How to remove black spot lichen from a patio (without damaging the stone)

Black spot will not pressure wash off. Here is the method our trade customers use on sandstone and limestone, step by step.

Black spot is a lichen, not dirt. It roots into the top few millimetres of the stone, which is why a pressure washer only removes the surface colour and leaves a grey shadow — or worse, scars the slab.

The reliable approach is chemical. Clean the surface first so the treatment can reach the lichen, apply a dedicated black spot remover at the stated rate, then leave it. Results appear over two to six weeks as the dead lichen weathers away.

Always test a small area first, protect planting with plastic sheeting, and wear the PPE listed on the safety data sheet.