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Enginursday: The Look - the Feel - of Concrete

Inspired to try something new for International Week of Making, Mary mixed and poured concrete over electronics in her office.

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In honor of National Week of Making, I wanted to try something new. Something a little more civil if you know what I mean.

I spent about a week mixing various bags of concrete and cement in search of the perfect pourable consistency, strength and smooth finish in which to encase some electronics projects. My favorite mixture is two pounds of Rapid Set® Cement All® with ¾ cup of water. I mixed the cement in a 1-liter plastic measuring cup with a pour spout and used a set of tiny spatulas to spread and smooth. This bag will make hundreds of projects, which means the cost of an individual project enclosure is at most a few cents.

I found a generic plastic wrap and tape works best to protect the circuit from possible water damage. The concrete clock only had electrical tape over the soldered connections between each WS281T breakout, which worked well.

What I did not expect to happen:

  • The electronics to work after the cement cured — every time
  • Feldi to rub the final projects on her face — it’s that smooth

Tips for your projects:

  • Buy Rapid Set cement or countertop concrete so your waterproofed projects are exposed to water for the shortest amount of time and have no aggregate material — or the least amount possible.
  • Use plastic molds for resin, or silicone baking molds. The projects where I used cardboard cutouts — like Pinterest told me to — gave the worst results (see the first two projects).
  • Have your project completely ready, troubleshot, waterproofed and tested again before mixing the cement. This stuff cures in 15 minutes — or less for smaller, thinner projects.
  • Double-sided sticky tape is a great way to add cutouts for LEDS, switches and an opening for wires.


  • Once your project is in, forget trying to troubleshoot.
  • It takes awhile to get a good pouring technique and think of circuits in terms of negative space within a mold.

Now I’ve got about 51 pounds of cement left to play with — any suggestions?

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