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  1. #1

    repair carbon/kelvar board with fibreglass?

    Hi all,

    Been following this forum for a while, and finally have a question I can't find the answer to, so it mobilised me to finally sign up!

    My question is this - I have a fanatic freewave from 2005 to be repaired. I have experience with boards repairs, but they have all been standard epoxy sandwich boards, and this one is a 'carbon-kelvar' construction. Normally I would use epoxy resin + fibreglass, but I know that ideally one should use the same material as the original so that in the case of the next hit it absorbs the impact better.

    My questions then are:
    1. do I use kelvar instead of fibreglass to fix the damage? Or does it not matter and should I just go ahead with fibreglass? Can you even get kelvar for these kind of repairs?
    2. even though the damage is pretty serious and the deck soft in places around the hit, the shell is quite stiff still (although cracked). Normally I would take off all the cracked bits, sand down and then apply with fibreglass/kelvar, but as I have not worked with carbon/kelvar before maybe I should leave what is there and just put something on top to seal it, and not weaken the board more structurally?

    I hope that makes sense. Attached is a photo of the damage. Thanks for any tips and feedback!
    Click image for larger version. 

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    M
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
    Senior Member chrispavlo's Avatar
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    my recommendation would be to use carbon cloth -
    it is strong and easy to sand

    example where i used carbon on my board:
    Click image for larger version. 

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  3. #3
    It's irrelevant what cloth you use since it is impact damage not stress damage. I would do exactly as you describe above, but also rebuild the sandwich too.
    http://forwards4cowards.blogspot.com/ a blog about looping

    UPDATED Feb 2016

  4. #4
    Senior Member Witchcraft's Avatar
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    It is hard to use Carbon Kevlar for repairs since you can not sand the kevlar smooth. Also just glass fibre is at least as strong and for sure stronger against impact as carbon. So do as you say, sand down the CK in an area of 5cm around, going gradually deeper towards the crack and you see the sandwich. Then you can fill this up with glass fibre. The biggest layer first. And use vacuum if you can or otherwise apply some pressure (as equally as possible) with tape and maybe some soft foam rubber. If you put tape or plastic over the laminate first, it will not stick to it. It may be advicable to put a few glass fibre layers over the whole nose while you are at it. It will likely save future repairs.
    Bouke
    Witchcraft Sailboards Fuerteventura

  5. #5
    Senior Member
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    Quote Originally Posted by floaty_jumper View Post
    2. even though the damage is pretty serious and the deck soft in places around the hit, the shell is quite stiff still (although cracked). Normally I would take off all the cracked bits, sand down and then apply with fibreglass/kelvar, but as I have not worked with carbon/kelvar before maybe I should leave what is there and just put something on top to seal it, and not weaken the board more structurally?
    It's an old board. But it would be good to inject 2k marine urethane foam before laminating.. if the core was intact the deck wouldn't be soft. The foam expands, filling voids and cracks underneath the deck, penetrating into the core, and adheres to pretty much anything. It has quite similar properties to EPS core, and doesn't produce much heat when curing. Trim off the excess and sand back, and laminate with S-glass or carbon. Kevlar won't sand (I've tried) and it won't cut with a razor blade (I've tried.) Carbon will.

  6. #6
    Hi everyone, thanks for all the feedback - that is super helpful, especially the advice on not going with kelvar and just proceeding with fibreglass or carbon, and filling with the urethane foam before. It makes me feel much more confident with this going forward. I'm heading off to Europe in the next few days so should be able to pick up all the supplies needed there and I'll tackle this project when I am back home in August.

    Hopefully the carbon-kelvar on my board will sand better than kelvar does, or it'll be a right pain to get the cracked bits of my board off I'll keep you posted how it goes!

    Happy sailing in the meantime!

    Mik

  7. #7
    Senior Member chrispavlo's Avatar
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    trick for sanding kevlar: coat it with epoxy then sand,
    repeat
    Click image for larger version. 

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    Last edited by chrispavlo; 24th July 2014 at 11:20 AM. Reason: pic

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