A BMW 3 Series convertible at 52,000 miles -- moss growing, lichen breaking down the fabric at the fold lines. Gary shows the chemical soak and power brush process, explains why the roof can still be saved, and what a new aftermarket roof would cost if it had been left any longer.
This BMW 3 Series convertible has 52,000 miles on it and the roof is covered in moss with lichen starting to break down the fabric. Gary explains what is happening, whether it can be saved, and what the process looks like.
What Happens if You Leave It
Moss and lichen are not just cosmetic. The organisms hold grit and moisture against the fabric, the abrasion works into the weave every time the roof folds, and eventually the stitching starts to perish. The fold lines are always where it starts -- you can see where this one has survived at the folds, but Gary mentions another car coming in the following week where the stitching is already coming apart at exactly those points. That one may be beyond saving.
A new aftermarket soft top, supplied and fitted, runs to around £1,500. And trimming it is not as simple as it sounds -- the roof is not just fabric. Underneath is a neoprene rubber membrane, like a sealed layer under a tent. A hole in that membrane is like a hole in the bottom of a boat. You cannot stitch it back together with a needle and thread on the side of the car.
The Cleaning Process
You cannot go straight in with a brush -- that just drives the grit deeper and wears the fabric faster. The correct sequence is: soak the roof with a chemical that breaks down the organic matter holding the grit in place, leave it to dwell, then power-brush the loosened material out. Gary describes it as replicating what a washing machine does -- agitation after chemical treatment, not abrasion before it. The process runs through a couple of passes until all the dirt is out of the weave.
On this BMW the fabric came up clean. Where the lichen had been sitting longest you can see the fibres are slightly worn, but the roof survived -- still folding cleanly, still structurally sound. Once clean it was given a hydrophobic coating to protect it for the next couple of winters. With that coating in place, water beads off, dirt does not bond to the surface, and the roof stays cleaner for much longer between washes.
If your convertible roof is going green or starting to look tired, the sooner you bring it in the better the result -- and the less likely you are to be looking at a replacement. See our convertible roof cleaning and restoration service.
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