Concrete Planters

By Sean Michael Ragan
Category: Home, Gardening
Time Required: 1 week
Difficulty: Moderate

The idea here is to use a simple, inexpensive concrete mixture to cast decorative containers using common trash items as sacrificial mold elements. Styrofoam packing inserts, in particular, are available in an endless variety of shapes; the trick is to cultivate an eye for the negative spaces that are molded into these inserts, and set aside the interesting ones to use as outer forms. Inner forms, obviously, should be simpler, because the inside of the pot is not going to be visible.

Steps

Step #1: Gather the mold elements.

I used a styrofoam block I found discarded in a hallway in the UT chemistry department as an outer mold. It contains four identical cylindrical recesses and was originally used to package 4L glass solvent bottles.
The inner forms are nesting polyethylene tubs of the type provided at many grocery stores to package bulk dry goods.

Conclusion

If you have to use a dyed towel, don't despair. Any color that bleeds onto the concrete is fairly easily removed using bleach and a stiff plastic brush.

If you're making a larger piece, you might consider adding some kind of reinforcement to the concrete mixture. This could be a wire mesh pre-form, or stiffening elements that are inserted after the bottom layer is tamped, but before the walls are packed down. It might also be possible to add fibrous material to the bulk concrete mix to improve its tensile strength, but I haven't actually done any experiments to that end as of yet.

There are lots of different concrete mixtures out there, and you should feel free to experiment with other aggregates, even unusual or novel ones. I've made a couple of pots using vermiculite in place of sand in this recipe, which results in a finer, smoother surface texture.

Be careful with this process--once you start seeing discarded styrofoam as a source of inspiration, you may find it piling up faster than you can churn out the pots!