I steam cleaned my car after it was stripped of parts and on a rotissiere. It was bare metal with no undercoating at all when I got done steam cleaning it and it only took 3.5 hours to strip it of all undercoating. Perfecty clean ready for sheet metal replacement.

Now I'm ready for sheet metal replacement on jack stands in garage to insure nothing moves.
Then after all the sheet metal replacement I will lighty media blast the whole thing before paint.

Lucky I can do it all in my backyard and the car never leaves my place.

If you have time checkout my thread about my most recent car, I have done 2 cars like this so far. web page