[Shop-talk] Chemical rust remover?

[Karl Vacek]

> *I bought at our local Home Depot:*
> *a Klean Strip product:*
> *"Phosphoric Prep & Etch" which is sold for rust removal and concrete
> etching.  $13.00 a gallon.*
> *If I remove the surface rust mechanically, it has been a permanent rust
> stabilizing prep before priming and painting.  That is including pits and
> small craters.  Someone clever explained that the acid converts oxides to
> phosphates which are stable and over the years, it's worked well for me.*


Absolutely.  Phosphoric acid is the active ingredient in most "metal prep" 
priducts, and it works on aluminum too.  For a final treatment, you might 
want / need to use a conversion coating product, typically available at 
automotive or industrial paint jobbers.  You'll know if you need it, ,if 
flash rusting occurs after you wash off the phosphoric acid.

Given that you're working on a wood stove, I'm not sure that you would have 
good luck with Locktite "Rust Reformer" or the latex-based products, due to 
the heat, but for other things those products are a nice shortcut, leaving a 
durable and paintable black finish where the rust once was.

I've recently discovered another power of phosphoric acid.  You know how 
it's virtually impossible to thoroughly clean brake calipers, wheel 
cylinders, etc. without blasting them ?  I still haven't built or bought a 
blast cabinet, and I hate to pay for that work, particularly on stuff that 
could be ruined by a careless workman.

After trying every other cleaning method I had available and still having 
some brake dust and rust embedded, I soaked some cast iron caliper halves 
and wheel cylinders in diluted phosphoric acid solution.  Like magic !  It 
removed all the residue, rust, even paint in the corners I couldn't easily 
reach.  It does stink though - gotta do it outside or in a detached garage.

One caution -- don't leave stuff, particularly steel, soaking for more than 
a couple of hours.  Cast iron is pretty impervious and I've left it in for 
days, but I ruined some steel brake bleeders by soaking them too long.  The 
acid ate the sharp parts of the threads off, and they easily stripped.  The 
threads in the iron were perfect - I just had to replace the bleeders.

Karl