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 by casting ShapeCrete in small plastic cups that were tacked together with hot glue.

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

Materials + Supplies:

Plastic Shot Glasses from the Dollar Store
ShapeCrete or Fine Concrete Mix
Hot Glue Gun
Clear Packing Tape
Utility Knife
Sandpaper

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 pictures, 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 is completely full, smooth the top flat.

Cover the piece with plastic and let it cure for 24 hours, or much longer if you're using a different type of concrete mix.

Step 3: 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.

Step 4: The Finished Piece

Tetrapods are designed to nest together, so the more you make, the more fun they'll be.

As a desk object, it's useful for holding small charging chords. It may also be useful for holding hair ties, jewelry, bracelets, donuts, stuff like that.