Unlike POR-15, POR-20 is actually not meant to be painted over rust,
much to my disappointment. Called the company to double-check, after all
doesn't "POR" *stand* for "Paint Over Rust"? The sales lady wasn't so sure
anymore and guessed that "maybe a little bit of rust" would be OK. Ha!

Being tired, I took the chance and painted the aluminum colored paint on
both new and superficially rusted parts. So far, the bus wasn't driven
much, perhaps 40 miles, the longest trip being just about 20 miles. 

1) The paint flaked off at just one matchbook sized spot: I suspect that
the area wasn't perfectly clean before it got painted, perhaps smudged by
a greasy thumb. 

2) Parts that were shiny and perfectly clean before being painted still
look great. 

3) The paint layer on parts that were not completely rust free now has
tiny goose bumps, as if there were lots of tiny air pockets between the
paint and the metal.

Preliminary conclusion: this stuff is better than the usual BBQ paint,
which has never worked for me. However, you really gotta follow the
instructions. It's also expensive: $24 for a pint, but goes a long way.
Used only half the can to paint the entire exhaust system from headers to
tailpipe (except the heat exchangers, which were painted with the original
POR-15). 

-- 
Sami ('75 Westf.)
dakhlia@wuecona.wustl.edu
http://wuecon.wustl.edu/~samid/