Sidewalk Chalk Mold Project

Sidewalk chalk is a time honored way for children to have fun. While you can buy it at the store, it is also possible to make your own at home for pennies.

Different home school sites (link crafty creations) and craft sites have shown how to make sidewalk chalk. They use toilet paper tubes as the mold.

But in looking at the sidewalk chalk sold at the store, I realized that a 3D printed mold could be used to cast chalk.

Designing the Chalk

TinkerCAD (Link) is my favorite CAD program for quick projects and design work.

I’ll post the full details in my TPT (link to site) for how to design a mold.

To design your own, start with the design you want for your chalk. I wanted mine to not role around, so I used the hexagon basic shape as a foundation. After that I added a parabola cone to the front of the chalk to make the master form.

Finally I added in a logo to make the final chalk shape. With this I could virtually form mold in TinkerCAD.

Forming the Mold

With any mold the draft angle needs to be considered. This will make the difference between the casting sticking inside the mold, or popping free. My first mold had a 90 degree angle, and some of the casting experiments would not release cleanly from those molds.

The second mold design went much better with an obtuse draft angle. This made sure the chalk would release clean from the mold. You can print the mold in any ridged material for this. I used the ugliest pink PLA filament I had to get rid of it. I figured this would get dirty with plaster, so I don’t relay care how it looks. I also printed a couple test molds in TPU. You can play with flexible molds (link cement) but for chalk I found that ridged molds work the best for casting plaster.

Casting the Chalk

This is the messy step in the process. Make sure to do this in a garage or makerspace you can clean up easily.

To prepare the mold, make sure to tape the mold shut with a liberal amount of duct tape (affliliate link) or packing tape (AL). I also gave a quick spray of cooking oil into the mold as a release agent.

For this mix you need 2 parts plaster of Paris (affiliate link) to 1 part water. An easy way to keep the mess down is to mix the two in a disposable sandwich bag. You want the mix to be the consistency of smooth pancake batter. If you want to color your mix I found that powdered tempera paint (AL) mixed 1 part color to 2 parts plaster works great.

You can also use acrylic paint to color the chalk mix, but I found that it takes a couple days for the paint to finish off gassing, so it smelled moldy when the chalk first comes out of the mold.