Plaster Stains in Patio

Floopy2009

Noticed some multifinish plaster mark's on patio and drive. The traders look like they have tried to clean it off but made it worse smudge Mark's  Hasn't rained yet but whats the best hack to sort this out from experience 

Cheers 

CliveOfIndia

The first thing I'd try is going over it with a jet-washer, if you have one.  Failing that, get it nice and wet and give it a good scrub with a stiff brush.

A solution of vinegar may help - vinegar is acidic and plaster is alkaline, so that would probably help to dissolve the stains.  Any old vinegar will do - just get the cheapest own-brand stuff from Aldi/Lidl/wherever.

Edit to add: You can get cement/brick cleaner from any of the DIY/hardware shops, which again is acid (Hydrochloric usually, I think ?).  But that's probably a bit overkill for plaster marks, which should come off pretty easily.

stuart45

Check what your slabs are. Acid will attack limestone. It also breaks down Portland cement products, so concrete slabs can get stained. 
Lithofin power wash is another option.