If a power washer is used with care it will take off any lichen in large smooth areas but I wouldn't advise using a power washer on any joints. When we lived in France we were advised to use a product called "anti-mousse" once a year on all the white walls of our house to prevent lichen stains. It didn't harm our upvc windows nor the walls but it did work. You spray it on like a car wax at low pressure, then hose it off at higher pressure. It's cheap (in France) and available from places like Mr Bricolage. I haven't seen it in this country as such but feel sure there will be a version of it at B & Q etc. On own van I am getting small lichen growths in joints etc but find the Autoglym body conditioner rubbed in neat and then washed off gets rid of it.
Surprised at lack of comment on caravan industry economic issues.
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