I have a 4ft x 20ft smooth concrete sidewalk with a 4ft overhang roof over it with porch and floor paint on it. What is the best way to prep this sidewalk before I install my frost free tiles. I already know how to tile but it's the prep work of the painted concrete I am not sure about. I know the very best way to take care of this is to grind all the paint off but can you just scuff up the paint and do my thing or???