Inspiration:

Image Credit: Chiether under CC-BY SA 3.0 (Resized)

Tetrapods are large concrete structures that are used around the world to break up wave action and absorb the ocean's eroding energy. This miniature tetrapod was made from small plastic cups, tacked and taped together with hot glue.

STEP 1: Make the Form

Drill or cut a hole in the bottom of one cup, this will be the hole to fill with the mix. Tack the 4 cups together with hot glue. Arrange them as seen in the picture, or in any way you like.

Tape over the gaps with clear packing tape. Wrapping the tape around the cups will help hold them together.

STEP 2: Mix and Fill

Mix ShapeCrete to a Castable Consistency and fill the form in stages. Gently vibrate the form to minimize air bubbles. Filling it a little bit at a time will help the mix flow into the cups without trapping air in the corners. When the form has been filled, smooth the top flat.

STEP 3: Cover and Cure

Cover the piece with plastic and let it cure for at least 24 hours.

STEP 4: Break Away Plastic

After the piece has cured, remove the form by first peeling the tape off. Gently break the plastic away and remove the cups. It might help to slice the plastic with a utility knife or razor blade and then use needle nose pliers to break the cups off.

Rough edges can be sanded down with diamond hand pads, sandpaper, or files.

For another fun project, check out the Door Stop: