Clear coat repair - do I need to prime fiberglass first

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PostPosted: Wed Jun 19, 2019 7:49 am
I am repainting a 3ft x 10ft section over the windshield on my motor coach where the clear coat is peeling. I sanded the peeling clear coat off (along with some of the base coat) and feathered the edges. My last sanding step was at 600 grit.

The factory paint is 3-M Diamont. I have purchased a pint of base and the clear along with their reducer and hardener.

My question is whether or not I need to prime the fiberglass now.

I have sanded a few places down to the underlying gel coat but in most places I'm just down to the original base coat.
Some people have said it is fine to spray my base coat directly onto the surface I am at now - others say I should prime first?

I do have some 2K Eastwood AeroSpray Urethane Primer Surfacer (rattle can) I could use.

I would rather not buy the 3-M urethane primer (DP20 2K Urethane) as I would have to buy a gallon with their hardener and it's expensive, and I would never use it all.

What do you think?

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PostPosted: Wed Jun 19, 2019 4:57 pm
Yes, you must prime that repaired area, extending the primer to a bit beyond your repair.

I'd go a bit coarser at P400 under the primer.

The 2K rattle can stuff will be ok but will likely need more sanding before base and I'd question whether a single can would be enough for an area that size.

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PostPosted: Thu Jun 20, 2019 9:46 am
Thank you for your reply.

I will order the BASF/3-M DP20 2K Urethane Primer-Surfacer. I just need to find a supplier now.

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