How to Waterproof MDF

How to Waterproof MDF

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If you are building anything out of MDF , whether it is walls, a table, a deck, or anything in between, something that you need to be aware of is that it’s not exactly waterproof.

Medium-density fiberboard’s lack of water resistance is a problem that many people have to deal with, but thankfully there are some things that you can do to make it more water-resistant. Today we are going to teach you exactly how to waterproof MDF so that it will no longer let in water and rot.

Is MDF Waterproof by Default?

One thing that many people do not seem to know about medium density fiberboard is that it is actually not water-resistant or waterproof at all. Now, medium density fiberboard is moisture resistant, which means that it can resist moisture in the air, or in other words, it does fine in relatively high humidity levels.

However, moisture resistance or being resistant to humidity is not the same thing as being water-resistant, let alone waterproof. Medium-density fiberboard is in no way waterproof, and it’s not even very water-resistant. If MDF comes into direct contact with the elements such as rain or snow, it will begin to degrade. Specifically, medium-density fiberboard tends to swell and warp if it is in contact with water, especially for a prolonged period of time.

Once MDF swells and warps, it really won’t go back to its original shape, and may even cause structural integrity issues to occur. After a prolonged period of time of being wet, it will quite literally start to crumble and disintegrate.

The bottom line here is that medium density fiberboard is in no way water-resistant or waterproof, and therefore, if you don’t first treat it using the steps that we are about to outline below, you really can’t use it for any purposes that involve water, particularly not for outdoor use.

On a side note, there is a very special kind of medium-density fiberboard that is already waterproof when you purchase it. However, this is a very special kind, and realistically you are going to have a lot of trouble finding it, and moreover, if you do find it, it’s going to be very expensive. It’s actually going to be much cheaper to waterproof your own MDF than to buy MDF that is already waterproof.

How to Waterproof MDF

Now that we know that your average medium density fiberboard isn’t waterproof or water-resistant, we can now move on to talking about how you can waterproof it. The only real way to waterproof MDF is to first prime it and then apply a waterproof or water-resistant paint, sealant, varnish, or lacquer.

Step 1: Gather Your Materials

First off, you need to go purchase all of the materials that you will need in order to complete this task. Here you will need a paintbrush as well as a paint roller and a roller tray. You will also need a latex primer that is designed to work with medium-density fiberboard, as well as your choice of water-resistant paint, stain, lacquer, or varnish. If at all possible, go for paint that is labeled as being 100% waterproof, not just water-resistant. Once again, water-resistance and being waterproof are not the same thing.

MDF Primer

Step 2: Prepare the MDF

Before you start applying anything to the fiberboard, you do first just want to clean it off. Take a damp rag, but not too damp, and just wipe it down to remove any dust. Wait a few minutes for it to dry and then use a brush or even a vacuum to suck up any remaining debris. You do not want any dirt or debris under the primer once you go to apply it.

Step 3: Apply the Primer

With the medium-density fiberboard ready to go, you now want to pour a good bit of the primer into your paint roller tray and then use your paint roller to apply an even layer to one side of the MDF. Depending on the exact primer being used, it’s going to take a while to dry. Once it is dry, you can then flip it over and do the other side.

Remember that you also need to use your paintbrush to apply a coat of primer to all four edges of the MDF. Once the entirety of the MDF has been covered in primer, you just then need to wait for it to dry and then move on to the following step. Unless you plan on wasting money by using two sets of painting utensils, you do now also want to wash off your brush and paint roller.

Step 4: Apply the Paint

Just like you used your brush and paint roller to apply the primer to the MDF, you now just want to repeat this process with your waterproof paint of choice. Of course, this could also be a varnish, stain, or lacquer. Apply the waterproof paint to one side, let it dry, then flip the MDF over and apply the paint to the other side, and then finish it off by using your brush to apply the waterproof paint to all four of the edges. You can now let it totally dry.

Mistakes to Avoid, Tips & Tricks

With the process out of the way, here are a few more tips on how to waterproof MDF efficiently:

  • Paints that are labeled as being 100% waterproof usually aren’t actually totally waterproof, which means that it is definitely recommended that you apply a second layer of the waterproof paint.
  • If you only need one or two pieces of waterproof MDF, then it may actually be cheaper to just buy it waterproof instead of using money on painting utensils, paint primer, and more.
  • Always wear old clothes when working with paint because you are bound to get it all over yourself.


Now that you know everything there is to know about waterproofing MDF by yourself, you can get to using MDF for all sorts of tasks that involve a lot of water and moisture.