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Circluar blotches on sandstone


I've been searching and so far found no answers.  Our sandstone cills appear to be getting circular spots across them, would anyone know what is causing it? Or if it's possible to treat it? Potentially iron reduction spots, but that's about as far as I can see.

Thanks for your help.


  • LynLyn DevonPosts: 21,143
    How long have the sills been there, could be lichen.  We see very similar on headstones, especially sandstone which is soft and porous. 
    Gardening on the wild, windy west side of Dartmoor. 

  • dom.evesdom.eves Posts: 2
    Hi Lyn,

    Thanks for the reply.

    About four years.  I did try some wet and forget on them which didn't seem to make much difference.  However I have been recomended Lithofin Outdoor Clean to try with the suggestion it could also be lichen.

    I will try that and see how I get on.

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