Your thoughts on phosphoric acid dilution as a metal prep cleaner and tooth structure builder

[Moparfiend]

I know the vapors are not good and to use great care and proper PPE what are your thoughts? I have used it after hydroblasting sheet metal and darn if it doesn’t prevent flash rust. Works really well for me. But I don’t know anyone else who uses it. Would be very interested in anyone who would like to comment……

 

[Grabbergreendream]

I use it. It works great for me on clean blasted steel if they have to sit forany length of time before priming to prevent flash rusting. I always scuff everything before wiping it all down with lacquer thinner before priming. Works for me.

 

[Moparfiend]

I use it. It works great for me on clean blasted steel if they have to sit forany length of time before priming to prevent flash rusting. I always scuff everything before wiping it all down with lacquer thinner before priming. Works for me.

What dilution do you use?

 

[zyzzyx]

I use it on all bare metal to "phosphorize" the surface so I will get good adhesion of the epoxy primers.
I use it 50/50 and the brand is Kleen Strip I believe. Home Depot paint Dept. It gives the surface a slight
rainbow effect.

 

[Grabbergreendream]

I use it 50/50. I brush it on & will leave it for a few days to "etch" into the metal. I use the same Kleen Strip prep & etch from HD that zyzzyx uses. Its got a greenish tint. Sometimes it'll push up some white powder residue that dries & sticks to the surface. It comes right off with scotch-brite red pads, or you can re-apply some more on a rag & wipe it off, but then I have let it dry. Phosphorus acid is nowhere near as dangerous as muriatic acid. I had a buddy invite me over for some beers years ago. When I got there he was flushing a radiator in his garage with muriatic acid. He spilled a bunch draining it & trying to rinse out the radiator. Fumes were pretty bad & he decided to leave things & come back the next day to let the garage air out. I stopped by later that week & he showed me all kinds of bare metal in his garage that had rusted just from the vapors in the air. Things like the chain on his door opener, blades on his table saw. Other bare steel tools, the man door hinges. I'll never EVER use muriatic indoors after what I saw...I dont even store the bottle in my garage, its inside a 5-gal pail with a lid behind my garage. Phosphoric is a much better alternative, but both have its place...

 

[SlinktRR]

Why they don't call muriatic what it really is, hydrochloric acid, I will never know. Phosphoric is a weak acid, key ingredient in cola when diluted. When concentrated it will irritate but it won't be as dangerous as sulfuric muriatic or hydrofluoric. Sounds like a good way to treat bare metal.

 

[zyzzyx]

The Phosphoric acid actually leaves a coating on the metal substrate. Hydrochloric does not!
It must be rinsed with water and dried immediately.

 

[hunt2elk]

I like using phosphoric acid as well, but isn't it very important to wash it off thourorly with water before priming to neutralize?

 

[451Mopar]

The roof of the '69 Coronet 500 had some surface rust. Stripped the roof to bare metal, treated with the acid, went back over it with scotch-brite pad to remove the white powder residue like GrabberGreenDream posted. I even hit it with a coat of etching primer before coating with DP-40 2K Epoxy primer/surfacer. That was about 20 years ago, and no sign of rust. Someday I hope to put some paint on it (maybe this summer?)