With previous projects I used wood and wood glue to build the structure. At the end the structure was painted with epoxy to make it watertight.

For the next fish feeder I needed a casing that was also waterproof. The casing should protect the nice machinery inside. To see the nice machinery, the side walls should be transparent. Because epoxy is transparent, the side walls are made of epoxy.

Step 1: Partslist

Most important when working with epoxy is carefully reading instructions and safety precautions!

The favorite epoxy I use is suitable for fish tanks from Mr.Boat, see link https://www.mrboat.nl/mrboat-epoxy/. It is strong, transparent, not smelly and easy to mix.

To make the paper non sticking to epoxy a laminating pouch or packing tape can be used. To make wooden parts non sticking only packing tape can be used. The laminating pouch and packing tape must be made of PP or PE (these plastic are difficult to glue). Please verify first if your laminating pouch and packing tape is non sticking to epoxy by:

put a droplet on the plastic,
wait for 24 hours for the epoxy to cure,
try to peel of the epoxy.

If the epoxy comes off easily and in one piece, then you have the right tape.

Parts list:

Epoxy (Mr.Boat)
Packing tape (Tesa, 3m or similar)
Cardboard
Glue
Balsa wood
Wood glue

Step 2: Outside Mold

The outside mold is made from cardboard, reinforced with horizontal ribs.

Draw on the cardboard the bottom and sidewalls of your casing.
Add an extra centimeter to the sidewalls (filling with epoxy will make the walls bulge and epoxy will shrink during curing).
Laminate the cardboard.
Cutout the unneeded parts.
Close the open corners with packing tape.
Make the ribs around the casing and fix them with packing tape.

Step 3: Inside Mold

The walls of the inside mold should be stiff, so I made them out of wood (balsa). To avoid bulging, space can be filled with cards. Sliding a card in between pushes the walls outwards.

To position the inside mold correctly to the outside mold, a wooden bottom and L-profiles at the corners are used.

Draw the inner walls, add an extra centimeter to the sidewalls.
Cut the inner walls.
Position the wooden floor and L-profiles in the outer mold.
Position the inner walls in the outer mold.
Glue the inner mold.
Push the inner wall outward by pushing in cards.
Wait until the glue is settled.
Laminate the inner mold with packing tape.

Step 4: Filling With Epoxy

Most important when working with epoxy is carefully reading instructions and safety precautions!

Determine the volume you need. Mix the epoxy by weight. Take in account the minimal amount of epoxy of 90grams. Take in account bulging of your molds and shrinking when curing of the epoxy.

Follow the instructions of the supplier of the epoxy. See:

- http://www.mrboat.eu/manual-epoxy/

- http://www.mrboat.eu/handleiding-epoxy/

Measure the resin and cure agent in separate cups. Make sure everything is ready. After mixing the resin and agent together there is only a ~30minutes window before the epoxy starts to gel.

Fill the outer mold with a thick layer of epoxy.
Insert the wooden floor. Start by pushing it gently into the epoxy at one side. Slowly let it slide in. Avoid air bubbles to trapped in the epoxy.
Slide in the U-profiles the corners
Move the mold to an angle and let the epoxy flow to the corner.
Slide in the inner mold. Start by pushing it gently into the epoxy at one side. Slowly let it slide in. Avoid air bubbles to trapped in the epoxy.
Fill in the inner mold with cards to avoid bulging
Let the epoxy cure for 24 hours.

Advice: Garbage bags are usually made of PE. Use a garbage bag to cover your floor and/or workbench to protect it against epoxy.

Step 5: The Result

After curing the epoxy it is ready to remove the molds. Be carefully when removing the molds. When using sharp instruments you can easily scratch the surface of the epoxy.