The Stovebolt Site Forums The Shop Area Paint and Body Shop Muriatic Acid

I got 0 results back when i searched muriatic or hydrochloric acid.



I used to clean pools and can tell you there were some awfully clean bare metal spots in the bed of my truck from the muriatic acid drips. The price difference makes this acid tempting compared to phosphoric. Body shops seem to use only phosphoric. Anybody know why? Are there any problems in using this to etch and/or clean metal before painting?

Phosphoric acid is much safer to work with. I use muriatic acid to clean/etch old gas tanks. I wouldn't use it to prep metal for body work or paint. It's far too reactive to be safe.

Muriatic acid is reported to cause hydrogen embrittlement in steel.

Phosphoric acid converts the iron oxide (rust)to iron phosphate. The iron phosphate inhibits the formation of new rust.

neilroy nailed it.

As stated in The Standerd Guide to Automotive Restoration by Matt Joseph an old but very helpfull book, the use of muriatic acid has "slipped into disuse and properly so. This is a lost art and should remain so." I use phos only when I must and try not to.

Thanks for the input, men. After further reading, online, HCL does well to remove the rust but can also be harsh on iron itself (and removing iron from the steal alloy would definitely cause embrittlement). The reaction produces a liquid solution (no protective layer as with iron phosphate). And it is dangerous to use (but what isn't...). So it looks like everyone is right on this one.

I'll probably still try it, though

Thanks, again.

I purchase Phosphoric acid at Home Depot. It is in the paint section as a metal prep. Lowes does not carry the same product in my area. It is 13 or 14 dollars a gallon.

Thanks, Lonnie. I bought some and I'll try it too. It looks like it's only 50% acid. Will paint/body shops have 100%?