Glass fibre pannier repair now failing

[Freddyfruitba...]

Earlier this year I repaired a cracked pannier by reinforcing the damage inside with glassfibre, then body filler/rattlecan outside - was quite pleased with the result. However, a few months later the crack is now beginning to show through on the outside,and looking inside I can see that the glassfibre is becoming unbonded from the pannier surface - in the photo below, the whole area was translucent where the glassfibre was stuck fast to the substrate, but as you can see there's now a large (and presumably still increasing) opaque area where the bond between the plastic and glassfibre surfaces is broken.

Do we think this is likely to be caused by incompatibility of the resin with the plastic of the pannier? Or small movements in the pannier body causing the bond to break? Just wondering whether it's worth chucking in a couple morre layers of glassfibre on top... in all honesty I'm not going to remove all the old stuff whatever, as that would also mean repeating all the work, including painting, on the outside

https://i.imgur.com/Hqvm7pC.jpg?1
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KC100->CB100N->CB250RS--------->DL650AL2->R1200RS->R1250RS

[colink98]

maybe roughen up the surface with a wire brush prior to applying the fibreglass. give the resin something to stick on too.
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PCX125 (stolen) - CBF600 (current)
Ride it like you stole it.
ride sensible and not like an idiot and you wont get 6 points in one week.

[A100man]

I don't think you used enough layers of matting or 'keyed' the base. Use a sharp knife (mind your fingers !) to cut out teh 'unbonded' bits and rough up the surface - enlarging the repair area as you go. then 3-4 layers of well wetted matting.

Well that's what I'd do.
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[stinkwheel]

If it was me and I wanted to do a good job. I'd take all that stuff off, open the inside of the crack slightly with a knife/burr and briefly flame over the inside of the plastic with a blue blowlamp flame.

I'd then bond the inside of the crack using thickened epoxy fillet. Specifically west systems G-flex thickened with microbaloons to the consistancy of peanut butter. While the g-flex is still damp, I'd lay a patch of bias weave glass fibre over the top of it and wet it out using unthickened epoxy. For belt and braces, once it was dry, I'd scratch up the surface wioth 240 grit paper and lay another sheet of glass fibre over that with the weave at 90 degrees and wet that out too.

I suspect the stuff you've used is chopped mat with polyester resin (you added a small quantity of catalyst yes? and it stinks?) Epoxy is much better for structural repairs. You mix resin and hardener then add substrate. Doesn't stink. Takes a lot longer to harden.

You can (literally) glue a plastic kayak that's been cut in half with a chainsaw back together with G-flex then paddle it.

ABS plastic gunwale after being dropped on a metal bar:
https://lh3.googleusercontent.com/mkQiuu-1s1VWN0YXkdJzR9F-JXeArkX-fRnJlDzZ_2A-IThFmuo4nXKvorNtQ_R7pTC4bv-8Iv3WKrJmsgRGMr7eQcqgmTJMkonKQEGMKxIIYx6ylKEOyQZ0Od0l1lwSvkwK0Kn3Kg=w1163-h872-no

After being repaired using microbaloon thickened G-flex coloured with graphite (for added UV resistance).
https://lh3.googleusercontent.com/VhgmsQ1ansrmZqWh9J-430_JIyoZupu0Ddk4r70LcZ2TnnAExC7i1kSrf307CHJ63EUBvOCVqbSvCruJkrmJKtCBXqhNKZHNgj46wlv91j3PH8BjOk69M-V-brRZ4dfZvqi8hepeNA=w1163-h872-no

It's still good 3 years later.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Riejufixing]

[Grubscrew]

Yep. Rejufixing is correct.
Fibreglass bonding only bonds to fibreglass. As you’ve experienced it temporarily works on plastic, but being incompatible the resin doesn’t remain stuck to the plastic as it goes off and hardens .
US weld is extremely good.
Or try to find the same plastic material and melt it in with a wide soldering iron, then finish off with a body filler designed for plastics.

Oh , and drill a small hole at the end of the crack to stop it spreading further.
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FJR1300/CBR1000F

[A100man]

[Freddyfruitba...]

Oh bollocks bollocks bollocks.
Spent many hours and not an inconsiderable sum on colour-matched rattlecans.... should have come before I started, shouldn't I? Thanks to all for the advice, anyway.
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KC100->CB100N->CB250RS--------->DL650AL2->R1200RS->R1250RS