Common problem

Crusty lichen on roof tiles and why it is harder to shift than moss

Lichen is the flat, crusty grey, white or orange growth that looks painted onto the tile. It is not moss, it does not lift off in mats, and it takes considerably more patience to deal with.

We see the worst of it on clay peg tiles and older slate in the Chiltern-facing parts of Luton and around the damp valley floors in Hitchin and Shefford.

Ask about lichen treatment 07418 611188

Why it grips so hard

Lichen is a symbiotic organism — fungus and alga together — and the fungal component physically bonds into the surface of the tile. On a porous, weathered clay or concrete tile it is anchored into the material rather than sitting on top of it.

That is why hard scraping does not solve it. Get aggressive enough to lift every trace and you take tile surface with it; leave the anchored material and it regrows from what remains.

The realistic approach

Remove the bulk growth by hand, working along the courses rather than across them.
Treat the whole covering with biocide so what remains anchored in the surface is killed rather than trimmed.
Accept that residual ghosting on very porous tiles weathers off gradually rather than disappearing on the day.
Never use a pressure lance — on lichen-affected clay it removes tile, not just growth.

Where we see it most

Damp, sheltered, chalk and clay locations with clean air. Lichen is famously sensitive to air pollution, so it thrives on rural and semi-rural roofs: the Chiltern edge above Luton and Dunstable, the Hiz valley through Hitchin, the greensand villages around Woburn Sands, and the Ouse valley towards Newport Pagnell.

Our own photographs

Images from Sky Scrapers Ltd work showing the methods described on this page.

a moss-covered pitch photographed part way through hand cleaning, relevant to crusty lichen on roof tiles and why it is harder to shift than moss

a roof slope part cleaned, showing the untouched moss alongside, relevant to crusty lichen on roof tiles and why it is harder to shift than moss

a cleaned pitched roof on a detached house, relevant to crusty lichen on roof tiles and why it is harder to shift than moss

Where this applies locally

Towns where this comes up most often on our patch:

Questions we get asked

Is lichen worse for the roof than moss?

It holds less water than moss, so it does less to block drainage, but it bonds into the tile surface and is much harder to remove cleanly. Structurally moss is the bigger nuisance; visually lichen is the more stubborn.

Why can't you just scrape it all off?

Because the fungal component anchors into the tile. Scraping hard enough to remove every trace removes tile surface as well, which makes the next colonisation faster.

Will the roof be spotless afterwards?

On sound tiles, close to it. On very porous or weathered tiles you may see faint ghosting where the growth was, which weathers off over the following months.

Does lichen mean my air quality is good?

Broadly, yes — lichen is intolerant of heavy air pollution, which is why it is most abundant on rural and semi-rural roofs.

Deal with lichen the slow, correct way

Lichen jobs take longer than moss jobs and we would rather set that expectation before quoting. Send us a close-up photo.