Algae

Algae can grow where dirt collects on your roof, especially when weatherproofing has worn off and the roof is allowed to remain damp.

On some cars, the tape around the seams and edges may contain natural fibres and is particularly prone to algae (as shown in the photo), from there, algae can grow very rapidly causing much of the car's roof to turn green in a short space of time.

Technically, this powdery greening is made up of cyanobacteria and fungus, making it a lichen. However, it is generally referred to by people as 'algae' or 'roof green'.

What it means

Algae is the thin green film you see on cars that have been left damp and dirty, especially under trees or on north-facing drives. On vehicles it tends to appear on fabric and mohair soft tops, window rubbers, gutter trims, wiper arms and other textured areas that stay wet longer than flat paintwork. It often feels slightly slimy when wet and can leave streaks or patches that make roofs and trims look dull and dirty.

Why it matters

• Lets the car down visually: Even if the paint and interior are reasonable, green film on the roof and rubbers makes the whole car look neglected.
• Holds moisture and dirt: Algae traps water and grime against fabrics, rubbers and seams, which is not ideal for stitching, membranes or paint edges.
• First stage before worse growth: If left, light algae growth can progress to thicker moss and even lichen, which are harder to remove and more deeply attached.
• Can stain and mark surfaces: Long term algae, especially on pale roofs and trims, can leave shadowing or stains that need more intensive cleaning to reduce.

Where you’ll see it

You will see algae most often on soft tops and around glass and roof edges. Common areas include the top and shoulders of fabric roofs, the base of window rubbers, inside roof gutters, around tailgate channels and along trim joins. Inspection and detailing reports may note algae on soft top and rubbers, green algae build-up in gutters or algae staining on roof edges.

Context

Algae is part of the same family of biological contamination as moss, lichen and mould, but it usually appears first as a relatively flat, slimy film. On soft tops it is often the layer you see before moss clumps form. Proper treatment involves pre-soaking with suitable cleaners, gentle but thorough agitation and controlled rinsing, followed by appropriate protection such as fabric roof proofer or trim dressing. On paintwork, careful decontamination and protection help stop algae getting a foothold again. Because algae likes damp, shaded areas, good drainage and regular cleaning are just as important as the products used.

Common mistakes

• Blasting algae with very strong TFR or harsh household cleaners, which can bleach or weaken fabrics, rubbers and plastics.
• Scrubbing aggressively with stiff brushes on soft tops and rubbers, damaging fibres and seals while only partly shifting the algae.
• Assuming a quick wash will cure heavy algae build-up, instead of planning a careful, staged clean followed by the right protection.
• Ignoring early algae growth on roofs and trims until it thickens into moss and lichen, making restoration more difficult and time consuming.

Written by Danny Argent. Last updated 03/12/2025 17:42