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I painted a friends wrecker last September, The front clip is made of fiberglass and had been hit on the driver fender and repaired years ago. I had to do some work on that fender and all looked very good but now there are bubbles on that area only. I used spi sealer, spi black black and spi euro 5000 clear. Any help is very appreciated.


evil painter
Not sure what all you did to repair the fiberglass or how bad it was, but definitely sounds like air bubbles working up from the repair.
Did you start out with resin & matt for repair or was that all previous? Very easy to get bubbles internally & can take years for it to show up sometimes. After first stages of repair extra heat & dry time help the resins to shrink closer to where they will stay & help hidden bubbles to hopefully show themselves.

But moving on now, that's par for the course for fiberglass & it's hard for you to be 100% responsible for what lies beneath. As you of course know, area would need to be stripped. Then picked at for spots coming loose or revealing bubbles. Then it can be filled, much preferably epoxied, plenty of dry time with some extra heat, & then sand & paint.
This of course is not only a lot of time for you, but to do as good as possible, a lot of downtime for a money making vehicle.
May want to explain to friend & see if he can live with it.
The repair is from years ago, I ground out the repair today and they did not use mat, They used resin and filler. I put new mat and resin in and will wait for dry time and then go from there. Do you spray 2k or epoxy over fiberglass mat?
I'm trying to get this right so should I do all the body work including filler then epoxy? I was told by a guy local to me that I should just use 2k primer over everything so I could sand out imperfections, I really appreciate your help with this as I am new to fiberglass.


Trying to be the best me, I can be
2k urethane doesn't like bare fiberglass. Epoxy or poly primer are what you want to put over fiberglass. Urethane will eventually release, which is probably what happened to the repair causing the bubbles. If you need to get it done fast use some poly primer, if you have time use epoxy 1:1.


Trying to be the best me, I can be
Should I epoxy over the fiberglass before using any other fillers over the repair?
No need. Do your filler work and when ready to prime use poly primer if you need it done quickly which it sounds like you do. If you don't have any Poly and need speed do your epoxy 1:1:10% - 1:1:20%. Give it minimum 2-4 hours at 70- 75 degrees. Then if you need too, spray a couple of coats of 2K urethane to fill any scratches etc. But your best bet if you are in a hurry and have to use epoxy is to get your filler as close to perfect as possible, then the epoxy followed by a light sand.
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I really appreciate the help, I'm pretty sure my friend has poly fill that he will give me to use. How long do I need to wait to spray color over poly?
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Trying to be the best me, I can be
Read the TDS of the poly primer you are going to be using. But as a general rule, give poly primer minimum 2 hours @75 degrees. If it is a small area you can help it along with a heat gun (don't get the surface too hot 120-140 max) Then you can sand. Generally once the tackiness is gone it's ready to sand. After sanding you can go directly to paint. If you have some sealer I would seal it, if you don't it's not the end of the world seeing that it's a work truck. If you are not sealing plan on finishing the area with 600-800 wet.