Fiberglass work and painting

[Jim]

I had to alter a stock Harley side cover.I used half and made the other half from fiberglass.It came out nice and smooth.I primed with Sherwin Williams and painted it with HOK base and clear.(I used epoxy primer on the other parts but needed to do so finishing on the cover and didn't feel like waiting 4 days for it to cure)Looked great until two weeks later when I left it in the sun,then it bubbled under the paint.The stock half looks great but the side I made got soft and bubbled.Does anyone know why this happened?It was hard as a rock until it got hot.It goes over an oil tank so,heat will always be an issue.Just to clearify,the fiberglass bubbled not the paint!Would the epoxy primer stop this from happening again?I'm thinking it's a reducer reaction or something like that but,would like to hear from someone who knows before I tackle this again.

 

[TAZ]

Hello Jim,
My guess would be that you possibly had air pockets in the fiberglass. The reason I say this is because you say when it's near hear, it bubbles.

Epoxy primer will not hold this down. You will need to regrind the areas that contain the air pockets and rework them.

 

[shaunboy]

I WORK WITH ALOT OF NEW FIBREGLASS UTE CANOPIES.
WE ONE HAD ABOUT 5 BUBBLE IN A ROW.
THIS WAS ONLY SMALL BUBBLES BUT ALL OVER THEM
IS WAS IN THE FIBREGLASS GELL COAT THAT WAS NOT FULLY CURED.GELCOAT SHOULD BE LEFT UP TO A WEEK BEFORE APPLYING AND PAINT.
BIG BUBBLES ARE LIKE SCOTT SAID BEING AIR POCKETS.
ANY FIBREGLASS THAT WILL GET HOT MUST BE MADE TO PERFECTION WITH THE RESIN FILLING ALL AIR POCKETS.
ALL FIBREGLASS THAT IS PAINTED IN DARK COLOURS WILL ALSO GET VERY HOT IN THE BRIGHT SUN.

 

[Jim]

I'll bet you guys are right!I remember I could see thu some spots when I held it to the sun.I figured since it was smooth it would be alright,guess I was wrong.Thanks-The rest of my painting and flaming is coming along great.thanks to this great site and all those who reply to our questions.Thanks Guys!

 

[rex]

Jim,that sucks.Use a glass roller as you lay up each coat to push out the bubbles.I use a cheap paintbrush alot but they're tricky to get out the bubbles.I sand or grind my glass low and pop any bubbles I find no matter how small.Then finish off with a skimcoat of mud,but scrape in the initial layer so it fills in the popped air pockets.