Can MDF Take On A Coat Of Varnish? (+ Best MDF Varnish Revealed!)

Sealing MDF is a great way to make sure your brand new MDF furniture lasts for as long as possible.

With the proper protection, MDF boards can hold up for well over a decade. Yet, they will quickly warp and bow if you aren’t careful in keeping them away from moisture and humidity.

So, what can you do to make sure this doesn’t happen to your MDF furniture?

Well, one of the simplest ways to safeguard MDF is to coat it with a varnish wood finish. But, will traditional varnish alone be enough to shield this notoriously water-wicking material?

It can…but only if you use the right type of varnish.

So, in this post, you will learn why sealing MDF in particular is so important when it comes to this manufactured wood. And we reveal which type of special exterior-graded varnish pairs best with Medium Density Fiberboard.

mdf varnish

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What Can You Use To Seal MDF?

Most oil-based or solvent-based sealers will work well on an MDF surface. So, an oil-based varnish will coat onto MDF without issue.

However, as a rule of thumb, avoid using any water-based sealers on MDF.

This is because MDF is very easily water-damaged—thanks to all of the tightly bound wood shavings packed into this material.

Related Post: Can You Really Use MDF Outside? (Best Practice Revealed!)

And because MDF soaks up water so readily, it will soak up moisture from a water-based finish. And when that happens, the finish won’t have had time to properly dry and cure.

This, in turn, could create finish adhesion problems later on.

mdf varnish

And Can You Apply Varnish Straight Onto MDF?

Varnish will coat onto MDF, so feel free to apply 2 to 3 thin coats of varnish as a sealer.

But, it is worth pointing out that varnish is not just used as a way to seal wood. Varnish can also enhance the texture of natural wood too.

However, varnish won’t help an otherwise plain unfinished MDF surface really stand out.

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Do You Need To Varnish MDF?

If you want to protect MDF from water-damage, then a water-resisting sealer is an absolute must. However, it depends on what type of MDF surface you’re dealing with.

An unfinished MDF surface will need a sealer, such as varnish, to protect it. Yet, if that MDF furniture has come already finished, (say with a laminated covering or a coat of paint), then you don’t need to add varnish.

Related Post: Can You Use Linseed Oil On MDF? (What You Need To Know)

Does Varnish Make MDF Waterproof?

Only if you use an exterior varnish product. Traditional varnish, (made of resins, drying oils, and solvents), is typically used to seal interior wood items.

However, there is a type of varnish that’s designed specifically to seal exterior wood and marine lumber. Spar varnish is a waterproof version of varnish, (thanks to the Urethane contained in this product).

Urethane, (which is the same stuff found in polyurethane), not only makes Spar Varnish incredibly water-resistant, it also makes it more flexible than your standard varnish finish.

mdf varnish

So Then What Is The Best Varnish For MDF?

If you want a wrap MDF in a very water-resistant seal, then a Spar Varnish product, such as Rust-Oleum Marine Spar Varnish is your best bet.

This oil-based finish is specially designed to coat marine timber, yet it will readily coat onto an MDF surface too.

It takes just 2 hours to dry to the touch. And once it has fully cured, (which will take around 3 days tops), it will provide MDF boards protection from UV damage, moisture and any mildew growth.

You can find the latest prices for Rust-Oleum Marine Spar Varnish right now over on Amazon.

To Sum Up, Here Are The 3 Key Takeaways From This Post…

  • 1). MDF is easily water-damaged, so unfinished MDF should be coated with a water-resistant sealer.
  • 2). You can use varnish as an MDF top coat sealer (or as a primer on MDF surfaces).
  • 3). If you want to waterproof MDF, you should use an exterior Spar Varnish product.

References:

Payne, H.F. and Gardner, W.H., 1937. Permeability of varnish films. Industrial & Engineering Chemistry, 29(8), pp.893-898.