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Old 10-25-2008, 08:10 PM
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Can primer be left without a topcoat?

I started spraying Dupont DTM 25xx epoxy primer the other day and realize this project is going to take a lot longer than I anticipated. So, I'm wondering if it is okay for this primer to be uncoated for long periods of time? I'll be doing sections at a time so there will be areas with "old" well-cured primer and other areas with fresher primer. I have a lot of bodywork to do and still need to drive it around every once in a while also, so it will see some sun/weather.

Oh, have another question...when primering in sections, what's the best way to do this? I guess what I'm asking is if you have to do half a panel at a time, how do you deal with the overlapping areas? Hope that makes sense?

Thanks, Scot

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Old 10-26-2008, 05:05 AM
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Epoxyprimer can be left without a topcoat period, Most of the flat black rat rods are just ppg dp 90,
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Old 10-26-2008, 12:47 PM
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Thanks, it's a relief to hear that! Will it turn chalky and/or have adhesion problems with 2k primer later? Is Dupont epoxy comparable to the PPG stuff you mentioned?
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Old 10-26-2008, 01:07 PM
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Quote:
Originally Posted by ScotY
Thanks, it's a relief to hear that! Will it turn chalky and/or have adhesion problems with 2k primer later? Is Dupont epoxy comparable to the PPG stuff you mentioned?
------------------------------------------------------------------------

Not inside it won't chalk but even if it did the nice thing about epoxy is it breaks down from the outside-in so all you do is scuff with 180 to get rid of the dead epoxy and re-epoxy.
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Old 10-26-2008, 02:00 PM
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Your in the same spot I'm in, I just completed all the body work on my '33 Ford and will let it sit till next spring/summer before we complete the painting portion of the job. Primer is not a top coat as you know and is very porous, which will allow moisture to work it's way down and under the primer and rust the metal below. As long as you keep the car in a dry and preferably low moisture area, it should be OK till you apply the paint. Just remember that when the time does come to paint the car, you will have to re-sand the body and re-apply a fresh final coat of primer, followed by yet another round of sanding and it all goes well, a coat of sealer then base coat. Good Luck.
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Old 10-26-2008, 06:59 PM
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Thanks for the info, Barry! Good to hear that! You REALLY need to get a distributor for your products here.

yknot,

That is a good point and I should have included that in my original question. I've always been told that primer is not waterproof, not designed to be left uncoated, will absorb water, etc. Is epoxy going to be different? I live in a very humid climate and we're coming up on the rainy season. The carport doesn't keep all the water out and I need to move the vehicle out fairly often.

I'm kind of thinking, from all the things that I've read here, the easier to sand something is, the more prone it is to absorb water. I haven't sanded the epoxy primer yet (Dupont) but everyone says it's tough to sand. If my assumptions are correct, that's a good thing for my situation.
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Old 10-27-2008, 04:31 AM
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When you sand get some 220 wet snding paper and wet sand it, it may go a little easier.
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Old 10-27-2008, 08:49 PM
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Quote:
Originally Posted by yknot
.....Primer is not a top coat as you know and is very porous, which will allow moisture to work it's way down and under the primer and rust the metal below. .......
Really?? I always thought epoxy primer had good water resistance.
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Old 10-28-2008, 12:25 AM
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Epoxy primer is the only primer that is waterproof. I had sections of my Mercedes in epoxy primer for over five years with no problem. This is in Portland Oregon where the winters are very damp. I used both PPG and SPI epoxy and when it finally came time to paint all I had to do was scuff the epoxy, like Barry said, and lay down a fresh coat.
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Old 10-28-2008, 07:53 AM
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My DP90 is getting killed by the sun, after six months it looks pretty bad. A little color sanding makes it look ok again but I plan on putting a topcoat on it......it's tough stuff but not much (if any) UV protection.
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