Surfacer then epoxy prime? Or vice versa?

[enkeivette]

I've been told to shoot the epoxy primer, then a surfacer like slick sand, then block it, then respray more surfacer, then paint. But why not spray surfacer, block sand, then spray epoxy primer, then paint. This way you would save youself a step. But I honestly don't know, I'm looking for advice.

As for the color, here is the closest I could get to a graphite stripe. I misted the carcoal over silver and somewhat over the black to give it a metallic look. As for the actual color, I'll probably use PPG dark slate grey for the stripe, (the Viper color) and maybe the Porsche metallic black for the rest of the car.

Here's the graphite with metallic black:



Here's the original concept with the charcoal:

 

[MYBAD79]

The primer/surfacer is hygroscopic, means when you wetsand the moisture will soak down to the fiberglass or sheetmetal or filler/Bondo whatever is under the primer.

I would seal the bare material (metal or fiberglass or SMC) with Epoxy, for example black or red... then shoot a few coats of primer. Then when you sand you know when to stop when you see the different color epoxy coming thru.

Once the sanding is all done you can shoot another coat of epoxy sealer to seal the primer - the base coat and the reducer are then not penetrating into the primer.

I'm sure SMYDA can go into more detail, he's way more experienced than I am :thumbs:

 

[Belgian1979vette]

I think smyda is on holliday, but your explanation seems correct to me.

 

[enkeivette]

So there's a third type of primer? Epoxy sealer? :huh:

So it's:
1)Epoxy prime then,
2)Primer surfacer (urethane?) then block sand. Then,
3)Epoxy sealer?

How much of this stuff do you need? About a gallon of each?

 

[MYBAD79]

Most epoxy primers are sealers. They say to add 1 part urethane reducer (if it's a 2:1 ratio epoxy and hardener, many times they say to add 1/2 part if it's 4: ratio)... read the tech sheet that came with the primer.

The way I understand this whole sealer thing: If you do NOT use a sealer you will have many coats of urethane primer and potentially the fiberglass soaking wet. It will take forever to dry the car before you can apply paint. For example if you did not use epoxy first and you wetsanded the car and then don't wait until it's dry, the next coat will lift as soon as the moisture in the previous coat is evaporating...

I bought 1 gal epoxy primer and 1 gal urethane primer for the Karmann Ghia that I am working on - a gallon is a lot cheaper than buying f.e 3 qts.... that Kustom Shop epoxy from TCPglobal is a pretty good value for the money. PPG DP epoxy is better bu 4X the price. I like PPG shopline urethane primer but it's also more expensive than Kustom Shop. The shopline seems to build higher/thicker.

 

[big_G]

FWIW, here is how we do it at my shop:

Bare fiberglass > epoxy primer (optional) > urethane primer/surfacer, wet sand
or
Bare fiberglass > Evercoat Slick-sand (or similar high build primer/surfacer). Only needed if the substrate is very wavy requiring block sanding or glass strands close to the surface. Dry block sand only > primer/surfacer, wet sand
or
Bare fiberglass > primer/surfacer, wet sand

Epoxy primers (over fiberglass) and urethane sealers (prior to top-coats) can be used if desired, not usually necessary.