Question on Phosphoric acid rust converters

[nfernandez]

I just bought a used 60" snowblower attachment that was kept outside by the previous owner. There is a fair amount of rust on it, but also some dull old paint. For those that have used phosphoric acid, do you just apply it to the entire surface to make sure you get all the rust spots? Then paint a primer over that? I'm not sure if you put phosphoric acid over old paint if that would cause any issues, but I don't want to miss any small rust spots. Thoughts?

 

[flusher]

I use Gempler's stuff. Just paint it on the entire surface, clean it off with a rag or paper towel after the recommended time, primer then top coat. Seems to work OK for me.

 

[rswyan]

I'd avoid getting it on good paint (paint that is well adhered ...)

On the rusted areas, remove any (heavier) rust (wire wheel, flap disc, etc.) as much as possible and then spot treat the specific areas.

 

[C4Ranch]

I just bought a used 60" snowblower attachment that was kept outside by the previous owner. There is a fair amount of rust on it, but also some dull old paint. For those that have used phosphoric acid, do you just apply it to the entire surface to make sure you get all the rust spots? Then paint a primer over that? I'm not sure if you put phosphoric acid over old paint if that would cause any issues, but I don't want to miss any small rust spots. Thoughts?

Yes. I've got it on paint and no ill effects. It seems to soften it but then I paint right over it.. Fine for my trailer/implements. It's not a show car.

 

[Gary Fowler]

You should sand the old paint and feather the edges prior to putting on new paint so I would sand first then acid treat. The acid I have used before (WEDAC) does nothing to the paint, just bare metal ( rust ) is affected.