How to Waterproof Hardboard

How to Waterproof Hardboard

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Hardboard is a fantastic building material to consider when it comes to making furniture, small objects, and decorations. It may also be used for wall paneling and other such applications. That said, hardboard does come with some concerns in terms of moisture.

o, hardboard is nowhere near as water-resistant as something like a solid piece of hardwood. Luckily, there are some things that you can do to help make your hardboard a bit more moisture resistant.

Is Hardboard Waterproof by Default?

Although hardboard does make for a decent material, one fallback that it has is that it is definitely not waterproof. Moreover, regular hardboard is not even really water-resistant at all. Hardboard is not a material that you want to use for exterior purposes because it will absorb moisture and it takes a fairly long time to dry.

Hardboard is made out of small wood fibers and as they get wet, they will swell, thus changing the shape of the hardboard sheet. Moreover, as the fibers in the hardboard continuously swell and expand and then dry and contract, it will affect the overall integrity of the material. In other words, it will quite literally start to fall to pieces. Therefore, if you plan on using hardboard for anything to do with moisture, you definitely need to waterproof it.

How to Waterproof Hardboard: Three Methods

There are three main methods that you can use to make hardboard waterproof, or at least more water-resistant.

Method #1: Using Paint

The first method for making hardboard waterproof is to simply paint it with waterproof paint. Follow the steps as outlined below in order to waterproof hardboard with paint.

Step 1: Choose the Right Paint

The first thing that you will need to do here is to choose the right paint. In other words, in order to make the hardboard more waterproof, you will definitely want to go with an oil-based paint that is rated as being waterproof.

Step 2: Prepare the Hardboard

To ensure that the paint adheres to the hardboard, you will first want to lightly sand it. Sanding the hardboard will create a slightly coarse surface for the paint to properly adhere to.

Step 3: Paint

Now use something like a basic paint roller to apply a relatively thick coat of paint to the hardboard. Remember that you need to get both main surfaces of the hardboard as well as all four of the edges painted. Allow the paint to dry for as long as it’s recommended by the product packaging.

Step 4: Paint Again

To really make the hardboard as waterproof as possible, add a second layer of your waterproof paint.

Method #2: Using Sealant

OK, so what needs to be said about using paint to make hardboard waterproof is that you will be of course changing the color of the hardboard. That said, if you have a piece of hardboard that already has the color that you want then you will not want to paint it.

Instead, you will want to use a sealant in order to make the hardboard waterproof without changing its overall appearance. For this method, we are not going to provide you with a step-by-step tutorial because it is exactly the same as the one above. Using a waterproofing agent or sealant on your hardboard is no different than painting it.

Method #3: Using Waterproof Sheeting

Although this final method is not all that common, it is definitely an option to go with. If you have hardboard in a high traffic area such as a wheelchair ramp that many people use on a daily basis, you may want to cover it with some kind of tarp or sheet in order to make it more waterproof and to protect the hardboard underneath.

Step 1: Get Some Tarps or Sheets

There are special sheets available for purchase designed just for this purpose. You want to go find yourself special waterproof tarps designed to be attached to wood.

Step 2: Lay the Tarp on the Hardboard

You will now want to lay the tarp on the hardboard sheet, making sure that it is the proper size. Once you have it laid on the hardboard, cut the plastic sheets down to size so that the edges of it are just large enough to reach the back of the sheet, so you can then attach it to the rear.

Step 3: Use Waterproof Epoxy and a Staple Gun

If you want to make sure that that waterproof sheet is going to stick permanently to the hardboard, you want to use a combination of waterproof epoxy and a staple gun.

Lay the sheet of plastic on the ground, put the hardboard on top, and fold the edges of the tarp over the sides of the hardboard. Apply the waterproof epoxy to the rear of the hardboard, just around the edges on the backside, and then press the plastic into it. You may need to weigh it down to ensure that the epoxy bonds with both materials.

Once the epoxy is dry, which could take up to 24 hours, go around the edges of the hardboard with a staple gun.

Mistakes to Avoid, Tips & Tricks

Lastly, below are a few tips to get the job done more efficiently:

  • When painting or sealing hardboard, make sure to do so in a well-ventilated area, and wear a mask or respirator if needed.
  • When working with dangerous substances, such as sealants, wear gloves to protect your hands, and preferably protective goggles too.
  • Never do any painting when it is super humid or even raining. The air needs to be fairly dry for this.
  • In all reality, using hardboard for any exterior application is just not a good idea.


We hope that our guide on the three methods at your disposal for hardboard waterproofing has been able to help!

As you can tell, waterproofing hardboard is not overly difficult, but if there is to be moisture involved, it is necessary.