How to Waterproof MDF

MDF, while an affordable and versatile woodworking material, is notoriously susceptible to water damage.

This post will show you how to waterproof MDF using an easy process to be used in humid environments or outdoors.

This method will protect your MDF from water damage and increase its durability and lifespan.

Let’s get started!

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Is MDF Naturally Waterproof?

MDF, or medium-density fiberboard, is engineered wood made from heat-pressed wood fibers. It’s known for being strong and dense yet easy to work with and cut.

However, one downside of MDF is that it’s very susceptible to water damage.

When MDF gets wet, it can swell, warp, and disintegrate. Waterproofing MDF will protect it from moisture and extend its lifespan.

Weatherproof vs. Waterproofing MDF

If you’ve ever tackled a home improvement project, you’ve likely come across the terms “weatherproof” and “waterproof.”

Though these terms are often used interchangeably, there is actually a big difference between weatherproofing and waterproofing. 

Weatherproofing refers to making a material resistant to weather effects, such as sun damage or mold growth. 

On the other hand, waterproofing means making a material impervious to water. So, if you want to protect your MDF from the elements, you’ll want to weatherproof it.

And if you’re looking to protect your MDF from water damage, you’ll want to waterproof it. Of course, the best way to protect your MDF is to do both!

How to Apply Waterproofing Sealant to MDF

To waterproof MDF, you’ll need a waterproof sealant. We recommend using a clear polyurethane sealant, like this one from Minwax.

Minwax Fast Drying Polyurethane Protective Wood Finish, Clear Semi-Gloss, 1 Quart
  • PROTECT WOOD SURFACES – Minwax Polyurethane Wood Finish protects interior projects like woodwork, furniture, floors and cabinets. The oil-based, clear top coat is one of the most durable coatings for wood protection against scratches, spills and more.
  • OIL-BASED DURABLE FINISH – Clear finish provides long-lasting protection and warm beauty to both finished and unfinished wood projects. Protective coating is ideal for woodwork, furniture, doors, cabinets & floors, and is available in a variety of sheens.
  • SEMI-GLOSS SHEEN – Give your wood projects a sleek finish with this semi-gloss clear varnish. It not only protects the natural beauty of the wood, but offers a long-lasting, semi-shiny, sleek sheen for a modern look.
  • FAST DRYING – Get more done with this protective poly coating. It’s a fast-drying clear coat, which allows for quick recoats after 4-6 hours, letting you get projects done faster. Be sure to apply with a high-quality natural or foam brush.
  • A BRAND YOU CAN TRUST – Minwax is America’s leading brand of wood finishing and wood care projects. Since 1904, we have been inspiring consumers to Keep on Finishing. We offer consumers a complete line of products to meet every wood finishing need.
  1. Sand the surface of the MDF to ensure maximum adhesion.
  2. Next, apply a thin sealant layer to the MDF using a paintbrush or roller. Make sure to get into all the nooks and crannies.
  3. Allow the sealant to dry completely, then apply a second coat.
  4. Once the second coat is dry, your MDF piece is now waterproofed!

Tips for a Long-Lasting Waterproof MDF Seal

To ensure your waterproof seal lasts, follow these tips:

  1. Apply the sealant in a well-ventilated area.
  2. Use a high-quality sealant designed for waterproofing.
  3. Apply at least two coats of sealant, allowing each coat to dry completely before applying the next.

Waterproofing MDF Frequently Asked Questions

Is MDF waterproof if painted?

While we recommend using a clear polyurethane sealant, you can also use a waterproofing paint or primer. Just make sure it’s designed for waterproofing and follow the manufacturer’s instructions.

Is MDF ruined if it gets wet?

If MDF gets wet, it can swell and break down. In addition, water can cause the resin binders to deteriorate, leaving the wood fibers vulnerable to damage. As a result, it is important to take care to avoid getting MDF wet. If your MDF becomes wet, you must dry it out as soon as possible to prevent further damage. You can do this by setting up fans or dehumidifiers in the room where the MDF is located. Once the MDF is dry, you may need to sand it down or replace it entirely, depending on the extent of the damage.

Can MDF survive outdoors?

MDF is not meant for outdoor use. Engineered with wood fiber, resin, and wax, the material will degrade quickly when exposed to direct sunlight or high humidity. The porous surface of MDF also makes it susceptible to mold and mildew growth.

Can you use exterior paint on MDF?

Yes. First, seal the MDF with a primer designed for porous surfaces. This will help close off the MDF’s pores and create a smooth surface for the paint to cling to. Next, choose an exterior paint that is suitable for use on wood. Apply several coats, allowing each one to dry thoroughly before adding another.

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