I have a rust issue to deal with, and just wondering about phosphoric
acid vs POR 15.

 From Wikipedia ( and my college chemistry so long ago)

Phosphoric acid (From Wikipedia and my college chemistry so long ago):
Phosphoric acid may be used as a "rust converter", by direct application
to rusted iron, steel tools, or surfaces. The phosphoric acid converts
reddish-brown iron(III) oxide, Fe2O3 (rust) to black ferric phosphate,
FePO4.

"Rust converter" is sometimes a greenish liquid suitable for dipping (in
the same sort of acid bath as is used for pickling metal), but it is
more often formulated as a gel, commonly called naval jelly. It is
sometimes sold under other names, such as "rust remover" or "rust
killer". As a thick gel, it may be applied to sloping, vertical, or even
overhead surfaces.

After treatment, the black ferric-phosphate coating can be scrubbed off,
leaving a fresh metal surface. Multiple applications of phosphoric acid
may be required to remove all rust. The black phosphate coating can also
be left in place, where it will provide moderate further corrosion
resistance (such protection is also provided by the superficially
similar Parkerizing and blued electrochemical conversion coating
processes). 8 oz bottle cost's $8 bucks. Covers 20 sq. ft.

POR-15: converts rust, turning black in the process. Doesn't sound much
different than the Phosphoric acid - but at twice the cost. Don't know
much more, but that it's popular.

Anyone know more about the differences?

John

--
John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com