I laid indian sandstone patio about 8months . In the last month or so i have noticed loads of little black spots appearing in the flags. The flags were laid in concrete. I have read several articles about the porous nature of sandstone which can allow problems to occur with algae and even water however i have not found anything which identifies the problem im having.
Has anyone come across a similiar problem and know of any treatments i can use to remove these blacks spots?
Indian sandstone - Black spots taking over
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Tony McC
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paving_mad
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