"RedDrawf" <email@example.com> wrote in message
>> > "Peter" <firstname.lastname@example.org> wrote in message
>> > news:rot7f.3577$iZ4.email@example.com...
>> >> My car's paintwork has been damaged by parking under a leaking air
>> >> conditioning duct. The car is now covered in a hardened chalky
>> >> coloured
>> >> martial , a bit like limestone.
>> >> It came off the windows OK using a stanley knife blade but I can't
>> >> shift
>> > it
>> >> off the paintwork. So far I've tried soap, petrol, white spirit, T
>> >> cut,
>> >> polish, vinegar and Cillit Bang.
>> >> Any other suggestions????
> I wonder if a clay bar would work?
What you need is a chelating agent that dissolves calcium salts. Have you
tried CLR or any of those other shower nozzle, electric kettle etc. cleaning
Another method might be to wet the area with bicarbonate of soda solution
(very mild alkali which turns the calcium to calcium carbonate), let that
dry then wash that of with acetic acid (vinegar, a very mild acid which
fizzes a bit as the acid dissolves the carbonate). It cleans oxide build up
off ceramic tiles and glass and it's not abrasive so it won't hurt