Building a custom hatch with a one off mold

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The following depends on a lot of things, thickness you want, size of actual hatch, finish desired, non slip surface built in mold or done after popping out hatch of mould.

Mold Ingredients:

3/4" Plywood (cheap stuff good on one side)

1 sheet of Formica brand or equivalent (Shinny, smooth surface)

Contact cement

1.25" Wood screws

Mold release Wax

Non drying Clay to radius mold corners

Hatch Ingredients:

Gelcoat (No Wax) and MEKP Hardener

Fiberglass Mat 1.5 oz

1708 Biaxial

Some kind of radius tool

Some kind of core (Plywood, Balsa Core, Coosa Board, PVC Board, Divinycell, XCell Honeycomb, etc...)

Fiberglass bubble roller to roll out air bubbles

Brushes to apply resin and gelcoat

Buckets for mixing resin and gelcoat

Acetone to clean brushes and roller.



Polyester Resin & MEKP Hardener

Cut strips for the thickness of the hatch

The left over piece of Formica/plywood will be the mold surface for the hatch, it is going to be to top surface of your hatch when you pop it out.

Remember with this style mold, you are building the hatch from the outside in.

Attach strips that you cut for the height of the hatch to the large flat section to the size of the hatch you want.

So lets just say the finished hatch has to be 12" x 24" x 1" high.

Your mold side strips will be cut at exactly 1" and will be mounted on top of the large piece.

The large piece will have to be larger then 12" x 24" because the side pieces are getting mounted on top.

The center is the actual size of the hatch. The mold pieces need to be cut to match those measurements and be able to screw or glue it together.


If the large piece is exactly 12" x 24" you won't be able to attach the side mold pieces to the surface or else you will lose 1.5" from the mold thickness of the side pieces. If you did cut your mold to exactly 12" x 24" you will have to attach the side mold pieces to the sides or else you will lose 1.5 inches

Hopes this makes sense. See Picture above

Once your mold is screwed, glued or attach to the size you want, you will get the high temp mold wax and wax the surface. The TR High Temp Mold Wax is a great product to use. 1. Apply, 2. let dry 20 minutes 3. wipe off 4. Let sit 30 minutes.

Repeat steps 2 more times waiting 30 minutes between coats after wiping wax off..

It is very important to wait 30 minutes between coats. The 30 minutes starts after you wipe the wax off.

Once your mold is waxed it is time to make the clay radius. Start by washing your hands. start rolling wax with the palm of your hands into a pencil size cylinder shape. Apply the cylinder clay to all corners of the mold pushing it into the corners a little.

Use your homemade clay radius tool to make a radius in all corners. A sphere works best and wont change the line of the clay using any other shape, you will have to be carfull to keep same angle when dragging your tool over the clay or else you will get waves. Find a shpere object you can use it is best.

Now once you have dragged the radius tool over the clay, it will leave a line of clay on each side of the radius. You will have to use something to remove these 2 lines of excess clay without touching the actual clay radius. It Takes a slow steady hand for this step. If you mess the radius clay up no big deal add a little clay and repeat.

Your mold is now complete and ready to build a hatch.


Please come back soon to view rest of tutorial with more pictures. If something doesn't make sense leave a comment below. If you want some one on one support, you will have to join our members only forum at

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Martin Roy

Fiberglass.Website Admin