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primer bubbling/popping off raw fiberglass

 
Old 04-09-2019, 06:28 PM
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Lyndwood
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Default primer bubbling/popping off raw fiberglass

I was working on my t-tops one of which had more than 1/4 o the paint totally gone for lord knows how long, there was no paint there it had flaked off and sun baked the area. anyway I sanded the panel and prepped it for epoxy paint for my base and the top turned out awesome till it dried and now I have what looks like solvent pops in that corner, in the primer. so I presume there is something in the fiberglass that has contaminated it and it's causing that. my question is how to get rid of it, once I sand that area down again back to the fiberglass can I treat or soak that area with something to get what ever is in there out? or is there a way to encapsulate that fiberglass, maybe with VPA to cover it. any suggestions?
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Old 04-09-2019, 08:36 PM
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derekd8915
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When you say encapsulate “that fiberglass” was there raw fiberglass(I don’t mean exposed fiberglass, I mean dry raw fiberglass) on the part when you finished prepping? If so that epoxy primer is not going saturate the raw glass. Should be “hot coated” with resin by brush or roller first. I would of rolled a coat of “laminating” epoxy on all the raw fiberglass until it is saturated and sprayed epoxy primer right over it.
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Old 04-10-2019, 07:04 AM
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Lyndwood
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The glass area was smooth amd whitish grey color, so I'm guessing primer? But it was definitely dry and weathered from being exposed. When I initially hit it with the DA it came off with no effort and I exposed the glass substrate almost immediately. So your saying I should strip it back to the glass base and coat it with resin, let dry, sand and recover with epoxy in that area?

Last edited by Lyndwood; 04-10-2019 at 07:05 AM.
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Old 04-10-2019, 08:08 AM
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csherman
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Solvent pop or fish eye or something else?
All three are different problems

I would completely sand the tops back down to glass.
make sure they are clean and free of all paint / primer
180 grit or 220 grit
Prime them with a polyester primer
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Old 04-10-2019, 09:02 AM
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IF the area on your T-top ...where these small bubbles occurred is where the T-top had already had the paint hope and was exposed to stuff getting on it.

Then there is a chance that something got into the open fibers. Not knowing how badly damaged the exposed areas was before you began to prep it. And if the panel was allowed to dry in the sun or be out under heat lamps to dry it out or draw out whatever may have gotten into it.

Sometimes very long exposure to the outside can cause SMC to lose its top layer and expose the fibers allowing it to glisten in the sun. SO....not knowing if that was the case or not...hard to say any more on that.

What year is the car you are working on???? I assume it is at least a 1971 or later.

Not knowing how much epoxy you shot on it or if in this area you actually double coated it by accident...it is hard to say.

Are the bubbles in the EXACT...and I mean EXACT same area where the top was already free from paint and raw SMC?????

I can say from experience......that once SMC has been allowed to have something get in it. THAT contaminant MUST be taken out and fresh mat and resin applied so further delamination of any top coat does not occur from out gassing.

Sometimes that contaminant does not show any signs of discoloring the SMC in any way.

So...you can try it again due to not knowing how thick you applied the epoxy due to it is realty not designed to be a 'filling primer'.....and is more of an intercoat for added adhesion.... and then apply polyester primer which should aid in keeping this area under control BUT that is still no guarantee due to I have been bit by that method also and had to get back into a fresh paint job and repair the bubbled area by removing the SMC and laminating in fresh material to stop it.

Keep in mind no one here has the crystal ball to see into the future....so...if in doubt...and you do not want to do it all over again WHEN the car had been painted.....which makes it even worse...fix it now.....or take your chances.

Simply brushing a coat of resin on it will more than likely not have enough strength in that layer of resin to hold down any potential out gassing from under it. Like I wrote...I do not have the crystal ball so maybe it would work. It depends on the tensile strength of the resin and how well it bites into the roughed up SMC and if the out gassing is great enough to cause it to lift.

DUB

Last edited by DUB; 04-10-2019 at 09:03 AM.
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Old 04-10-2019, 12:13 PM
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Lyndwood
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it's a 74 dub, the area in question is were the paint flaked off at one point years ago . You could not see base material or fibers, it was smooth and looked like sun baked primer (faded) when I sanded it , it came off instantly with no pressure. It was flaked off already when I got the car 3 years ago so God only knows how long it sat like that or if it was in a garage or outside, probably outside? Maybe it was wax that I didn't get off with cleaner before & I sand it into the base material? Looks like a cross between fish eyes and pops.

Last edited by Lyndwood; 04-10-2019 at 05:31 PM.
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Old 04-11-2019, 06:46 PM
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I forgot to ask, do you oil your tools? Tools I use for for paint prep I NEVER oil, my da is a dynabrade and I use a husky angle grinder that has a lifetime warranty. I know it sounds crazy, But you could very easily get tool oil on a part that will not come off with some cleaners, I would rather be safe than sorry, but this is only my opinion and you can choose to do as you wish.
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Old 04-11-2019, 07:39 PM
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Ironically I was thinking along the same lines in that I was using a die grinde r with a wire wheel on it to remove old weather strip adhesive on the other side if the panel just prior to sanding the top. It got messy too so that maybe the culprit too (adhesive or oil from the exhaust).
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Old 04-12-2019, 10:39 AM
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Fisheyes... as you know create craters. Solvent pop... as you know creates bubbles. So do you have both???

So oil on a panel will not generally create bubbles due to if the oil is bad enough...it will fisheye.

Now knowing by your description that the primer that was on the car came off really fast and easy. I am wondering how well the surface of the SMC did when you sanded it. If it also powdered away you can have an issue of bad SMC and it may need to be ground down and fresh material of good thickness added back on it.

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Old 04-12-2019, 11:09 AM
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Dub do you use evercoat smc resin? Couldn’t figure out why they claim their polyester resin bonds to smc, then found a thread with a letter explaining it from evercoat. They put Methyl Methacrylate in it which can technically chemical bond itself to polyester, epoxy, and metal. Wondering if you had any hands on experience with this and what you thought about it before I order some for testing, or is just a small amount they put in there for marketing.
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Old 04-12-2019, 11:14 AM
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“The reason that SMC Resin work on SMC panels where regular polyester resin won’t is because SMC resin contains a small amount of Methyl Methacrylate (MMA) that help to increase the bond. The MMA works to compensate for the mold release that is in the SMC panel. SMC stands for Sheet Molded Compound/Composite.

In order for the material to be molded it is placed inside of the mold which has a positive and negative side. The material is compressed between theses two sides during the manufacturing process. After the part is cured the positive and negative molds are separated and the part is removed. In order for these parts to come out of the mold a release agent is incorporate into the resin that allows the parts to easily removed, otherwise they would stick to the molds. It’s this release agent that causes the issue for traditional polyester resins to not stick”

https://www.corvetteforum.com/forums...smc-resin.html

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Old 04-13-2019, 08:51 AM
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Originally Posted by derekd8915 View Post
Dub do you use evercoat smc resin? Couldn’t figure out why they claim their polyester resin bonds to smc, then found a thread with a letter explaining it from evercoat. They put Methyl Methacrylate in it which can technically chemical bond itself to polyester, epoxy, and metal. Wondering if you had any hands on experience with this and what you thought about it before I order some for testing, or is just a small amount they put in there for marketing.
I have tried and tried NUMEROUS times to get the EVERCOAT SMC RESIN to bond and work and only have had failures in it.

YES....I also talked with the tech line at EVERCOAT and followed their instructions to the letter. I have used it on numerous C4's only to have it literally pop right off the PROPERLY prepped panel. It did not do it every time...but if it does it once....that is enough for me. And it did it more than on one occasion. SO...I do not use it and use only WEST SYSTEMS epoxy resin when dealing with SMC.

I DO KNOW that Vette Panel Adhesive WILL bond on top of SMC panels.

This EVERCOAT SMC RESIN is one I do not endorse. And I have not tried it since and do not know if it has been reformulated. I am a bit gun shy due to the problems it has caused me and using the WEST SYSTEMS resin has not failed once.

Now I did use up what I had left of the EVERCOAT SMC RESIN to make parts and it did wonderfully there.

DUB

Last edited by DUB; 04-13-2019 at 08:53 AM.
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Old 04-13-2019, 10:49 AM
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is the problem area on the rear outside of the top ?
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