An Enamel Painting Question

[pennstump]

You'll have to excuse me, but this is rather lengthy.

The front windscreen from my motorcycle had cracked from my last move, so about 3 weeks ago I decided to fix it. It had a smoke-plastic look to start with, probably a polycarbonate or polypropylene. so, I used super glue, and used it like an epoxy. this filled the crack, and i could even sand it the next day. this made the thing pretty smooth. i used up to 400 grit wet sand paper.

so, now i washed the thing with a no-static car wash and let it dry. then i primered it with a white enamel primer, about 3 coats at 10 minutes apart. the next day i sanded it at 320 grit. then over the period of a week, every other day, i painted a couple coats of a gloss black enamel. each time i would see problems in the paint, so after a day or two i would sand it again to smooth, working up to the 400 grit again. then i'd paint again.

so, after about a week of painting and sanding the thing looked really good. so i let the enamel cure, for close to two weeks curing. so i install it on the bike. I go out on the bike for that day, everything looks good. I then put the vinyl cover back on the bike.

now, 5 days later I go back to get the bike out again.... and the paint is ruined. it's somehow still black, but blotches of it are a non-smooth matte black. it's kind of an amorphous shape.

i don't understand it. i just installed new headlights and they do make more heat than the old ones, but i didn't drive it that first day for more than an hour. there is lots of humidity in the air, would that do it? i checked the inside of the cover, there's no sign of any reaction there, I can't even find paint chips anywhere. why did it do it? where did it go even? did it evaporate? i used an enamel instead of a lacquer or anything else because it's supposed to give a decent shine and be rock hard. i didn't use a clear coat because of all the limitations of painting over enamel, and the fact that clear enamel is supposed to be nasty and hard to use...

What should I do next?

thanks.

 

[ripvan]

it may be that moisture (humidity?) is causing the paint to "blush" but I tend to think that the blotches are coming through the paint...perhaps the thinners or turps is not compatible, or is reacting with some component of your chemical mix?
In either case, it will require sanding back, sealing and start again, but maybe there is a paint shop nearby where you can prove that your mix of components are compatible?

 

[pennstump]

thanks. that explanation sounds the most plausible. i wonder why it happened, though. i used the same brand for the primer and top coat.

Do you think I should try to use the clear coat on my next attempt?

 

[ripvan]

if the blotches are coming through the paint, putting more paint on top won't help.
It may be that the original surface was contaminated by greasy fingers, silicon etc etc.
I'm not a spray painter, so any spraying that I do, I am meticulous in my preparation - it takes the longest and is less rewarding than the final coat, but it is critical.
From where your job is at, *I* would sand it right back, clean with Prepsol (or whatever you equivalent is) seal it (after confirming that the sealer and base material will not react) , prime, undercoat. Let it dry thoroughly, Prepsol again, and then final coats.
If you are using enamel there is no need for clear, but *I* would use acrylic laquer and then finish with clear (for small jobs, the automotive paint spray cans are fine).
Buff it, then polish and voila...no more blotches and perfect job )
It is important to note that not all thinners are compatible. Enamel thinners *will* react with laquer thinners, so cleanliness and the right materials are the keys.
Good luck with it, post again and let us know how you did.