Why you should use a sealer

idk some spots on the hood the clear coat would be smooth but the color looks bubbled underneath
 
I was taught never to seal unless I was ready to spray base within 30 minutes.
 
I normally endup with either trash or something goes wrong so I end up sanding anyway. On new parts like bumpers, fenders and hoods I could see sanding sealing and painting. A light scuff with a scotchbrite pad after sealing would make me feel better but I've been wrong before. I started out with oil base on wood and synthetic enamel, the way I was taught always worked, when I started with bc/cc that was a big change. Sometime its hard to change old ways, but sometimes new ways work just as good or better. I had to learned to spray bc/cc so I guess using a sealer is learnable too.
 
no adhesion with 600 grit scratch?????

I have used H.O.K. metallic base a few times and always final sanded with 400 wet .I never seal.Never had a problem.
 
I have never seen anything like that before!!! What a disaster!! My speculation would be contamination during final wipe down before base coat. Maybe the wrong bottle of cleaner was used. I have seen many brands of 2k sanded with 400 or 600 so many times without adhesion problems without a sealer to rule that out. Something was added to this equation that is unknown?
 
I've seen that on new plastic bumpers that were just washed sanded and primed or sealed without a adhesion promotor but without being their when it was done on this one I'd just be guessing but I'd say you're right some kind of contamination.
 
Probably a contamination issue, may have been a trapped solvent deal from too fast of application, but there's also another scenerio that happens with some 2K urethane primers. Some 2K urethane surfacers need to be topcoated soon after final sanding especially if wetsanded otherwise adhesion is lost, especially if the primer hasn't cured to a complete full cure. You're always just way better off using a sealer whenever possible to tie it all together, epoxy sealer is the best IMO.
 
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