On Sun, 28 Jun 2009 01:50:03 -0400, wrote:

If you don't mind working with pool acid it will do the trick. I have
taken shower doors from one of my rentals outside and laid them on the
grass and poured pool acid on them and scrubbed with a long handle
hard bristle broom like you'd use around the house to sweep stuff into
a dust pan. You want to be careful not to get acid on yourself, wear
eye protection, etc. But it will work and fairly quickly. It didn't
even seem to hurt the grass. Hose the area down well when done.

The problem with that is hydrochloric acid eats the aluminum frame of
the door.

Agree with you about hydrochloric acid. A milder acid is Sulfamic
Acid (by TILELab), made for tile, grout and concrete. Mix it weak and
I'm guessing no harm to metal frames. Of course rinse frequently.