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unstable 07-20-2003 06:34 PM

Phosphoric Acid + Prevention of flash/surface rust
I just wanted to let everyone know about my experience in using phosphoric acid (metal etch/floor etch/metal conditioner).

A gentleman on the Hobart Welder forum recommended using it to neutralize rust.

I've got most of my sheetmetal in my basement (being that I do not have a garage). It takes time to manually strip through all of the years of paint, primer and filler. In the meantime, surface rust has appeared on many of my panels. It really doesn't take long for it to rear its' ugly head, 3 days at the most around here.

So I picked up some stuff called "Floor Etch" which is just phosphoric acid, and I've layered it on the bare metal...and I just have to say, the stuff is phenomenol.

Wearing rubber gloves and protective eyeware, soak a rag in the acid. On light rust, it will actually wipe it away in a few least it appears to.

On non-rusted bare metal, it puts a sort of grey-frosting on it. TO my understanding, you should actually hit bare metal with this stuff, it helps the primer adhere.

On somewhat thicker rust, I just pour the acid right onto the metal. If the panel doesn't have any holes in it, you can tilt it around and get full coverage. It will turn the rust into a hard black substance...not sure what it's called chemically.

Another good method is soaking a rag, smearing the stuff around, and leaving the drenched rag on the metal. The rusty areas will turn black.

I've also used a wire brush when I'm applying the acid. Kind of brush the acid around with the brush and at the same time you're brushing away little chunks of cancer.

At the end of the day, it APPEARS that this stuff at least SLOWS the rusting process substantially. I cannot say whether it completely stops the rust...I'll let you know in a few years.

I recommend at least trying this stuff where you would not use por-15. It's cheap..and I just wish I would have known about it sooner.

Hope this helps someone out.

crazy larry 07-20-2003 07:25 PM

por15's METAL READY is a zinc-phosphate etcher, and i've left parts unattended for weeks without ANY rust appearing.......

unstable 07-21-2003 06:12 AM

metal ready is a tad more expensive. Price difference is neglible. I'm just putting the information out there for whoever is interested.

asennad 07-21-2003 07:36 PM

The problem with PA is that it only gets the surface rust. If the rust has any thickness at all it will only change the top layer of rust and leave the sub-surface untouched. I would hit any rust with a 60 grit sanding pad to ensure that there is no rust left to rear it's ugly head down the road.

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