Crayon marks are commonly found on chalkboards of all shapes and sizes. Young children and toddlers do not realize that they do not come off as easily as chalk. They just want to draw pictures. Soap, water and a rag will not solve the problem. A common non-abrasive substance and a little elbow grease is usually all that you need to get rid of the streaks. Use these easy ways to remove them, and restore your blackboard to its former condition. Once the mess is gone, keep crayons out of reach. Small children might not stop with chalkboards. They have been known to color on the walls, floors, furniture and other hard surfaces instead of paper.
Create a Paste with Baking Soda and Water
To remove crayon marks from a chalkboard, do not use cleanser or any other abrasive cleaner. Rough sponges can also damage the finish. Make a simple paste with baking soda and water. It should have the consistency of icing. Apply it to a soft clean rag, and gently rub away the crayon marks. Wipe away the baking soda with a clean rag and clear water. The streaks should come right off, and without removing the surface. If they do not come off, try the next option. It will work to get rid of the stubborn waxy stains.
Try a Mr. Clean Magic Eraser
When baking soda paste does not work to remove crayon marks on a chalkboard, use a Mr. Clean Magic Eraser or a generic version of a similar product. I have used both, and they really do work as promised. Follow the directions on the package for best results, and only rub the areas with crayon marks to avoid causing damage. Also, do not press too hard. It is not necessary to apply a lot of pressure while cleaning with a Mr. Clean Magic Eraser or a similar sponge of a different brand. It will work like magic, and lots of elbow grease is not required to remove tough stains.
Does the Board Need to Be Repainted?
If you are able to remove all of the crayon marks but are left with a mottled surface, consider repainting the chalkboard. After boards are wiped many times, they eventually need to be resurfaced anyway. If it is a vintage board or would cost a considerable amount of money to replace, it is probably worth the expense. Shop for chalkboard paint at a local home improvement store. Most popular discount stores that sell paint also carry it, and the color choices are not limited to black or green. With a new coat of paint, it can look brand new and provide a solid background for messages that are written in chalk.
Source: Advanced Crafting and Cleaning Experience