How to Work With Fiberglass Over Foam

By Jay Kurz

Fiberglass is a very strong and durable construction material, used for many different applications. Some of the most common things constructed out of fiberglass are boats, showers, pools and industrial pipes. Fiberglass will bond to almost any surface, including wood, foam, metal and even plastic. For applications such as boats, the fiberglass is applied over foam. This is a fairly easy process that involves adding a fiberglass mat bonded together using fiberglass resin. All the supplies that are needed can be found at your local marine supply store.

Things You'll Need

  • Respirator
  • Fine grit sandpaper
  • Fiberglass mat
  • Fiberglass resin
  • Methyl ethyl ketone peroxide (hardener)
  • Small bucket
  • Stir stick
  • Felt roller
  • Air roller

Step 1

Sand the edges of the foam using fine grit sandpaper. Remove any uneven spots, and be sure the entire surface of the foam is smooth and flat.

Step 2

Blow off the foam to remove any loose foam dust. Any dust left on the surface can cause the fiberglass to bond incorrectly.

Step 3

Cut the layers of fiberglass mat to the specific size that is needed. Use a razor knife to cut the mat.

Step 4

Mix the resin and hardener following the directions on the containers. Use a small bucket and a stir stick to thoroughly mix the resin. It is important to mix the fiberglass and hardener very well. When the resin mixture is all one solid color, it is ready for application.

Step 5

Wet the surface of the foam using a felt roller. Cover the entire surface of the foam, so the fiberglass mat will stick to the foam. If you lay the dry mat on dry foam and then apply the resin, it will just lift up from the foam and take a long time to wet out.

Step 6

Apply one layer of fiberglass mat to the wet foam and wet the mat out using the felt roller. Add resin until the entire surface of mat is the color of the resin. Roll out the air bubbles using an air roller. Let the first layer of the mat harden. This is a base layer, needed so the fiberglass doesn't warp with too many layers added on top of the foam.

Step 7

Apply the remaining layers of the mat using the same process as with the first layer. Let the fiberglass cure until it's hard and cool to the touch. Sand the surface using fine grit sandpaper to remove any hairs or burs.

References & Resources