Reworking an old steel barge

Rusting etches the surface sure . But Standards require a specific surface roughness from sand blasting so there's not much gain there. And light rust is fine.

 

I am *NOT* recommending this, but I've rolled out excess Jotun 605 primer onto my steel gantry which had fairly heavy rust on it. The paint has bonded well with the rust & underlying steel - you can abrade it off but it doesn't chip or flake off. Apparently (according to the supplier) this paint is also somewhat tolerant to moisture during application.

For myself, I'm overcoating clean primed plate or plate wiped down with methylated spirits. For some reason I don't understand, bare steel doesn't seem to rust in my shed.

PDW

 

Peter
If you look at the powder rust that blooms on a fresh steel surface it's very poorly adhered globular specks which does absolutely nothing to promote paint adhesion and can be wiped off with a cloth.

I have seen steel weathered to remove millscale then wire brushed and painted with epoxy and it worked very well but that's new steel.
But if you sand blast as asked about above then you have your ideal key and the paint manufacturers will stand behind you. Maybe

 

Yeah, maybe. I did get told that, if I didn't blast or otherwise remove the mill scale, they didn't even want to sell me the paint let alone stand behind it. So I did.

I find that blasting puts a much better 'tooth' on the steel than grinding does whether using a flap wheel or hard grinding wheel. However it's a terrible job. I used to think I hated angle grinders before I discovered sand blasters. When one compares the 2, I find that I merely dislike angle grinders. The bright side is, I've almost finished.

Anyway, my observation is that the Jotun 605 epoxy paint is tough as hell and binds rust so works well on imperfectly cleaned surfaces. It is obviously going to work better on a properly prepared surface.

PDW