Help with Tough Lichen on Sandstone

[Alfster]

Hi,

Trying to remove lichen black spots from sandstone patio. Tried using sodium hyperchlorite (15%) neat with no dilution and to be fair it has worked extremely well as you can see from the before picture. However, there are areas that just literally do nothing even when you put undiluted sodium hypochlorite on them and scrub hard (and repeat several times!). The picture with the sodium hyperchlorite bottle in the background has some weird black leaf looking thing on it! On this picture since it's a close up you can see that there are quite a few black spots left mainly around the joints/edges of the slabs. Any ideas or is this as good as it's going to get?

Thanks

 

[Stanley services]

That’s more than likely as good as you’re going to get, looks great though. it looks like the remainder lies in small pits on the flags. Perhaps try soaking in a strong anti fungicide solution for a few hours and finishing with a jet wash, (with goggles). Brick acid may well stain so don’t use that.