black marks on patio

susananwms

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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susananwms

Thanks for that I will get some today

plant pauper

Freddies Dad said:

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.8

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

Kitty 2

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 Humby

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 2

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😁.

susananwms

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

susananwms

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?