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Old 10-06-2011, 01:34 PM
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Get Ready to Topcoat or Seal first

I have already epoxied the body and applied a high build urethane primer. The primer has been sanded in most places with 220 grit paper, dry. The high build left a lot of orange peel and required some pretty extensive sanding. As a result I have sanded a lot of the high build off and have reached my epoxy in some places.

My question is: should I apply another coat of the urethane primer 1) as a sealer, 2) as a medium build, or 3)finish sanding with 400, then 600, and topcoat?

See pictures for reference...

Also, top coat is a single stage urethane (Gloss Black Delfleet essential, specifically)
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Old 10-06-2011, 09:55 PM
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That's a lot of sand-thru; how does it feel when you run
a hand across it?

If it is smooth and feels good, I'd spray a sealer coat
and then topcoat it.
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Old 10-07-2011, 10:18 AM
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The spots that I've sanded are really smooth, they only have scratches from the 220 I've been using. The spots I haven't touch yet are rough.

Rather than continuing with the sanding last night, I decided to remove my sunroof panel and finally managed to remove the side view mirror that had been stuck from the cars last paint job (I;'m assuming they painted the car with the mirror on).

I picked up some reducer this morning and plan on doing what you've recommended: finish sanding, seal and top coat. If I had more room, I would remove the hatch as the spoiler (which can't be removed) hangs over the side of the rear quarters. The solution is to keep the hatch open while painting, but it creates a sharp angle where the hatch matches up with the roof line. Consequently, I may end up painting the hatch separately--we'll see.
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Old 10-07-2011, 03:47 PM
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Guaranteed, you will get halos around each sand-thru after spaying sealer.

Which leaves you with a couple of options, sand the sealer (if it's one that CAN be sanded) or, spray your base on top, sand that and then spray a final coat of base.

Some sealers (and some epoxies) are not sandable. I use a reduced epoxy (that is sandable) for a sealer.

Addition:
I just thought of the possibility you are using ss (that you don't intend to color sand) and not bc/cc.
If that's the case, I would shoot a coat of sandable epoxy, block it with 400, then shoot another coat of reduced epoxy as a sealer before your topcoat.

I'm not saying that's the only way to do it. But, it's what I would do.

Last edited by roger1; 10-07-2011 at 04:04 PM.
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Old 10-11-2011, 11:26 AM
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Yesterday was a bad day. I finally finished sanding the car, bumpers, trim pieces, etc,. and decided to spray the second half of the urethane as a sealer (reduced) thinking that it would be much smoother...

While it sprayed much faster this time, it went on too wet (my fault for not setting up the gun properly I'm sure) and it is almost as rough as the first time and has lots of runs. It wouldn't be so bad if it only required a little sanding, but I always have to go really deep as I get little pin holes. What is causing this?

If I have to sand this all the way down again: 1) I'm going to have a nervous breakdown; 2) I'm not going to use this primer ever again; 3) I'm going to pick up more of the epoxy primer and spray a couple more coats of that instead. The epoxy sands WAY easier than the high build and it goes on way smoother to begin with.

It takes me almost as long to clean out the garage after sanding, in preparation for paint; as it takes me to sand the damn thing. I also forgot to spray a couple of pieces yesterday, which just added to the frustration. But, in retrospect, I'm glad I hadn't, because I would have had to sand it all over again anyway.

I'll post some pics later, but basically they will look like the previous ones with way more runs. FWIW, I'm using a 1.7mm tip. Should I have used a 1.4, as the primer was mixed as a sealer?
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Old 10-11-2011, 12:13 PM
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Little pin holes that develop after a few minutes up to around 30 minutes after are called solvent pop.

It's caused mostly by spraying to thick of coat or while doing multiple coats without the proper flash time in between. Improper reducer temperature can play a part too.

Solvent pop is a nightmare. Not as much so with primer but with the topcoat is sure is. Nothing worse than having to sand off all your $300 per gallon paint. At least your primer was cheaper.

Yes, you are better off taking off at least down to where the pinholes are gone. Since you have solvent pop, you probably also have trapped solvents. And that's a really bad thing.
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Old 10-11-2011, 02:12 PM
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Thanks for the insight. Last time I sanded, I just used 220 right off the bat. What is the coarsest grit I can start with that will allow me to get through this process a little quicker?
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Old 10-11-2011, 02:16 PM
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Are you going back down to metal?

Then I'd say 80.

If you're going to try to not disturb your epoxy, you'd have to be pretty careful with that. So, maybe 120. Hard to say, I don't know how you are sanding and how careful you are.
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Old 10-14-2011, 01:30 PM
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Paint.

Hi.
Just thought I would throw in my thoughts. Forgive me if this is redundant to you.

The reason you are sanding through in some spots is because those are the high spots. The low spots are rough because they don't get sanded. of course I'm assuming you are using a sanding block and not just your hand, which will cause even more trouble...
You need to apply more high build primer and sand it flat with a block using 220/320 grit paper. You will need to apply more primer in a different color, or a light coat of a contrasting color until you knock down the high spots and fill the low spots. (called a guide coat)
I have found that if you tint the last coat of primer you can get an idea of how flat and smooth the body is since the tinted primer has a bit of a sheen to it. If it looks good then your final sanding must be with 600 paper wet before applying the top coat. (tinting with your top coat color will also help your top coat to cover quicker as well)
Sealer is not generally needed at this point, just clean with wax and grease remover, tack and spray.

Good luck.
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Old 10-16-2011, 10:45 AM
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I would have to agree with Hemi...............seems like you may have some issues with the body yet .......if you are going to reprime which sounds like a good idea take your time between coats......let it flash..........assuming your using a urethane 4 to 1 type prmer try mixing it 4 parts primer 1 part hardener/activator 1 part urethane grade reducer.....will help it flow out a little and not leave quite as rough.Let it flash off 15/20 minutes between coats....Use a guide coat as Hemi suggested__darker or lighter coat for contrast to your primer.............and start blocking with 120 on a longboard or a paint stick......use the 120 grit just long enough to break through the guide coat with no spots leftif you go through the guide coat and the primer you have some high/low spot issues which you may have to fix. If no issues after blocking with 120 spray a light coat of black for a guide coat again and proceed with 220 /320 or whatever you are going to finish sand with...as fr the second guide coat get a can of Black Lacquer in a spray can.it sands eas sand paper.........
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Old 03-26-2012, 12:06 PM
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I'm sorry I haven't posted in a while. I had to put the project on hold until the weather got nicer.

Before I went AWOL...

Sanded the whole car to 220 and re primed the whole car with high build again. This was a mistake in my opinion. I was back where I started, with a whole car to sand again and the same solvent trapped pitting that made sanding the car the first time such a drag. I did what uhohjim suggested and mixed some reducer in. This helped the flow, but it still got really chunky towards the end.

this week...

I peeled off the masking tape, and learned an important lesson: don't wait 3 months to remove your masking tape after 2-3 coats of epoxy and 2-3 coats of high-build. the trim is going to have to be removed now for sure and hopefully, it will clean up. Otherwise, I will have to open my wallet for some new ones.

i spent all night sanding yesterday with 180 grit on an 18" longboard. I have a lot of pits to sand out, but the panels are looking pretty straight. I also have some cracks in the primer that need to be fixed. I was planning on sanding into them until I hit the bottom of the crack, then widening the crack slightly and filling it in. any recommendations/suggestions?
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Old 03-26-2012, 12:57 PM
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You need to make sure your panels are straight. You're block sanding it so you're doing it right. after you sand your primer with 180 put another 2-3 coats of high build on there and block sand with 320 and then finish sand with 600 grit before your topcoat. Minimum of 400 grit before you seal it.
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Old 03-26-2012, 01:11 PM
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I really don't want to use the high build again. I'd rather use more epoxy, but I guess if the panels aren't straight I'll have to fill somehow. can I jsut apply the high build where I need to?
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Old 03-26-2012, 01:13 PM
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You can apply high build primer in spots yes, however make sure you fill those 220grit scratches with something before seal/topcoat. Sealer is not supposed to go over anything coarser than 400 grit scratches.
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Old 03-26-2012, 01:20 PM
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thanks for the advice! I was planning on sanding with finer paper, it just seems like I can't get ther. Everytime I spray anything I end up back at the beginning again, and again, and again...

I'm going to remove all of the trim tonight and keep sanding. I'll post some pics tomorrow.
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