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.   
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  • susananwmssusananwms Posts: 38
    Thanks for that I will get some today
  • plant pauperplant pauper Posts: 6,236
    White vinegar works a treat. I used it to remove some rust and other stains and it worked. Leave on for 30mins then wash off with soapy water and a stiff brush. Caveat: the spots and black marks may be the natural surface as the coloured stone has worn away (esp with the pressure washer). I would stay clear of bleach as it is corrosive.
    So's vinegar...
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  • Pete.8Pete.8 Billericay, EssexPosts: 4,652
    I think if it were me, I'd call the supplier and ask their advice.
    You don't want to make matters worse.
    There are specialized sandstone cleaning products.

    There's a lot of info here-
    http://www.pavingexpert.com/maintain_02.htm#acid
    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • Kitty 2Kitty 2 ManchesterPosts: 5,090
    I'm wondering if the "black marks" are actually lichen growths?  When I jetwash the patio the muck and algae blasts off with no problem, but the lichen spots stay put.

    Have you got a photo @susananwms ?
  • Dave HumbyDave Humby Posts: 886
    Kitty 2 said:
    I'm wondering if the "black marks" are actually lichen growths?  When I jetwash the patio the muck and algae blasts off with no problem, but the lichen spots stay put.

    Have you got a photo @susananwms ?
    I think that's more likely rather than rust. The lichen is VERY difficult to remove.

    Some good info here:

    http://www.pavingexpert.com/maintain_03.htm 

  • Kitty 2Kitty 2 ManchesterPosts: 5,090
    Interesting article link Dave👍
    I have to admit to not being bothered about eradicating the lichen off my paving, so leave it be.

    Not much help to susananwms, sorry. But it is a sign of clean air supposedly😁.
  • susananwmssusananwms Posts: 38
    Hi all, yes i have been told that it is Lichen.  All the green mould and dirt washed off but has left black spots, more on some of the stones than others.  I do not want to use the sealer until they I get them off.  have tried white vinegar but it did not remove them
  • susananwmssusananwms Posts: 38
    Dave Humby thanks for your link.  According to that i should try Calcium Hypochlorite or Ammonium Hydroxide.  Has anyone had experience with these products and is one better than the other or easier to use?
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