Issues · 8 min read
Lichen on north-facing Cobham roofs — why it thrives and how to remove it
The flat grey and mustard-yellow circles are lichen — a fungus-algae hybrid that bonds hard to tile. Here is how to remove it without damaging the surface.
Why north pitches suffer most
North-facing pitches receive a fraction of the UV that south pitches do. Combined with the dense tree cover around Fairmile, Sandy Lane and Oxshott, they stay damp for hours after rain — ideal conditions for lichen to establish.
Why scraping alone does not work
Lichen bonds chemically to the tile surface. Mechanical scraping removes the visible body but leaves the holdfast — which regrows within a season. Only a biocide-led soft wash kills the holdfast fully.
Our lichen removal protocol
A stronger DEFRA-approved biocide dwell (up to 45 minutes) followed by a very light rinse, and where possible a follow-up biocide application 6 weeks later once weathering has lifted the dead residue.
Preventing recolonisation
Zinc ridge strips slow lichen dramatically on the exposed pitches below. Where crown-tree cover is unavoidable, we recommend a biocide top-up every 18–24 months to prevent visible establishment.
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