Not a horticultural question but still a garden question. I have a patio of indian sandstone which is now quite stained with small black circular discrete marks, almost appearing like a fungus or lichen.The marks are quite random, some stones being affected and others not at all. Despite use of a proprietary patio cleaner and power hosing the stains remain. Have you any suggestions? The run-off is onto grass.Many thanks, Paula
It is difficult to keep sandstone in its original prictine condition. It may fade or exude iron salts on the surface, causing a rusty colouration. Power washing and scrubbing can be carried out.
Patio cleaners are based on a variety of chemicals, either caustic soda or acid. Both of these can be dangerous and may not give good results. Acid can cause more rusty discolouration. Before using any product, test it on an out of the way corner.
Household bleach does quite a good job on algal staining, but may need to be repeated and will definitely have t be used on an ongoing basis, unless the paving is sealed with a sealant. These tend to change the appearance of the stone giving it a darker appearance often and a less natural finish.
No simple solution unfortunately, unless you simply get to like the ageing process!