I don’t know of any reason that you couldn’t paint over this product. The only problem I visualize would be that the location is one which probably has soil and grease splatters that might make it more difficult for paint to adhere properly. I would suggest that you just clean the surface as well as possible – perhaps using a stiff brush and a de-greaser. A coat of primer and one or two top coats should finish the project. You may want to roll the finish with a deep nap roller to get between the “mortar”.