.

Before and after of planed floorboards

Remember, they don’t have to look pretty as you will be covering them with an overlay floor covering. The objective is to just make them flat.

You can use a straight edge of any kind, like a spirit level or straight length of wood, by placing it at a 90 degree angle across the floorboards to gauge how flat they are. If your straight edge rocks or lets more than 1 mm or so of light show between where the straight edge meets the floorboards, then further sanding or planing is required.

Now you can safely install your new overlay wood floor covering with the knowledge that cupped floorboards will not effect the finished result.


© Copyright 2013 Wes, All rights Reserved. Written For: Fitmywoodfloor

I am a Pergo trained professional installer of 20 years. I've been up close and personal with lots of floors and have the knobbly knees to show for it...Should you have any questions or comments please feel free to add them below. Thanks for taking the time to call by and I hope the information you've found has given you some insight!........................................................................................................................................................................“When you click on links to various merchants on this site and make a purchase, this can result in the site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network,,,,,,, affiliate window network.” This statement is to comply with current internet regulations regarding transparency to consumers.

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