Delay between sanding high-build primer and applying sealer -- bare metal

[derekf]

I finished the sanding of the high-build primer (U-Pol System 20, if it matters). There are places where I've burned through to bare metal, and I won't be in a position to paint the car for another week or two.

The sealer I've got for it is SPI's 2K Urethane Sealer. Directions for the sealer indicate shoot 10 minutes to 4 hours before color and any longer will require sanding before paint.

I had seen somewhere on their forums a suggestion that one never, ever, ever apply anything from an aerosol can to something you want a good paint job on, but one of the youtube paint guys I watch hits bare metal spots with rattle-can self-etching primer.

Given that it's humid in north Texas at this time of year, it seems like the options are:


Use the rattle can self-etching primer on the bare metal spots (how visible are the edges of the etch-primed area?)
Shoot the sealer now and just plan on sanding it (I assume 400 again?) come paint time
Leave it bare, expect to have to re-sand the bare metal spots to clean up any new surface rust
Rush to get to a position where I can shoot the actual paint (this seems like a bad idea)


Or is there another option that I've missed? The paint going on is black (also SPI, with their Euro Clear), if that makes a difference.

[dhutton]

If you sanded through to bare metal it might mean you have high spots in your metal etc. If that is the case your car may not be ready for paint and my need another round of primer and blocking. Maybe post some pics of the bare spots. Black requires dead straight body work which I’m sure you know. I typically do at least two rounds of blocking on a black car, sometimes three.

I use reduced SPI epoxy for my sealer so never any concerns about a sliver of bare metal. If you have any SPI epoxy left I would use that on the bare spots.

Curious how many coats of clear you are planning to apply.

Here’s some black cars I have done.

Don

[derekf]

Thanks Don, I hadn't actually thought about that as a possible route.

Both door handles (suspect this is just me sanding too aggressively in that area)

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Front of hood (possible this was from sanding some glaze a little further back from there. This would be easy to recoat and re-sand, the hood's got natural divisions so I'm not having to redo everything)
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High on passenger rear quarter (this will actually get covered by the tonneau cover, but I think I'm seeing rust starting to form here already)
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Tailgate center
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My epoxy was the Summit branded epoxy so I don't have the "correct" reducer for that.

This is the second round of the high-build primer. First one I only sanded to 220 before deciding I needed more.

[dhutton]

I think most of those you will be ok but I would do one more round on that hood.

Any brand of urethane reducer would be ok for the epoxy. Reduce it 25 to 50%.

Don

[derekf]

Better news than I was expecting.

Would you use the Summit epoxy rather than the SPI Sealer in this case?

[dhutton]

I have no direct experience with Summit epoxy. I am an SPI epoxy user. If it were me I would cover the bare spots with epoxy and then use the SPI sealer.

Don

[dhutton]

Nice thing about black is it’s a solid color so you can panel paint and redo panels if needed. Metallics are not quite so easy.

Don