best auto body filler to use over fiberglass

Anything goes in the world of fiberglass and plastic



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PostPosted: Sun Mar 07, 2010 6:53 pm
i would lke to repair a lot of the to know if evercoat z grip would be a good choice to smooth out the waves/slight imperfections in the fiberglass that i have for my drag race car.i have used the west epoxy to repair and fill the major cracks/imperfections,etc.i do nt think that the filler would be any thicker than 3/16 if that.any help/input would be great.THANKS

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PostPosted: Sun Mar 07, 2010 11:51 pm
they all stick pretty well.

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PostPosted: Sun May 16, 2010 3:08 pm
DAVIDS P40 ideal 4 cracks,you will find this on ebay
fail to prepare ,prepare to fail.

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PostPosted: Sun May 16, 2010 7:29 pm
From what I know,,,You shouldn't put a polyester filler product over a epoxy filler. (This comes from the boating industry)
I could be wrong with this comment,,but you better check.
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PostPosted: Sun May 16, 2010 11:23 pm
ODG I think you're referring to no polyester resins over epoxy filler although with boating what you said is probably right. Sun, salt, moisture, yeah I could see that causing problems. I've used Z Grip over the West Systems Epoxy many times over the years. I would however caution you to make sure the epoxy has had time to set and cure up for awhile.
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PostPosted: Sun Oct 03, 2010 10:47 am
i dont think the op even said anything about putting resin over anything he just said filler for imperfections waves then said what resin he was goin to use for cracks i think its safe to say its common sense that u would never put resin over filler.



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PostPosted: Mon Oct 11, 2010 1:33 am
OldDupontGuy wrote:From what I know,,,You shouldn't put a polyester filler product over a epoxy filler. (This comes from the boating industry)
I could be wrong with this comment,,but you better check.


Never use epoxy over polyester or visa versa.... they just won't stick to each other. I use epoxy, fiberglass, polyester, vinylester, gel coats, bondo, clear coat almost every day and trust me i have learned what will and won't stick and even if it sticks and looks good at first... time will probably seperate the two.

If you have a fiberglass part that was laid up with epoxy resin - use thickened epoxy to repair scratches or laminating epoxy to reglass the repair area. If your car body or part is fiberglass mat then epoxy was not used to manufacture the part. Reason is epoxy won't break up the binding agent of fiberglass mat... only polyester or vinyl ester resin will work with fiberglass mat.

How to make your own epoxy filler compound:
1) get your fillers ready.
a. Different fillers available.
1. fumed silica ( works excellent as an epoxy thickener and sands to shape)
2. calcium carbonate ( hard as a rock to sand and shape ).
3. cotton flock ( not for bodywork really... more for boat repairs or rough filling a hole then topping the hole with a finer compound).
4. milled or chopped glass fibers ( 1/16" chopped glass fibers work well for filling detail areas )
5. phenolic spheres or glass spheres ( excellent thickener and easy sanding )
6. talc ( add it for better sandability.... mix in some fumed silica also for thickening )
7. wood flour ( never used it )
These fillers can be purchased at www.fiberglasssupply.com and some other composite suppliers.

2) mix your epoxy for 2 to 4 minutes and don't whip air into the mix so stir slowly and scrape the bottom and sides of your cup for a thourough mix.
3) add fillers, mix to the consistancy of that between pudding and peanut butter... too thick and it won't work... too thin and it runs off.

If you need a lot of filler buy your fillers by the gallon or larger size and don't buy it from West Systems because they rip you off big time. I buy a gallon of fumed silica for $8.. a quart of milled glass for $5, a gallon of glass spheres for $8. West systems makes great epoxy but it is overpriced imo. I would buy epoxy resin from Resin Services or buy Adtech epoxy resin if using epoxy. Epoxy is bought according to it's properties.. there are hundreds of epoxies out there but there may only be 5 or 10 that are suited for your particular use.

Also if you run out of bondo or need just a small amount of filler you can mix up polyester resin and fillers, then catylize by around 5%. catylist isn't real precise just use enough but not too much mekp. I wouldn't use BPO for this. you could also do this if you need a thin flowable filler... just mix accordingly. I still prefer premade bodyfillers if working on fiberglass repair. and nothing really beats the premade stuff... unless you need an epoxy filler.



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PostPosted: Mon Nov 01, 2010 10:32 pm
Upside wrote:
OldDupontGuy wrote:From what I know,,,You shouldn't put a polyester filler product over a epoxy filler. (This comes from the boating industry)
I could be wrong with this comment,,but you better check.


Never use epoxy over polyester or visa versa.... they just won't stick to each other. I use epoxy, fiberglass, polyester, vinylester, gel coats, bondo, clear coat almost every day and trust me i have learned what will and won't stick and even if it sticks and looks good at first... time will probably seperate the two.

I don't mean to be rude or anything, but just because you use something every day, doesn't mean you know what you're talking about, because if you can't get epoxy to stick to polyester, you obviously don't know how to use the products.
Yes, polyester resin isn't recommended over epoxy because as some epoxy resins cure, a waxy layer (amine blush) forms on the surface, which prevents polyester resins from bonding well with it.
Most fiberglass boats are made with polyester resin and lots of repairs are done with epoxy resins. Actually in some cases it's preferred because it provides a stronger bond to the original polyester resin and is stronger.

My answer to the original poster, although I assume he's already decided what to do is, grind the top layer off the cured epoxy to get rid of the amine blush and use any autobody filler.

I don't like to answer questions sometimes because often there are several ways to do something, but in this case, the info about not using epoxy over polyester posted in the quote is absolutely wrong.



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PostPosted: Sun Nov 14, 2010 3:39 pm
hi, i just got around to getting on this forum again.thanks for the replies.this fiberglass race car body that i have been working on for the last few years has been an off and on project.i have repaired a few places on this body with polyester resin, then i read that it was not good to use poly if the body was made with epoxy resin.i called the mfg and they do not rember what resin was used.so i am using the west systems epoxy resin.i am going to use the resin for any pin holes and slight waves but i am still will have to use body filler.i do not think that the filler would be any thicker than 1/8 if that thick.i was then going to epoxy prime the body and use a filling 2part primer.i will probably let the primer set for a few days then block sand and paint.the color will be black and i want it as close to perfect as i can get it!! so at the moment i still have more work to do on this body and drag race chassis,etc. THANKS gary m

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