[TheForge] Phosphoric Acid

[paul]

Cindy and James wrote:
> 
> All this about phosphoric acid, I have a question.
> 
> Have any of you used it and then painted over it?  Exactly what was the 
> procedure and what was the long term result?
> snip<
> 
> 
> James Allcorn
> Bois D'Arc Forge Blacksmith Shop
> Paris, TX
> _______________________________________________

I have used a PPG product , Metal prep, under paint. It was used on 
sheet metal that had the primer removed and exposed bare steel. The 
surface develops a oxide layer very quickly and the metal prep was used 
to clean off the iron oxide and micro etch the surface to receive 
primer. The metal prep was always followed by a water wash and a solvent 
wipe and then painted, hours to minutes, not days between actions. They 
also list some conversion products on the following web site.
see:

http://www.tcpglobal.com/autobodydepot/rustremove.aspx

If you look at this:

http://en.wikipedia.org/wiki/Phosphoric_acid

you might see where the white powdery substance might have come from... 
the passage from the wiki
"Orthophosphoric acid is a very polar molecule; therefore it is highly 
soluble in water" would seem to indicate that given the slightest 
opportunity the residual crystals of Orthophosphoric acid would absorb 
moisture from the atmosphere and wreak havoc from there.
Did you follow the application with a water rinse? The only place I have 
used the phosphoric acid solution has been on sheet metal... no 
crevasses to remove the residue from.

-- 
Paul Sperbeck
WB9HCO
jadap

  "The difference between genius and stupidity is that
genius has its limits." -Albert Einstein
"Life is hard...it's harder if you're stupid" John Wayne - Sands of Iwo Jima