How to prepare tempered hardboard for painting surface

by Laure Locascio November 19, 2024

Note: This is just to share experience and not to promote one method over another.

Tempered Hardboard panel

Tempered hardboard panels used for painting with acrylics - Pros and Cons

Cons

1. Requires 3-4 applications of gesso

2. Reverse side must be sealed if in high humidity climate

3. Can warp

4. Must seal back side and edges

Pros

1. Smooth surface

2. Easy to paint on surface

3. Easy to frame

4. Can use THB panels as backer board when framing

How do I seal the back side of the panel?

(This is only what I have tried so far/not promoting any particular brand)

• Use a sealant. Optional sealants are listed below. (No preference, no promotion)

• Use a brush because the back is not smooth and will tear up a foam brush.

• Use a bristle brush or chip brush. (Available at big box stores) These are inexpensive, and you will be using this to seal, not to paint.

• The panel will soak up the sealant quickly.

• Let dry according to sealant instructions.

  • Optional Sealants

    • Shellac (dries overnight)

    • Olympic water guard (has mildew resistance)

    • Urethane (can use indoor water or oil based)

    • Varnish (can use Liquitex, but it can be expensive)

    • Epoxy (I have not used this, but have seen others online using epoxy)

In the image, you can see the board that is lighter in color, or the board on the left is not sealed. The board on the upper right is sealed.

Back Side of Tempered Hardboard Panel

In this image, you can see the board on the left is not sealed, and the board on the right side is sealed. When you weigh the boards, the board on the left is lighter in weight than the board on the right.

I use the gesso application to seal the edges. You can observe the board that has a single application of gesso is darker in color.

I hope this helps.

My work area is still suffering from Hurricane Beryl and the humidity is really high from leaking roof and open ceiling. I didn't notice warping before until the humidity reached over 63%. Also, there is not a lot of information online about using THB for painting surface, so I just wanted to share in case someone else had questions.

If you have any ideas, or recommendations, please feel free to share so that we can all learn together.