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Several years ago, I watched a youtube tutorial about repairing carbon fiber. I can’t find that video now, but one of the first steps, before applying sheets of cabon fiber, the guy used a compound that was a mix of carbon and epoxy applied down inside a crack, where the sheets couldn’t be forced in. It was kind of an extra step just to maximize strength as much as possible. It was a charcoal color, and it was sanded smooth before applying carbon sheets. I can’t figure out what it was called, but I need some. I guess it’s possible the guy made it himself...

Anyone know what it’s called?

  • I'm guessing it was some kind of resin, the stuff that binds the carbon fibre sheets together. – Criggie May 19 '18 at 20:44
  • Don't repair carbon fiber yourself unless you REALLY know what you are doing. "Maximizing" the strength with wrapping etc can just as easily minimize the strength in a different area and lead to very bad things. Sure you might get lucky and not do something that will later lead to serious injury. If you can't afford to replace or get the repair done properly, then don't buy carbon in the first place. Never repair bars, posts, or most rims, even professionally. What's your body worth to you? – Purr May 25 '18 at 22:43
  • I do understand this risk. In this case, the area is non-structural from a safety standpoint, but I want to get as much strength as I can anyways. – BBaysinger May 25 '18 at 22:47
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I found the video, and it turns out my memory was off. It’s a graphite powder mixed with epoxy. He doesn’t explain why he used graphite, but that layer of resin was only to prevent air leakage from inside the tubing during the vacuum stage, and probably also to help the carbon sheets lay flat. Perhaps the graphite was added to make the resin more sandable? In any case, it wasn’t a carbon mixture, and it does not provide strength to the repair.

I would be interested in hearing if anyone has knowledge of such a product.

  • 3
    Good work, thank you for adding the answer for completeness. Generally speaking, none of the regulars have spent a lot of time working with carbon fibre, so the knowledge pool is shallow. I don't personally own one either. If you could please have a browse through bicycles.stackexchange.com/questions/tagged/carbon and add what answers you can. Welcome to the site. – Criggie May 20 '18 at 7:35
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A product that solves the issue I’m confronting is called milled carbon fiber powder, as is available from Easy Composites. I already have the resin, so I can add this product to get more strength from my repair.

I was also searching for “carbon composite resin”, and hoping to find a resin pre-mixed with carbon fiber, but there’s a lot of noise in the results. Not sure if there is a product ideal for this application.

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