Repairing fiberglass: Untraditional methods?

Anything goes in the world of fiberglass and plastic



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PostPosted: Thu Jul 04, 2019 9:27 am
I don't want to mess with the fiber sheets, but am dealing with old, thin 1/8" thick fiberglass cracks near stress points.

Does anyone know of a chemical which will make cured resin liquid again, then perhaps mix more liquid resin into the solution? I see epoxy, JB Weld, all that kind of stuff. It works "ok" but we all know it sucks for cracks. I don't believe it actually forms a molecular bond to the resin. I am talking something similar to welding. I know some plastic is now welded, plastic is melted and more plastic is deposited (how metal is welded).

I have used a dremel and "V beveled" one of the cracks on the non-visible side, put tape over the crack on the visible side, and then used cutting discs to cut several straight slots across the crack perpendicular to it's propagation, deep enough to obscure pins. I then used a $40 gelcoat repair kit from West Marine and mud spreader to pack all the penetrations. I immediately popped/snapped small steel pins into the perpendicular slots (I'd cut the straight sides of cotter pins that were the same diameter as the slots so they basically "snapped" into the slots) and ran a final coat of gelcoat over them and let it all set. Next day, pulled the tape (packaging tape I use a lot for paint because of the crisp edges) and the visible side the gelcoat had filled the void completely flush to the paint.

This worked, and the crack has not returned. But that kit was expensive, and I do not like the look on the inside. Also, it has not been long. Looking for other ideas that will last.



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PostPosted: Thu Jul 04, 2019 11:42 am
I don't know of anything that is going to liquify cured fiberglass resin. how about some pictures of what your doing? I don't think the jell coat is the structural part of fiberglass lamination. it just to give a smooth colored finish when sprayed into a mold the resin with glass fibers is what gives it strength. I understand using the jell coat to get the color you had.
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PostPosted: Thu Jul 04, 2019 11:55 am
Once liquid epoxy resin has done it's molecular cross linking there is no more "opening" of the cured material. About the best that can be achieved using the stuff is "wet on wet" layering and even that can be somewhat problematic.
Another thing I somewhat challenge now based on archival research I am doing currently is the adding of metal for strengthening in a fiberlgass or epoxy layup. Laminating fibers, ceramic micro-balloons, etc. will give strength without introducing the tendency for "shock loading" because metal is in an area. Another thing is the different co-efficient of expansion between the metal and surrounding plastic IF the area is subjected to heat.
Badsix is correct there as well.... gel coat was originally done to give a "finished" surface to sell "no paint" dune buggies, kit cars, etc. Gel coat is sprayed in up to 20 mils thick first in the mold, then comes the chopper gun, and cloth layups for the strength of the panels.
If you've got thin, fragile glass.....track down more information on that manufacturing layup process and just continue to add more layers on the inside/underneath. I've done this on many, many, kit cars over the years. This method also allows me to chop, saw, move fiberglass as needed and then "lock" it in the new position.
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PostPosted: Thu Jul 04, 2019 12:23 pm
DarrelK wrote:Once liquid epoxy resin has done it's molecular cross linking there is no more "opening" of the cured material. About the best that can be achieved using the stuff is "wet on wet" layering and even that can be somewhat problematic.
Another thing I somewhat challenge now based on archival research I am doing currently is the adding of metal for strengthening in a fiberlgass or epoxy layup. Laminating fibers, ceramic micro-balloons, etc. will give strength without introducing the tendency for "shock loading" because metal is in an area. Another thing is the different co-efficient of expansion between the metal and surrounding plastic IF the area is subjected to heat.
Badsix is correct there as well.... gel coat was originally done to give a "finished" surface to sell "no paint" dune buggies, kit cars, etc. Gel coat is sprayed in up to 20 mils thick first in the mold, then comes the chopper gun, and cloth layups for the strength of the panels.
If you've got thin, fragile glass.....track down more information on that manufacturing layup process and just continue to add more layers on the inside/underneath. I've done this on many, many, kit cars over the years. This method also allows me to chop, saw, move fiberglass as needed and then "lock" it in the new position.


Now THAT pisses me off, because I drove a half hour to West Marine and had a talk with their employee about what I was doing. And he suggested that $40 gelcoat kit. It is holding pretty strong with the pins thus far, but he went as far as telling me there was a chemical bond.

Dicholoromethane will bring fiberglass resin to solution btw. I found this out after posting.



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PostPosted: Thu Jul 04, 2019 12:37 pm
I'm dealing with cracks in painted fiberglass motorcycle parts/trunk. Newer stuff is ABS, this is the old tan stuff. Just trying to make it look uncracked inside and out, not crack again. Id rather not play with the sheeting and resin if I can get away with it.

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PostPosted: Thu Jul 04, 2019 6:09 pm
Who gave you that info. on dichlormethane (methylene chloride)???? It will definitely weaken/melt/dissolve fiberglass but it in no way allows proper bonding of more product to it. The molecular chains are not properly linked..... I was a stripping agent manufacturer for many, many years and I had access to several labs for work with these stripping agents.
Repairing fiberglass can be as simple as using short or long haired fillers. USC's Duraglass is a strong filler, bonding agent for repairing fiberglass.
Metal, wood, fiberglass, we work it all... www.furniturephysicians.com We can restore the irreplaceable!



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PostPosted: Thu Jul 04, 2019 6:59 pm
DarrelK wrote:Who gave you that info. on dichlormethane (methylene chloride)???? It will definitely weaken/melt/dissolve fiberglass but it in no way allows proper bonding of more product to it. The molecular chains are not properly linked..... I was a stripping agent manufacturer for many, many years and I had access to several labs for work with these stripping agents.
Repairing fiberglass can be as simple as using short or long haired fillers. USC's Duraglass is a strong filler, bonding agent for repairing fiberglass.


Thank you! I will have a look at that! I'm just dealing with tiny, hairline cracks in my parts, been brainstorming for ways to figure out a way to melt it back together.

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PostPosted: Fri Jul 05, 2019 8:01 am
That's a tough path to follow....I hang around with fiberglass and plastic guys at our local shows almost every other week all spring, summer, & fall. If there was a faster/better way of eliminating this type of cracking I would have heard about it. Cracks originate from poor designs, bad or insufficient lay up, and just plain old use/abuse. Just trying to "fuse" them back together doesn't begin to address any methodology for stopping them from reappearing. Bevel them, stop drill if needed on the ends, and fill with a good epoxy or polyester base resin/fiber system. I just saw a car that I did that to with 16, 1 to 2 inch cracks at all of the fenders (not enough initial layup). It had been 28 years since I sold it. None of the cracks came back..... Guy that currently owns it wasn't even aware there had been repair in those areas......
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PostPosted: Sat Jul 06, 2019 7:04 am
117329 wrote:
DarrelK wrote:Who gave you that info. on dichlormethane (methylene chloride)???? It will definitely weaken/melt/dissolve fiberglass but it in no way allows proper bonding of more product to it. The molecular chains are not properly linked..... I was a stripping agent manufacturer for many, many years and I had access to several labs for work with these stripping agents.
Repairing fiberglass can be as simple as using short or long haired fillers. USC's Duraglass is a strong filler, bonding agent for repairing fiberglass.


Thank you! I will have a look at that! I'm just dealing with tiny, hairline cracks in my parts, been brainstorming for ways to figure out a way to melt it back together.


I did order the short hair repair product you suggested!

Would the methylene cholride melt what's existing back into "seemingly" one piece if it were wiped on a hairline crack(s)? In a very superficial sense. Could it be used to thin out specific areas (thickness)? I'm just wondering what the actual effect would be. If it acted like muriatic acid, then it would be aggressive and just burn the crap out of everything. Are we talking a reaction like that, or maybe one more like wiping cured paint with paint thinner? Pure curiosity on my part.

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PostPosted: Sat Jul 06, 2019 7:29 am
Well, yes and no....you can easily use meth. chlor. to "melt" the area making it look like the crack is trying to reform, however the fiberglass just doesn't recover like that making the area weaker. And, again, you are not addressing or FIXING what caused the problem in the first place. Most of my experience with this over the years was doing our own research into producing "safer" stripping chemistry for fiberglass as well as some other plastics. Although we were somewhat successful in coming up with formulations that can do this you just can't completely get around the fact that there is some melting/distorting of the fiberglass resin. Then, we usually found out that trying to layer or attach more fiberglass over that just resulting in a peeling delam. We could never compete with just taking razor blades, sandpaper, etc., to do the stripping with much less stress to the fiberglass/plastic surface. Dave White, the former owner of Kwick Kleen over in Indiana had a fiberglass/plastic stripper in his inventory for many years (it was about the best I had ever seen) but sold very little of it.....it's not that it didn't work but people would just tried to be to aggressive with it leaving distorted surfaces......
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