Limestone, Sandstone and Granite are very porous in nature. They typically require specialized cleaning chemicals for effective removal of surface contaminants such as pollution, dirt, mold and/or mildew or rust. Care must be taken to apply the proper cleaner, for the proper amount of “dwell” time, then rinsing with the appropriate amount of rinse pressure.
I am frequently asked how to tell the difference between limestone and sandstone. The easiest way to determine this is to look very closely at the surface. If you see very small, closely compacted seashells/ crustacean shells, this tells you that the stone is limestone. They can be so small (less than 1/4 to 1/2 millimeter) that it may be difficult to determine that it is shells. Or, it can be very plainly obvious because they are so large (maybe 1 to 3 millimeters) in size.