Many years ago a contractor got cement on a car I had. Cement (including dust) is a strong alkali which will damage the paint as much as an acid would. I would speak to the contractor (he has insurance) and this should be taken care of by a GOOD body shop. Even once I had had the cement removed, it had damaged the paint (didn't really show up for a year or so...) Basically the car was ruined. I sure wouldn't wait for 'time' to remove it, it is something that needs to be taken care of asap...and by a professional. It will be expensive too.

John N