Honestly unless it’s for aethetics, paint isn’t even necessary especially for a curb. That being said I just redid a ledge at my diy and painted it then clear coated it and it turned out amazing. But I only painted the sides (granite slabs on top of blocks) I did grind the granite smooth and put several coats of clear on it skated the first time today and skated amazing and didn’t even need to wax it. The trick I’ve found is get the surface smooth, grinder or rub brick, get all the dust off and put several liberal coats of clear allowing plenty of dry time.