Why Is My MDF Board Warping? (+ How You Can Fix It)

One of the biggest woodworking myths is the idea that MDF boards cannot warp.

Sure, this manufactured wood can shrug off a bit of moisture. However, MDF is not water-resistant. And it’s core material is still made from hardwood and softwood composites.

Now, we all know that wood likes to move around if its exposed to a bit of water. And in extreme cases, this can cause natural wood boards to warp and twist.

So, is MDF capable of warping too?

MDF is less likely to warp compared to natural wood types such as Pine. However, MDF is only moisture-resistant, and it is not waterproof. So, MDF will soak up water, (just like natural wood), if it hasn’t been sealed on all sides. And as it soaks up water it will expand and contract, causing it to bow and curve.

Now if your stack of MDF has started to bow, then you’ve come to the right place. Why? Because if you keep reading, you will learn why that ‘unwarpable’ material is all bent out of shape. And you’ll also discover how you can both fix it and prevent it from happening again…

mdf warping

This post may contain affiliate links to products that we receive a commission for (at no additional cost to you). Learn more here.

Does MDF Warp Over Time?

MDF doesn’t warp like wood does. And thanks to its small-particle texture, it doesn’t split and crack like natural wood either.

Instead, this highly processed board tends to ‘bow’ rather than twist away (like say a warped solid wood door can).

Having said that, you’ll still want to keep MDF away from water and heat – and the general outdoors.

You see, if you don’t waterproof MDF, then moisture can easily get into those wood particles (especially through those ‘open’ edges) and cause issues.

And yet, if MDF has been properly sealed with a quality sealant, it can hold out pretty well against warping.

But that’s provided you don’t use it for furniture in high-humidity rooms, such as the kitchen or the bathroom.

Does MDF Warp Less Than Plywood? Plywood is stronger, more water-resistant, and more flexible, than MDF. All of these things combine to make Plywood less likely to warp than MDF.

How Do You Straighten A Warped MDF Board

Here’s the key thing about warped MDF; you need to catch the problem early.

That’s because once the curvature sets, (and the moisture inside dries out), you’ve pretty much lost your shot to straighten it.

However if you manage to catch it early – before the bowing sets in – you have a good chance at flattening that MDF.

Can You Really Flatten Warped MDF?

Yes, you can. You can flatten warped MDF out by simply weighting down the board. This isn’t a sure-fire way to get rid of that warping effect, but it is worth a shot.

Flattening MDF Board Using Weights:

  1. Lay two pieces of 2×4 wood across a work bench or table top.
mdf warping
  1. Lay the MDF board flat on top of the 2×4 battens with the MDF’s bowed curve facing up.
mdf warping
  1. Place a weight in the middle of the MDF board. The weight shouldn’t be heavy enough to break the MDF. Yet it should be enough to place downward pressure on the bowed curve.
mdf warping
  1. Every 30 to 60 minutes check back to see if the curve has flattened out.

Will 18mm MDF Warp? If it has been stored properly, then 18mm MDF boards won’t warp. However, if it has been soaked through or exposed to a lot of moisture, it can bow.

How Do I Stop MDF From Warping In The First Place?

Proper Storage/Handling

Typically, this is where a lot of MDF’s bowing/warping problems stem from. Water gets into the MDF somehow, or the area it is stored in becomes humid.

That’s why MDF, (especially boards that are unsealed), should always be stored away from water and moisture.

Edge Banding

Edge banding involves using a special type of tape to seal and cover up exposed edges of wood such as Plywood and MDF.

Simply apply moisture-resistant MDF edging tape to seal those over-exposed sides.

Apply Sealant

Sealing MDF is the simplest way to waterproof it.

If you plan on painting over MDF, then prime and seal all sides of it first with a thin layer of carpenter’s glue.

Also known as PVA glue, you will need to thin the glue out with water first. This will make it easier to apply onto MDF.

A mixture of 4 parts glue with 1 part water should be enough to thin PVA out – allowing you to brush it on.

Does Sealing MDF Wood Prevent It From Warping? Sealing MDF can protect it from warping. However, it won’t waterproof or weatherproof MDF from water or high-humidity.

Key Takeaways

Personally, no matter what project you’re working on, plywood is a much better option than MDF.

MDF might be cheaper than plywood, but, what you save in cost now you’ll pay for later with hassle.

Still, MDF can be used to make indoor furniture such as cabinets and small decorative pieces. And its void-free texture – unlike Plywood – makes it easy to work with.

So if you can flatten that MDF – and you take the extra time to seal it up right – warping shouldn’t be much of an issue.