Introduction: Concrete Mini Tetrapods

Picture of Concrete Mini Tetrapods

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

Picture of 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

Picture of 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

Picture of 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

Picture of 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.


ilpug (author)2015-07-18

Could you do this with normal bagged concrete mix? What is it about ShapeCrete that makes it preferable for this application?

ShapeCrete Mix (author)ilpug2015-07-20

ShapeCrete doesn't have large rock aggregate, just different sizes
of sand, so it's a finer mix. It also gets harder much more quickly than
traditional concrete, so it can be removed from the form after a day.

only problem with using a normal bagged mix is that the largest rock
aggregate is usually about 3/8" in size, and the opening to fill through
is only about 3/4".

If using regular concrete, buy a 5000 psi.
bagged concrete mix and then remove the larger rocks. Fill the form
gradually and vibrate it a lot to help consolidate the mix and minimize
air bubbles. Then leave the piece to cure for 5+ days and you will still
get good results.

ilpug (author)ShapeCrete Mix2015-07-21

Okay, cool! That's a lot of useful advice.

mapski99 (author)2015-07-21

Very cool. You could even lay the cable inside the form, through a bottom cup, with the iphone (or android) port on the top - awesome phone charging station!

ktang1 (author)2015-07-20

How do you do the color? Thanks!

ShapeCrete Mix (author)ktang12015-07-20

Colored pigment is added to the dry mix. Check out this link for more detailed instructions:

There are a lot of pigments that will work, but the blue used here is Tahoe SmartColor:

Ashton c (author)2015-07-17

Finally a holder for donuts

KataNinja (author)Ashton c2015-07-20

You just made me smile kind sir. I tip my hat to you.

natrinicle (author)2015-07-17

I spent entirely too long attempting to figure out what the usb cable was for... Awesome paper weight design though!

Ric Malandrino (author)2015-07-17

they use this to protect an airport in Korea I think. but I wouldn't use that to hold earbuds. I have REALLY nice designs on ear bud holders but the design it secret at the moment because of producing them and brining them to the market. I'm only 13. but I like the cment part of it

seamster (author)2015-07-17

Neat idea! The shape looks like it would be a great base for a lamp, or charging station. I like this!

ShapeCrete Mix (author)seamster2015-07-17

Yes, exactly!

I want to use dixie / styrofoam cups to cast a larger base for a floor lamp.

seamster (author)ShapeCrete Mix2015-07-17

That would be really cool!

About This Instructable




Bio: ShapeCrete is a just-add-water-and-use, shape-able concrete that can be poured, rolled, pushed or molded in an infinite array of custom concrete designs. ShapeCrete is rolling ... More »
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