How thorough should I sandblast old rust/paint before applying POR15/primer?

[SpringHollow]

Just a note of caution. I recently redid my tractor rims, sand blasting to bare metal, phosphate washing, etc. I primed with an expensive epoxy primer and then used an expensive top coat with hardener. When i was done, I let the last coat dry for a week. I was extremely disappointed in the results. Where things banged against them, it chipped to bare metal. If i jad used cheap TSC paint, it would only show at the point of contact whereas with the epoxy stuff, it chipped out a larger area.

Ken

 

[strum456]

Just a note of caution. I recently redid my tractor rims, sand blasting to bare metal, phosphate washing, etc. I primed with an expensive epoxy primer and then used an expensive top coat with hardener. When i was done, I let the last coat dry for a week. I was extremely disappointed in the results. Where things banged against them, it chipped to bare metal. If i jad used cheap TSC paint, it would only show at the point of contact whereas with the epoxy stuff, it chipped out a larger area.

Ken

Your problem is most likley the phosphate wash. If it is not neuturalized properly, it will leave an acid film that will keep primer or paint from sticking. The best way to neuturalize any of those rust treatments is to NOT USE THEM!

Blast your steel the best you can. Blow off the blast media with compressed air. Use a spray bottle to spray on waterborne wax and grease remover and wipe it off with a rag as you go. Use a scotchbrite pad to clean off the fuzzies from your rag. Blow off the scotchbrite dust. Drag it with a blue (automotive) tack rag. Spray epoxy. I have not seen anything that holds up like Southern Polyurethanes Epoxy Primer. You can beat southern polyurethanes epoxy with a hammer and it wont fail until the steel yields. I cant say the same thing about POR 15. Not to mention, POR 15 is very tempramental in a number of different ways.

 

[SpringHollow]

Thanks, Strum. I have 4 more to do this Spring so I will try what you say and compare. Some places say not to neutralize your phosphoric acid. I tried it both ways.

Ken

 

[Luremaker]

..... I have not seen anything that holds up like Southern Polyurethanes Epoxy Primer. You can beat southern polyurethanes epoxy with a hammer and it wont fail until the steel yields.....

I do not want to hijack this thread but do you know if Southern Polyurethanes Epoxy Primer will stick to chrome/nickel plated metals?

 

[strum456]

I belive it will. Any steel to be painted should have a blast profile or 80 grit da scratches. As long as your surface has been abraded by one of these two methods, I think it would work. However, when in doubt, just call Southern Polyurethanes. Their customer service is second to none.

My opinion on rust convertors such as phosphate and rust encapsulators such as por15, is that they are just a gimick. I dont know of any reputable restorers that recommend these products, but I know quite a few that gasp at the first mention of the stuff.

 

[SPIKER]

My opinion on rust convertors such as phosphate and rust encapsulators such as por15, is that they are just a gimick. I dont know of any reputable restorers that recommend these products, but I know quite a few that gasp at the first mention of the stuff.

the sandblasting is very good but it leaves dusts & silica's on the surface which causes the paint/primer to gap over them (paint/primer floats over it on a layer of silica dust/material very similar to oil on the surface.) on a molecular level the best surface to paint on is a heavy phosphate treated sandblasted surface. The phosphate treatment material cleans and etches the rough surface is helps paint stick & removed the left over sandblast issues. Though too rough and the paint will look bad without sanding and applying further coats to smooth out the paint finish.

Mark

 

[strum456]

The metal prep method I previously outlined has been consistently sucessful for me. It is also the exact same method used by some very talented automotive restorers that I frequently share ideas with. If it works on the cars at Pebble Beach, Barret Jackson etc., it should be okay for your box scraper.

Stay away from all metal treatments.