Zinc primer or epoxy primer

[luccass_j]

I'm doing the restoration on my W123 Mercedes. I started with sub frame that I removed and stripped it to bare metal. I was advised to coat it with POR 15 rust preventing paint. I preped the metal according to their instructions or so I think and the paint is peeling now. Fortunately I have done only rear axle carrier so it should be easy to redo. I'm not going to use POR 15 any more as I don't want to get myself in the same kind of situation.

So now I've got a couple of questions:

1. Can I use phosphoric acid to etch metal? And does anybody know any good brand?

2. Can I use Zinc Primer like Zinc 182 or should I use any other chassis primer e.g Eastwood Extreme Chassis Black Primer? And what is the difference?

Thank you in advance for all your help.

 

[ajlelectronics]

The POR-15 paint is something that I use a lot and have always found it excellent. However, it isn't really suitable for clean and bright metal, although keying it with Metal Ready can help. POR-15 excells where you have rusted metal. A few minutes with a wire brush and some pre-paint and you would have a job to damage the coating once cured. On smooth, bright metal, it will come off in sheets though.

 

[ajlelectronics]

METAL READY is Zinc Sulfate by the way.

 

[luccass_j]

Thank you for the reply Ajlectronics. The part only had a surface rust which I removed leaving me with shiny bare metal which is probably why the POR-15 is not taking.

 

[ajlelectronics]

Certainly will be! If the metal is that good, I use epoxy primer, then topcoat. I keep the expensive POR-15 for areas it is designed for... Chassis parts, rear axle and the like. Also bear in mind that it is UV sensitive, so any parts exposed to the sun need overcoating.

 

[luccass_j]

Do you use phosphoric acid to etch metal? or do you use epoxy primer on the metal?
That's one of the pictures I've taken. Now all the parts are apart.

 

[ajlelectronics]

Epoxy primer should take directly to that.

 

[steveo3002]

yeah go straight on that with epoxy , ive had issues with por15 too

 

[luccass_j]

Thanks it's the first time I'm doing this sort of restoration so once more thank you for all the help.

 

[richie00boy]

Definitely go with epoxy on that, don't use phosphoric as it could prevent full adhesion with some brands of epoxy. The epoxy should be topcoated as it will chalk with long UV exposure.

For info, Zinc182 is not really a zinc primer it just uses zinc phosphate to help adhere.

 

[luccass_j]

Thanks Richie00boy so I can go straight with epoxy I don't have to use Zinc 182 first?

 

[richie00boy]

That is correct, in fact putting another primer under the epoxy will make its performance worse. Epoxy is far better than zinc182 and any other single pack primer.

 

[luccass_j]

Thank you I will do it that way ill post some pictures

 

[Burdekin]

You can get zinc rich epoxy primers and obviously only worth doing if directly onto bare metal. But I've been told the zinc epoxies don't bond as well as epoxy mastic primers.

Interestingly a few years ago I did a little testing with POR and thought it was great but have just had to strip out a car that had damp carpet which I'd used POR15 and do some welding on. The POR came off quite easily in big strips even though prep was excellent so I now wouldn't use it at all anymore and the whole floor will be stripped again and painted with epoxy mastic.

 

[luccass_j]

Thanks again so what's the progress? I removed almost all the paint apart from the hard to get places like corners.

It looks nice and clean.

That's the hard to get places I'm talking about.

I should finish removing the last bits of paint this week and I still need to buy paint to put first to coats of epoxy. I also bought in line water separator that I didn't have the last time I was painting it with POR 15 I also want to buy another water filter to install it on my compressor.

Any suggestions or comments are welcome.

 

[richie00boy]

Epoxy needs constant temperature of more than 15 degrees Celsius to cure, for about 7 days. Just a thought at this time of year. I have used fan heaters and halogen floodlights before.

The cure will be speeded up if the object temperature is warmer, so if your object is say 30 degrees it will cure in about 3 days. It should detail the cure vs temperature the datasheet.

 

[andeep]

Make sure you abrade the surface to ensure you get no mechanical adhesion problems. Wire brushes tend to 'polish' the surface

 

[richie00boy]

That's good advice, it looks really shiny. I try to use polycarbide wheels as much as possible now. Leave a better key on the metal and although they can make flying debris it tends to be chunks rather than flying needles.

 

[luccass_j]

With 80-150 grid sand paper?

 

[andeep]

With 80-150 grid sand paper?

It should say on the primer tech sheet. For Lechler epoxy I have used 180-220.