Mix together the water and plaster until well combined.
Color the mixture with tempera or acrylic paints or food coloring. Using paints will provide a much brighter color. Mix together until the color has evened out.
Pour the mixture into silicone molds or cardboard tubes like the ones leftover from finished toilet paper rolls. I used both heart shaped ones (which are great for little hands) and tall thin molds meant for making ice cubes for bottles. They both worked really well as chalk molds.
Allow the plaster to dry completely. When I used a lighter plaster, it took a couple of days to harden and dry out enough to take the chalk out of the molds easily.
Unmold and have fun writing on the sidewalk outside.
Recipe printed from Oh, The Things We'll Make! Blog. https://thethingswellmake.com/heart-sidewalk-chalk-valentines-day/