White & Black Lichen on Patio Slabs

Why lichen bonds so firmly to stone

Lichen, whether white, black, yellow or grey, anchors itself into the microscopic pores of natural stone, concrete and even some porcelain paving using root-like structures called rhizines. This isn't surface dirt sitting on top of the slab, it's an organism that's physically grown into the material, which is exactly why standard cleaning methods that work fine on general grime and algae so often fail to fully remove it.

Older, more established lichen colonies have had years to deepen this anchoring, which is part of why patios that haven't been cleaned in a long time often show lichen that's noticeably more stubborn than a colony that's only a season or two old.

An honest treatment timeline

Professional lichen treatment uses a biocide applied directly to affected areas, left to dwell for a period, often several days up to a couple of weeks depending on the product and how established the lichen is, before the dead organism is washed or gently brushed away. Even after that dwell period, some residual colour or texture can remain visible until subsequent rain and natural weathering finish lifting the dead material over the following weeks.

For heavy, long-established lichen, a single treatment sometimes isn't enough, and a second application some weeks later is a realistic possibility worth budgeting time for rather than expecting complete removal from one visit.

Why pressure alone won't finish the job

Jet washing can lift the surface layer of a lichen patch and make it look temporarily better, but without a biocide treatment killing the rhizine root structure first, lichen typically regrows in the same spots within a season, since the anchoring structure that survived the pressure wash simply regenerates visible growth from what's still embedded in the stone.

This is the honest reason a jet-wash-only patio clean often disappoints on lichen specifically, even when it does a genuinely good job on general dirt, moss and algae elsewhere on the same patio.

It's also worth noting that pressure applied specifically to lift stubborn lichen, rather than a gentle general clean, risks etching softer natural stone like sandstone, so the very approach some people reach for to shift lichen faster can end up marking the paving in a way that's harder to fix than the lichen ever was.