Confusion over primer to base coat times

69Mach

New Member
I am a little confused with the some of the times between primers and color coat, so let me state my thoughts and see what feedback I receive.
I have a 69 Mach 1 and I have replaced virtually every piece of metal except the roof structure and the VIN tag. I am having the base and clear sprayed professionally in a booth,
The metal came in two versions, the black EDP and the silver weld thru primers. The black parts, I cleaned and scuffed with red scotchbrite, and the weld thru, I DA’d with 80 grit. Both got final cleanings with SPI cleaners. The parts are all getting SPI epoxy initially.
My plan was to epoxy, 2k, then epoxy and final sand with 500-600 range paper. Then I was going to jamb and fit the doors, then jamb the fenders and mount them, that way I can transport the body, ready for external paint. The body is stripped and on a frame jig. I wanted to do it this way to make it easier to transport everything and get a good even final paint without worrying about damage during door alignment, etc. I figure at my speed, I will be at the end of August before the body is ready to transport and paint.

Now my questions: I am reading that the 1-2 month delay in painting will effect adhesion between the epoxy primer and base coat. Is this correct? The color is going to be a GM Hyper blue metallic, so it’s a lighter blue? Will this metallic blue require the 500-600 final sand, because I thought I read Barry said you would be lucky to get 400 grit on the primer? Could I wait the 1.5-2 months and let the epoxy harden and then final sand the exterior with 500-600? Would that help the adhesion issue?

If the epoxy is a no go on the 2 month window, my second thought was to final sand the 2k primer with the 500-600 grit and base coat over the 2k. Is that a viable alternative? Will the 2k have a longer window (2 month) to get the base coat sprayed? Is a sealer required or necessary?
On a side note, I have 3 quarts of Slicksand left. My deck lid had some ripples I couldn’t quite get out after welding, and I sprayed it with un-reduced Slicksand thru a 2.5 gun, and it sprayed nice and smooth and I had no issues, so I guess Slicksand is a option for a final coat too.

I am a little out of my element, so I appreciate any advice or concerns. My shop has A/C so I can control the temp pretty well, while spraying.
Thanks, Chris
 
Any final sanding should be done 24hrs or less before application of anything. As Rbm said above. a coat of epoxy reduced as a sealer before base is necessary, for maximum adhesion. I would not spray any complete without sealing first. IMO, any polyester needs some kind of sealer before base. It is porous like filler. Being a lighter blue, any sand scratches will show much more than a dark or solid color. The sealer will help a lot to prevent this, also.
 
Thanks

I really appreciate your advice. I think my plan of action will be the epoxy, then the 2k, then block the car and sand with 400, then spray the jambs and after that, mask the jambs and install the doors and fenders.
Then right before paint I will do a final sand with 600 and then transport to the painter for a final application of reduced epoxy (sealer) and then the base.

Sound about right?

It won’t cause any problems to have the car blocked in 400 for a month or so before transport to the painter?
On the door jambs, do you think a scuffing with red scotchbrite will be sufficient or do the jambs Or will they also need to have the 400-600 treatment? The epoxy on the jambs is looking pretty smooth as it sits.

sorry for so many questions, but you guys are a wealth of knowledge.

Chris.
 
Sanding a month or so before final sand is not ideal, but will be fine with a little extra step. Clean the sanded primer thoroughly with 700 before your final sand, to remove any possible contamination that may have gotten on it. Sanded primer has more area for contaminants to "hide" is the reason.
 
Another factor is some primers "self heal" to some extent. In addition to TK's good advice you can also use a red scotchbrite pad and some sanding paste like "Scuff-Stuff" to clean and scuff it prior to sealer.

On the door jambs, do you think a scuffing with red scotchbrite will be sufficient or do the jambs Or will they also need to have the 400-600 treatment? The epoxy on the jambs is looking pretty smooth as it sits.
It might look smooth but it is not flat. Yes you can scuff it but it's not going to look as good as blocking/sanding it.
 
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