According to Lowe's, chalkboard paint should not be used outdoors. However, flat latex paint can be used in place of chalkboard paint for certain outdoor projects. Flat latex paint is similar to chalkboard paint and can be wiped down easily.
It's typically best to prime all painted surfaces before using flat latex paint. After priming, several coats of latex paint may be needed to achieve the desired result. Exterior chalkboard paint can also be made with a mixture of exterior latex paint and tile grout. Mix 1 cup of latex paint with 2 tablespoons of tile grout, and apply it to a clean surface.