Epoxy Primer Issue

Duane WI

Member
I made a new box for my 52 Chevy pickup 3 years ago. It was made with new 16 gauge cold rolled steel. I used Omni epoxy primer to seal it up. The metal was clean and degreased before priming. I put the box in the corner of my shop for storage as I worked on the rest of the truck. Yesterday I looked more closely at the box and noticed little rust spots. There are about 20 small rust spots in random areas. There is one cluster of about 20 more rust spots. The cluster is about 5 inches in diameter. Each rust spot has a small area about 1/16 to 1/8 inch in diameter that the primer has lifted. The paint around the rust spot is stained with rust. The rust stain can be wiped off leaving the small spot of rusted metal. Here are some pictures. The one picture is the box right after it was primed. Any ideas what happened? I am thinking I must have had moisture in the compressed air. Do I strip it all off or just spot sand and re-prime. I am thinking that 3 years is enough time for issues to show up and I can just spot sand the troubled spots.
mvphoto39044.jpg


mvphoto39045.jpg


mvphoto39046.jpg


mvphoto39047.jpg
 
That definitely shouldn't have happened. The only reason I can think of is the product was defective. The metal maybe should have been roughened slightly but that at most would have caused adhesion issues. The primer has failed. It should have sealed out the moisture.
 
I did hand sand the surface with 150 grit sandpaper before I wiped it clean with wax and grease remover. I can't figure this out. No sign of any issues after I painted it or even a few months after when I put it in the corner for storage. I put boxes full of truck parts in it and noticed the rust spots yesterday when I started looking for something in one of the boxes of parts.
 
The cardboard boxes can absorb moisture from the air and become damp but the epoxy primer should have blocked the moisture from getting to the metal. The only time you should get rust on metal primed with epoxy is when the primer is damaged down to the metal and then the rust should be isolated to just the damaged spot. Most other primers are porous where water can penetrate right through if kept wet long enough and rust under the paint. Completely sealing the metal is what sets epoxy apart from other primers. I think the product you used must have been defective.
 
At this point I think I am going to sand all of the spots to bare metal and treat them with phosphoric acid. Then give the rest of the box an aggressive scuff sanding with 180 or 220 grit and spray two more coats of epoxy. Any suspicious spots I find I will sand to bare metal. I think the half gallon of epoxy I have in my basement is going to get thrown out.
 
It's obvious by the "pattern" that it was from contamination. It's NOT random like faulty primer would be. I will agree with the poster below that says "Omni" is junk..BUT only the paint/top coat. Their epoxy is exactly the same as PPG top line "DP" primer. Only difference is the induction time (Wait after mixing) is a little longer for Omni. I've used PPG and the Omni epoxy since the mid '80,s in auto body/restorations and there's nothing better. Just sand off where the pattern is and re-prime those areas when you are ready to paint.
 
Seeing that you are going to the trouble of sanding down and treating the contaminated or the rusting areas where moisture and rust is bleeding through, it may not hurt to do the same in a couple unaffected but hidden areas to see if rust or lifting is just starting to occur. A couple exploratory areas may show further issues or not and help you decide if those bad areas were just problematic and localized.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top