How to Waterproof MDF

One of the most versatile construction materials available, Medium Density Fiberboard (MDF) is also inexpensive and fairly durable – making it a favorite of carpenters and DIYers alike.

Commonly used as a “plywood replacement”, particularly when weight is a concern, MDF is easy to work with, has a smooth easy to finish surface, and has plenty of strength when used correctly.

At the same time, MDF does have a bit of an Achilles heel that has to be accounted for. We are talking about water, humidity, and moisture!

Even just a few drops of water on MDF can cause it to swell up. Even high levels of humidity over an extended amount of time (like untreated MDF in a bathroom, for example) will cause the cellular structure of MDF material to dramatically expand – busting and popping apart quite literally at the seams.

A lot of this has to do with the way that MDF is made.

A 100% manufactured material, MDF (if you really boil it down to its basics) is little more than a composite of sawdust and glue that has been fused together after being exposed to tremendous heat and a lot of pressure.

The second that water or moisture comes in contact with unprotected MDF material the sawdust acts as a sponge, drawing in just as much of the water or moisture as possible and destroying the material itself.

Luckily, though, there are ways to avoid that as soon as you learn how to waterproof MDF going forward.

How to Waterproof MDF

Can MDF Be Waterproofed?


Not only can MDF materials be waterproofed, but the general process for waterproofing MDF is relatively simple and straightforward.

For starters, MDF is almost always “wrapped” with a harder laminate exterior that protects the interior sawdust and glue composite. This laminate shell provides quite a bit of protection against water and moisture, even if it hasn’t yet been painted or sealed.

The trick, though, is making sure that any of the exposed edges of MDF are also treated and sealed up. It’s these exposed components (like the exposure caused by cutting into MDF, for example) that are going to cause trouble.

Those other factors that water and moisture will use to get into your MDF, expanding the sawdust and ruining the profile and structural integrity of your material at the same time.

Why Waterproof MDF in the First Place?

The number one reason to learn how to waterproof MDF is to prevent that structural breakdown from happening whenever possible.

As highlighted earlier, MDF is a very lightweight and inexpensive material that is also easy to work with – but it loses a lot of its luster (and almost all of its strength) when the sawdust mixture becomes compromised from water exposure.

Worse, it doesn’t take much water or a lot of extra humidity to destroy otherwise perfectly good pieces of MDF!

By sealing and protecting your materials this problem disappears completely, though.

How to Waterproof MDF

Important Things to Consider When Waterproofing MDF

Before we highlight a few of the best products used to waterproof MDF, it’s important to consider a couple of details that will influence how you go about waterproofing the material you’re working with specifically.

How Much Water or Moisture Will MDF Be Exposed To?

There’s a world of difference between the waterproofing process involved in protecting and preparing MDF that’s going to “live” primarily indoors and away from water sources and humidity (like crown molding, for example) and MDF that’s going to be placed outside in the wind and the weather.

Think about how much water and how much moisture your MDF materials are going to be exposed to before you hunt for waterproofing solutions.

Paint or Stain Finish?

Secondly, you need to think about how you’re going to finish your MDF material as well.

Some waterproofing solutions work well with painted finishes, others allow you to get a gorgeous stain on your MDF, and others still are going to work regardless of the type of finish you are after.

Protect Exposed MDF Edges

Finally, you have to be sure that you are not just “face treating” MDF that you are working with but are instead protecting any exposed edges and potential vectors for water damage.

A lot of people make this mistake and discover their MDF bubbling and bowing (and sometimes flat-out disintegrating) after they have waterproofed it, only to realize later that they left cut edges exposed and unprotected.

Don’t let that happen!

Products That Work to Waterproof MDF

1. Kilz Adhesion High Bonding Latex Primer and Sealer

Kilz Adhesion High Bonding Latex Primer and Sealer


  • Interior/Exterior water based multi-surface bonding primer
  • Seals porous surfaces
  • Bonds to a variety of “tough-to-paint” surfaces

One of the best bonding primers on the market today, this paint like material has a high level of adhesion that guarantees to “stick” to MDF – not just on the cut and exposed areas of the MDF material you are working with, but on the laminate services as well.

Definitely intended to be used with a painted topcoat, this base layer offers top-tier waterproof protection after it has been given time to dry and cure. Water will literally bead up and slide right off your MDF when this primer sits beneath your paint.

2. JetCoat Farm Pride Acrylic Outdoor Paint

JetCoat Farm Pride Acrylic Outdoor Paint


  • Acrylic water-based formula
  • Livestock-friendly
  • One coat coverage

An acrylic paint formula (available in a handful of different colors), this paint is heavy, thick, and intended for exterior purposes only – a paint designed to stand up to everything Mother Nature can throw at it and then some.

Not only is this paint waterproof for MDF applications but it’s also mold resistant and environmentally friendly. Heat and UV sunlight won’t break down the protection that this pain provides, either.

3. Krylon Clear Coat

Krylon Clear Coat


  • Protects against harmful UV light rays
  • Non-yellowing, permanent coating
  • Moisture resistant

A clear coat in a canned solution, this spray on clearcoat is going to provide top-level waterproofing protection for MDF applications but it’s also going to create a “hardshell” on the MDF that protects from other types of damage, too.

The coolest thing about this material specifically is that it dries in just a few minutes, locking out moisture right away, and offers great UV light protection as well.

A permanent sealant, it doesn’t yellow as it ages the way that some other clearcoat options may.

4. Rain Guard Water Sealer Clear Coat

Rain Guard Water Sealer Clear Coat


  • High gloss sealer
  • Safe to use
  • Long Lasting and Water based sealer

If extreme protection against water damage and humidity is important (for MDF applications in bathrooms where things can get pretty steamy or for exterior uses of this construction material) nothing beats Rain Guard water sealer.

This waterproofing is engineered to provide up to five years of waterproofing protection, UV ray protection, as well as a hardshell protection against dirt, salt, and other weathering as well.

Closing Thoughts

At the end of the day, as long as you focus on the details provided above finding the right solutions to help you waterproof your MDF (for any application imaginable) should be pretty simple and straightforward.

Just remember to think about how you want the finished product to look, that you protect any cut or exposed edges, and that you invest in a quality waterproofing solution and you’ll be good to go.

With proper waterproofing you’ll be amazed at just how much more versatile MDF becomes!