Cleaning Yorkstone

[MasterBlaster]

Hi new to this so 'point' out any mistakes....does anyone have any info on cleaning yorkstone? I am using 200bar pressure washer but unless I stand for 10 mins per flag I cant get this black stuff off, and it dosnt go entirely. Think it is mould is there a treatment for it. Am aiming to start up a professional cleaning company so would be very gratefull of any advice...as I am a bit green! many thanks. Mike

[84-1093879891]

The 'black stuff' is probably lichen, and it's notoriously difficult to shift.

Power washing is the safest and surest method. but with some types of stone and some types of lichen, using a few drops of acid or Jeyes Fluid can help loosen its grip. However, you have to be very, very careful with the acid, as it can damage the stone itself, in some cases.

You're much better off relying on the power washer backed up with a scraper and a wire brush.

[MasterBlaster]

Thanks for the reply. Yes, I guess it might be lichen. Have tried a 200bar pressure washer and after 3 to 4 minutes per 4" sq it reduces the stain to something acceptable. Any idea on companies I can contact for chemical solutions? When I have given the stone a clean with the jet wash some staining remains, am I correct in thinking that this is either staining or the roots of the lichen itself....

[84-1093879891]

I don't know of any guaranteed chemical solutions for lichens. As I said, acid does kill them, but because of the way they grow, even when dead they cling to the surface of the substrate with incredible tenacity.

The marks left after removal are partly the roots/holdfasts of the lichen, but also, because of the way lichens live, it is partly chemically-altered stone/concrete, and there's nothing much you can do about it, other than leave it to the weather for a few years.

[MasterBlaster]

Many thanks for your advice and hats off to you for such an informative website, glad I was told about it!

Going to chance my arm here but doing the work I do the next thing a patio needs after I have cleaned it is pointing, would this be a good place to find someone who could do this kind of work?

Idealy this would suit a retired person with good experience. For example I cleaned a very nice and much loved slate patio/terrace the other day and it needs some tlc to bring it up to scratch again, if you or anyone has any thoughts...

And thanks again for your advice.

[84-1093879891]

You can ask, but I'm not sure many flaggers are all that keen on pointing as a sideline.

It's be helpful if you gave some sort of indication as to the area you work.

[71-1093879301]

I'm pleased to hear that other people suffer from black mould on yorkstone paving - I thought it was me. There must be a chemical out there that removes it other than acids. The only success I have found is my wife's steam cleaner when she's out plus rotary wire brush followed by jet cleaner. This is bloody hard work and stopping me sailing!
Please help me I don't want to do any more.
Interestingly it does not appear under the timber pergola - maybe something to do with the preservatives in the wood?

[danensis]

York stone goes black in the atmosphere. When they built the Elland by-pass they cut through the side of the hill, and there was all this lovely honey-coloured stone. I was up there last week, and its all gone black.

I remember a few years ago there was a fad for sandblasting the stone houses around Hebden Bridge. Within a few years they'd all turned black again. Its not atmospheric pollution, its just the normal action of the air on the stone.

[alan ditchfield]

Has anyone tried sealing after cleaning to see if this stops the staining coming back in the near future i am sure it would help, if so what did you use and what was the outcome. I have done this with the more porous indian sandstone and it has very impressive results. Alan