Does lichen damage my soft top roof?
Quick answer: Lichen doesn't eat the fabric itself; the soft top is made of tough synthetic fibres. The damage comes from the dirt and grit the lichen is feeding on and holding in place. Left long enough it also stains the fibres and can abrade the stitching. Remove it gently with a dedicated hood cleaner and a stiff brush, rinse, repeat, then re-proof. Never use a pressure washer.
Lichen on a cabriolet roof looks alarming, and most owners assume the little green-grey crust is eating into the fabric. It usually isn't. The fabric underneath is normally sound. The real harm happens beneath the lichen, and in the panic to get rid of it.
What lichen actually is, and why it picked your roof
Lichen isn't a single plant. It's a partnership between a fungus and an alga living together as one organism, and it will colonise almost any surface that stays damp and undisturbed long enough: gravestones, garden walls, north-facing fence panels, and the rear quarter of a folded convertible hood that sits in the shade. It doesn't need soil. It needs moisture, a bit of light, and something to anchor to.
A car that's driven daily rarely grows lichen, because the roof flexes, dries in the airflow and gets cleaned now and then. The roofs we see it on are the ones that sit still: a second car, a summer-only convertible put away for winter, or a hood parked under a tree where it's permanently shaded and dripped on. If lichen has taken hold, the roof has been damp and untouched for months.
Why lichen doesn't harm the fabric directly
A soft top is woven from tough synthetic fibres, usually an acrylic or polyester cloth with a backing layer. Lichen weaves itself between those fibres, which is what makes it such a pain to remove, but it doesn't digest them. What it's actually feeding on is the organic matter trapped in the weave: dust, pollen, tree sap, bird droppings and general airborne debris. That film of grime is the food source.
So the lichen itself isn't the disease. It's a symptom. If there's enough trapped dirt on a roof to grow a living organism, there's more than enough to be doing quiet damage already. The lichen is just the visible flag that says the fabric has been neglected.
The real damage is underneath
The dirt and grit the lichen is sitting on is abrasive. Every time the hood folds down and comes back up, that grit grinds against the fibres and against itself, and it cuts wear marks that are permanent. The mat of lichen makes it worse: it keeps the grit pressed into the weave and stops normal rain from rinsing it away, so the abrasion just keeps happening in the same spots.
Lichen also holds moisture against the roof like a damp sponge. That accelerates the breakdown of the waterproofing layer. Once the proofing is gone the fabric wets through instead of beading, stays damp for longer, and that damp surface is exactly what more algae and moss want. It becomes a loop: damp feeds growth, growth holds damp.
The other quiet casualty is the stitching. The seams on a hood are where the panels join and where the fabric is under the most tension, and a lichen colony that's sat on a seam for a season abrades the thread as well as the cloth. Frayed stitching is a far bigger job than a stained panel, because it's structural; once a seam lets go the roof has to come off the frame to be re-sewn.
The mistakes that turn a cleaning job into a re-trim
Tom, our operations manager, has a standing line about lichen jobs: most of the damage we're asked to fix wasn't done by the lichen, it was done by the owner the weekend before they called us. There are two classic ways to wreck a roof while trying to save it.
The first is the pressure washer. You should never put a pressure washer near a soft top. The pressure it takes to blast lichen out of a weave is well past the pressure that cuts the fabric, drives water through the backing and chews the stitching out of the seams. We've had a hood come in with a clean lichen-shaped patch surrounded by a halo of furred-up, water-logged fabric where the lance lingered; the lichen went, and so did the proofing and the surface nap with it.
The second is harsh chemistry. Thick bleaches, patio cleaners, oven cleaner and solvents will all lift lichen, and they'll all do collateral damage on the way. They bleach the colour out of the cloth in pale patches, perish the rubber seals around the hood, and stain the paint and trim wherever they run off and dry. A very dilute, gentle bleach such as Milton fluid can be used carefully on the fabric itself to knock back staining, but it has to be kept off the trim, glass and paint, and rinsed out thoroughly. The household-strength stuff under the sink is not in that category.
The right way to get it off
Lichen removal is slow, repetitive work, and there's no product that does it in one hit. The honest sequence looks like this:
- Brush off the loose surface growth dry, before any water goes near it, so you're not just spreading mush around.
- Wet the panel and soak it with a dedicated hood cleaner, then leave it to dwell so the chemistry can soften the roots in the weave.
- Agitate with a stiff brush, working the fabric rather than scrubbing one spot raw, and rinse with a normal hose or watering can.
- Repeat the soak-agitate-rinse cycle, usually two or three times, because lichen comes off in layers, not all at once.
Once the fabric is genuinely clean and has dried right through, which can take a warm day with the hood up, it has to be re-proofed. The roof has lost its waterproofing twice over by this point: once to the lichen and once to the cleaning. A proper fabric weatherproofer does two jobs at once. It lays down a hydrophobic film so the cloth beads and sheds water instead of soaking it up, and many carry biocides that slow regrowth, so the colony doesn't simply re-establish on the same damp panel.
One thing that is never a shortcut for any of this: putting the car through an automated car wash. The brushes won't reach into the weave, and car-wash chemistry is formulated for paint, so it'll happily strip what little proofing is left without touching the lichen. You come out the far side with a wetter roof and the same problem.
Stopping it coming back
Lichen is a parking problem before it's a cleaning problem. The roofs that grow it are the ones left damp and shaded; the cure and the prevention are the same thing pointed in different directions. Keep the hood reasonably clean so there's no organic film for anything to feed on, keep it proofed so water beads off instead of sitting in the weave, and where you can, don't leave a convertible parked under a tree or against a north wall for months on end. A roof that dries out between rain showers doesn't give lichen the standing damp it needs to take hold in the first place.
If a roof has already lost panels of colour to staining, or the stitching has started to fray, that's past the point a clean-and-proof will rescue and into repair territory; but a roof that's simply crusted with lichen on sound fabric is almost always recoverable with patience and the right products.