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Old 08-30-2007, 02:40 PM
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Sanding the *%^$&# primer all off the fiberglass parts

I don't know if it's newbie errors or a combination of problems, anyway after blocking an filling all of my fiberglass parts and priming them, I noticed some adhesion problems with the primer.

In places I could (if I tried really hard) pick small amounts of epoxy primer from the surface, with my thumbnail.

I didn't think this was good, so I am 1/4 of the way through removing all the primer from the fiberglass parts.

I think the problem has to do with the age of the primer (1 year I have been using the same paint)

It could be a cleaning issue. I dewaxed the parts when I brought them home, but maybe it was a cleaning issue or prep before painting.
a) vaccum
b) air
c) dewaxing / degreasing cleaner
d) air
e) alcohol
f) heated the parts with lamps overnight to evaporate any remaining solvents

I used acetone on the bare metal, which I did not use on the fiberglass, as it acts as a solvent, and may chemically "soften" the glass.

So I am going to let the paint shop do their thing on the fiberglass. It's not going to rust.

Any thoughts on the prep work?
Some of this went on fiberglass with scuffed/sanded gelcoat, other parts were raw fiberglass or filler over glass.

Because the 'glass was in so many different stages of finish, I am kind of thinking that the epoxy primer was just too old and changing chemically. That or not compatible for adhesion with a fiberglass product.

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Old 08-30-2007, 03:09 PM
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fiberglass...........

hi,ive been repairing fiberglass boats for almost 40 years.Acetone will NOT hurt cured fiberglass parts. i wash all fiberglass with acetone on a paper towel,3 times,(change p.t) between washings.then i spray a dust coat of black paint(dye coat) very lighty so i can see where i have not sanded. (black dye coat will stay in imperfections) i sand all fg with 150 grit paper (ui want a good TOOTH for the primer. then wash again with acetone.(very good) then prime with epoxy primer,(usually 3 coats) wait 24 hours,sand with 320 grit. then spray color coat.check for imperfections (WHO ME????) do repair as necessary. spray clear usually 3 coats(more if over flames or stripes) then walk away and leave it alone. i usually wait 2 or 3 days( ALL primer,paint and clear,is 2 part. then check again for imperfections (WHO ME????) do repairs as necessary. then have fun water sanding. (add some dish soap to water) i sometimes use a jitterbug to water sand ,start with whatever grit paper is needed.finish with 1000 or 2000 grit buff and polish.
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Old 08-30-2007, 05:31 PM
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Thanks for the tips
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Old 08-30-2007, 08:50 PM
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c) dewaxing / degreasing cleaner

Ripped, what dewawing/degreasing cleaner did you use? I've seen people try to use household degreasers for this job and have contamination problems so I'm just curious if that might be the problem. I don't see anything in your proceedures that would cause a problem. The epoxy would have stayed soft for days and days if the catylist was bad, if it hardened up the primer was good and your prep was bad.
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Old 08-31-2007, 06:22 AM
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What primer did you use? Was the surface still warm from the heat lamps when you applied it?

Brian
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Old 08-31-2007, 09:07 AM
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The de waxer which I used is called "Plasti-kote" wax and grease remover.

As I am sanding, it appears that some of the primer has excellent adhesion, in fact, probably a lot of it does. I don't want to take any chances though.

The piece I worked on last night had the gel coat pretty much intact (scuffed, light block sanding required only), and the adhesion seems perfect.

The trunk that I started on, had areas (surfaces) which were very bad, to others which were perfect adhesion.

Primer is call "morton" I think, I'll check when I go home tonight.
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Old 09-01-2007, 07:50 PM
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Sounds like the epoxy is just fine, as the epoxy does not know to dry and adhere good in this spot and not in that spot.

Kind of leaves the issue of cleaner and application of cleaner along with application of first coat of epoxy.

Never herd of the cleaner you used, is this a good grade or made up of recycled solvents?
It is almost acting like using thinner to clean metal as you get good adhesion and poor adhesion as thinner is a very poor cleaner.

The above we can not answer unless you made the stuff so next question is when you applied the cleaner I assumed you dried with a clean rag but how long did that set before you epoxied, in other words, it may of looked dry but was it? High humidity will delay the process and that could very well be the problem and my guess.

Was the first coat of epoxy sprayed wet or was some spots sprayed wetter then others. that can make a big adhesion difference.

Last but not least how long has the epoxy set? Epoxy can be scraped off the next day pretty easily but will gain more adhesion as time goes by. Three or four days it should be about impossible to scrape off or peel.
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Old 09-01-2007, 07:56 PM
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need to make shure all of the mold release is gone, or else paint or primer won't stick
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