What's the best way to clean chalkboard paint walls?

I've used a rag with water, but it smears EVERYWHERE. I'm thinking next time I'll try a microfiber cloth if there isn't any better ideas.What's the best way to clean chalkboard paint walls?
Why not just repaint it with chalkboard paint?What's the best way to clean chalkboard paint walls?
Chalkboard paint is made with slate and must have a new coat of chalk put on after it is cleaned. This is done by using a piece of chalk sideways and going over the entire surface. Then erasing it with the eraser. So much for those clean walls huh!
I think I remember my teachers cleaning them with good ole soap and water. That was a while ago though.