Painting over steel that has been treated with phosphoric acid

[javelinadave]

The more I read on the subject the more confused I get. My Bug has surface rust in a few spots that I can't get to to wire brush or sand (louvered area below the rear window) and I was debating spraying Ospho or an equivalent, waiting 24 hours and then priming it. Anybody have any experience on the subject?

 

[Napalm00]

I did my radius arms using ospho/prep and etch.

• Stripped old paint
• Wire wheeled entire arm
• Wiped down with ospho and a China brush
• Rinsed with hose
• Dried in sun
• Self etching primer
• Rust-Oleum top coat

Lasted for years like this , super tough and zero rust.

 

[WreckITFrank]

Similar to above. Been doing this for a while and ironically quite a few places on my 91 Golf. I think as @Napalm00 said the key is to clean/wash the ospho followed by good etch. I'm into SEM, but I like paying way more for things because it makes me feel like it's better. I live 20 minute from Eastwood so have been through most of their stuff as well and have/had no issues.

 

[javelinadave]

Anybody ever not rinse off the Ospho and prime over it? That is my actual question. Half of what I read says yes and half says no.

 

[Napalm00]

I don't think it's possible. When I did above it created a thick translucent film on the part. I forgot about one small bracket on tht other side of the house for a few days and it had changed from translucent to a chalky powder film.

I'd assume the same would happen under the paint , making it flake off.

Edit: I forgot that I pulled the arms off to give to a buddy. Here they are 5 years later. Pre and post cleaning

 

[WreckITFrank]

i think you can spray and wipe off. maybe with some white vinegar solution or denatured alcohol.

 

[MountainD]

You have to remove it. I didn't on the bottom of one of my old door frames and the paint didn't adhere. I had just forgotten. The one I washed was fine. I am not sure about all brands--I just used the generic from home depot. I re-sanded, re-cleaned and repainted.

 

[BarryO]

Anybody ever not rinse off the Ospho and prime over it? That is my actual question. Half of what I read says yes and half says no.

Their website says to let it dry a minimum of 24 hours, brush off any powder that forms, wipe with mineral spirits, and paint. They should know.

Ospho

 

[hillstrubl]

Agree with above, I've had good luck with ospho (and naval jelly). They key is doing a few rounds to really make sure you get it in all the ridges, etc. I've used compressed air to dry, then rubbing alcohol or mineral spirits, Then paint.