black marks on patio
Have got a big problem with my patio. It is pink coloured sandstone and is only 3 years old. It has cleaned up nicely with a power washer previously but this time I am left with black marks and spots all over it. I have bought some sandstone sealer to treat the tiles with when I can get them clean. I have tried bleach which has removed some of them but most still remain. My patio slopes very slightly so I cannot keep the bleach in place for any length of time. I am really concerned about damaging the stone with so much scrubbing and power washing but do not know what else to do. Any advice at all would be most welcome.