What paint or primer to use under the undercoat?
 

I am finishing up the underside of the car with custom sheet metal work. The car was/is rust free and I want it to stay that way. I plan on reundercoating it at some point but for now I would like to paint the under side to keep it from rusting. However I can not decide on what type of paint or primer to use under the undercoat. Do I need a top coat under the undercoat or just a primer?

My thoughts are

A. Use a 2k Epoxy Primer / sealer.

B. Use a por15 top coat over metal ready.

C. other suggestions?

all you need to do is spray on one at most two coats of epoxy sealer then once dried spray the new chip guard over that.
no top coats are needed at any point for your under chassis rust and chip protection .

Just talking, 962. Not arguing in the least............

You can top coat without a downside to color match as original, right?

Single stage urethane with hardener seems a better product than BC/CC for this but again, just talking.

Bob, I did the full BC/CC under my yellow car.....while it worked and still looks nice after 20 years, it burned through a lot of product as the BC was quite thin in terms of coverage and the clear just made it look shiny near as I can tell.

When I do it again on my current car, I am just going to get a single stage colour match and paint the chipguard. Ought to cover better, use less product and will likely be more durable.

....but I am in no wise an expert...

Dennis

Cool beans.

If there is a problem with our thoughts, 962 would bring it up and best to listen.

Painting over is simply cosmetic.

Good luck. The schutz stuff is hard to screw up if you get the gun.

I was imprecise in my first answer, I actually applied the shutz over the epoxy primer I used and then I applied the base/clear coat.

Admittedly the layers were first a chromate (it was greenish) over the bare metal, then a good, heavy coat of epoxy primer, then schutz, then base coat, then clear.

Its been plenty durable but it did use a lot of the base coat as the schutz I used (dark grey Sikkens) showed easily through the almost transparent base coat.

Dennis

No you were not. I read it again. Also the title says under.

I was simply rambling about the top coat.

FWIW I do remember some kind of green Glasurit stuff I laid down on my panels that had bare metal on them. I don't even think you mixed a 2nd part with it. Bought it back when you could still get 21 Line Glasurit. Have never seen it again.