Can I use a pressure washer to clean my soft top?
Quick answer: We advise against it. A pressure washer can mark or even tear soft-top fabric. If you must use one, keep the lance at least 20 inches away on the gentlest setting. Self-service units at a forecourt are safer than a domestic high-pressure washer. The proper way to clean a hood is a stiff brush with dedicated cleaner, then a thorough rinse from a standard hose nozzle.
A pressure washer can help you clean a convertible roof, but the margin between clean and damaged is narrow. By the time the jet is close enough to shift roof green, it is close enough to bruise the fabric.
What a pressure washer does to a hood
Many pressure washers push water out hard enough to rip through a cabriolet hood. More commonly, the jet roughs up the surface and leaves zig-zag marks across the fabric. Both outcomes strip the weatherproofing and open the way to stains and, at worst, tears.
Domestic vs industrial pressure washers
Not all pressure washers behave the same. The domestic type most people keep at home runs on very high pressure and is the most likely to do damage. Industrial units of the sort you find at self-service car washes often run at lower pressure with a much higher volume of water. They are safer, but still worth approaching with caution.
If you have enough pressure to actually clean off lichen, you have enough pressure to damage the roof.
This is what it looks like in practice on an Audi A3 Cabriolet. The owner had been trying to shift green growth. The zig-zag pattern is the jet path through the fabric.
The safe way to clean a soft-top
The only reliable method is to scrub the hood with a brush and dedicated cleaner, then rinse the dirt off. Getting the roof properly clean needs a lot of rinsing, and a bit of pressure behind the water helps, but a standard hose nozzle does the job without risk.
If you do use a pressure washer, hold it at least twenty inches off the hood. The temptation is always to close that gap to save work. You may think the jet is lifting dirt without marking the fabric, but you won't see the damage until the hood has dried out.
Keep the jet away from seams, rubber edges and the rear window. Those are the points that fail first.
General maintenance
The best way to avoid a green roof is to clean the car regularly. If you already wash your own car and you already own a pressure washer, telling you not to use it is unrealistic. Keep it a good distance back from the hood, work on the gentlest setting, and finish with a thorough rinse from a plain hose. The same caution applies to automated car washes -- the bristle rollers and chemistry at a forecourt are not designed for fabric hoods.