Introduction: Repairing a Carbon Fiber Bicycle Frame

Picture of Repairing a Carbon Fiber Bicycle Frame

One fine morning I was riding up the mountain and I guess I was pedaling too hard or something.

Somehow — and we're not precisely sure of the precise sequence of events — it seems that I managed to break the bike chain. The broken chain then got itself entangled in the rear derailleur. Since I was still pedaling, fairly hard, this caused the rear derailleur to be ripped from the frame.

All of this happened within the space of about a second. The next second would be even more exciting.

Since I was still pedaling, and the chain was still on the front chainring, the derailleur was then dragged through the narrow space between the rear wheel and the right-side seatstay. Since this part of the frame is a crispy brittle carbon fiber tube, the derailleur managed to take a nice chunk of tube with it as it went sailing past.

This is an interesting bit of damage. I'd never seen it before and although the bike, after a bit of chain tool activity, was still seemingly ridable, it was difficult to know exactly how dire a problem it was. Unlike steel which will bend considerably, carbon fiber tends to fail all at once and catastrophically. So it's a safe conclusion that this is a big problem.

The internet wasn't terribly helpful. Apparently, this is not an uncommon thing. There's a company outside of Santa Cruz called Calfee Design which seems to do almost all the repair work for everybody and everybody seems to recommend their work. Sadly, their work starts at a $300 minimum, requires the entire frame to be stripped down and shipped, and they don't make any particular guarantees.

The first bikeshop people I talked to were anxious to sell me a new bike. A friend who knows a thing or two about frames said to chuck it and buy a new frame. Trek, the company who made the frame with the brittle part right there in the derailleur flight path, would happily sell me a new frame through their "crash replacement" program which borders on a complete scam and briefly made me hate them.

Things weren't looking good.

Then I ran into James at the Missing Link bike shop in Berkeley. While everyone else had been pessimistic and dour, James was brim full of gung ho. And while he had no actual personal experience in this department, he knew someone who had heard of someone who had done it himself.

Good enough! This was precisely the encouragement I needed. So I rolled the bike home and set about figuring out what I'd need.

The entire project took three days, almost all of that spent waiting for stuff to dry. Materials mostly came from TAP Plastics, a local chain selling all kinds of fascinating and deadly polymers. There's a large selection of cheaper alternatives on the internet but I wanted to get this done in a hurry. You probably have a similar place in your nearest large urbanization.

What follows is a set of photos and notes on the process. I hope this is helpful. As far as whether this is a safe or effective way to repair a frame, you're on your own. Seek the advice of a qualified professional. I am neither.

Step 1:

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Note the hipster single-speed setup. After the violent detachment of the derailleur, this got me back home. Also note: hole about six inches up the right seatstay.

Step 2:

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Perhaps the only advantage to having 24 spokes on the rear wheel is that there’s all that space where the derailleur was able to slip through, preventing even more damage. And no spokes broken.

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A better look at the hole. At this point, it’s hard to tell how extensive the damage is.

Still, looks pretty bad. Why on earth you’d design a bike frame with a crispy, nominally irreparable component right here in the line of fire is beyond me.

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Here’s the damaged derailleur hanger. Intentionally made of softer material than the frame or the derailleur itself. When the chain broke and got wrapped around the (now missing) derailleur, it pulled very hard. This broken piece is designed to break off before a chunk of the frame or the derailleur break. You can see the little allen bolt where the broken piece can be removed and a new one put on. They're not terribly cheap (about $20) but far less expensive than a frame.

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There appears to be some damage to the inside, wheelside surface, though it seems mostly superficial.

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So let's get started. The plan is to sand off the clearcoat around the damage, fill the hole, and then wrap a few more layers of carbon fiber and epoxy around the tube in order to, hopefully, return it to serviceable strength.

First, I taped off about a six-inch segment of the seatstay around the damage, and began sanding.

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Tools at this point are sandpaper and fingers. I started with some 220 grit paper, being a little gunshy at first, but that was working real slowly so pretty soon I went at it with some coarser 110.

Here it is sanded down to the fiber level. You know when you get to this point because the sanding dust turns dark grey rather than white.

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Once all the loose crap is sanded away, the hole is smaller than I thought. And there doesn’t appear to be any obvious cracking of the tube beyond the perimeter of the hole.

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Now to start patching the hole. The idea is to fill it with epoxy, let that cure, and then sand down to a smooth surface which will then be wrapped in fiber.

The epoxy and filler come from a local epoxy and filler shop. There is infinitely more of each than I'm ever going to possibly use but these are the minimum quantities available. Total cost was a little under $50.

What we're looking at is a large round bottle of marine-grade epoxy resin, a small round jar of "cab-o-sil" filler, and a smaller rectangularish bottle of epoxy hardener. Epoxy resin is a magic liquid that stays liquid indefinitely. Until you pour some of that hardener liquid into it. Which starts a crazy exothermic (ie, gives off a lot of heat) reaction that quickly results in a hard, solidified resinous mass. The speed of the reaction is determined by the types and amounts of epoxy resin and hardener used. Generally, the slower the hardening, the stronger the eventual bonds. 

There are trade-offs to be made in the choice of epoxy resin. Some are stronger than others. Some dry clearer (as opposed to browner/yellower). For this job, I wanted the strongest I could find. But I also wanted as colorless an end-product as possible (because I was attempting not just a mechanical repair, but an aesthetic one as well). I ended up looking through the catalog (where these qualities are listed) and picking a resin that seemed to be good enough in each department.

And this "cab-o-sil", what is it?  The label says "fumed silica". A white fibery powderous substance that is probably hell on a lung. Make sure you're wearing a dust mask. It's here to give the epoxy some body so that it can be stuffed into the hole and stay there. The other option would have been microspheres. Which are these tiny, bigger than dust but not much, hollow glass bubbles that do roughly the same thing. The difference seems to be that the bubbles produce a much lighter solid while the silica produces something a little stronger. Proper tradeoff? I don't know. The internet sez microspheres, the plastic shop guy sez cab-o-sil, and the price is the same. Since we're talking milligrams here, I go for the silica.

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At this point the plan is to goop a healthy amount of goop into the hole and past the hole into the tube. Let it harden and then sand it down smooth. In theory, this should give the new fiber a smooth surface to bind to. And should stabilize the ragged edge of the damage.

Is this the right approach? It seems like it but often these things have a way of being completely counterintuitive. It could be that by loading the tube at this point with a stiff epoxy will concentrate stresses at some other point, simply moving the failure to a different part of the tube. Or maybe not.

Plus it's hard or impossible to tell what stresses and strains this particular tube sees in action. I'll bet there's a mechanical engineer with a masters degree in exactly this but that mechanical engineer is not me.

Working out the physics of a static load on a bike frame isn't too difficult. But where's the fun in a static load? Once it starts moving everything gets awfully complicated. And all of the obvious simplifying assumptions (the chain pulls the center of the rear axle, the rider's weight is always on the pedals, the bottom bracket isn't flexing in three axes, the road is smooth, etcetcetera) all of them seem likely to also be wrongifying assumptions.

So I tape off everything around the hole.

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The closer the tape, the easier this is going to be to sand down after it cures.

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The epoxy is mixed 4:1 with the hardner and then I added the filler. Enough to get it to about a peanutbutter consistency. Once mixed, there's oh maybe 15 minutes before it heats up and solidifies. Which seems like it should be plenty of time but almost never is.

This is hundreds of times more glop than I'm going to need. But it's fairly difficult to mix up small amounts of epoxy with any accuracy. And if you get the proportions wrong you end up with a sticky, non-hardening mess that's a huge bother to wipe off and start over.

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I glopped on enough to fill the hole and fill the tube extending maybe 1/2 inch in each direction from the hole (that is, when the epoxy hardens the tube will have roughly a one-inch-long solid plug inside centered on the damaged hole). Again, is this the right thing? Maybe I should attempt to fill the tube even further around the hole? It seems like that would make it stronger. But then, there are lots of ways that I could imagine that also weakening the tube. So I compromised.

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The next day it's solid. Now to peel off the blue tape and sand it down.

It turns out that peeling off epoxied blue tape is not particularly easy and I've got to sand off a lot of the epoxy from the tape first. So the order of operations becomes sand, peel, sand.

Lesson: next time, be even less sloppy with the epoxy.

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Once sanded, it looks pretty nice. There's a strong temptation to stop right here.

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I could shine things up and craigslist the bike right now and who would be the wiser? But that would be cheating.

Step 17:

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Here's the carbon fiber. It's about $45 per yard but the epoxy shop guy was willing to sell me one foot for $15. Which is still about 20 times more than I need.

This stuff frays like mad at the edges and that's a bit worrying. I have no real idea how to cut it but scissors seem to work.

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The shape of the tube that I'm repairing is pretty space-age. So a simple rectangle isn't going to work. I made a little template out of paper.

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How many layers of fiber should I use for the repair? No clue. Numbers like four and five seem to get tossed around on the internets when people talk about making airfoils and things.

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So I replicate the template four times.

What's happening here is I'm going to cut out a piece of fabric that's the same complex shape as that white cardboard template. The fabric is going to be soaked in epoxy and then wrapped four times around the frame tube, covering the hole. 

Step 21:

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Masking off everything on the bike you don't want to get epoxy on is crucial. In retrospect, this is far too little masking. The epoxy is going to go everywhere.

Time spent with plastic and tape at this point will pay off handsomely tomorrow. This paragraph has been brought to you by the voice of experience.

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I'm going to wrap a single piece around the tube and I have this theory that each sucessive wrap should be a little narrower than the one below it. The idea is that then there won't be an abrupt change in thickness at the edge of the repair. So note how I've modified the shape of the fabric from the original template: it tapers a bit to the left. The right edge is going to be attached to the frame tube first and then wrap around four times, ending with that narrower edge on the left.

[Edit: note the comment below where it is suggested that this wide-to-narrow wrapping is precisely backwards and that I should have started with the narrow edge first. I believe that's probably the right way to do it.]

This will turn out to not be strictly necessary — it sands down pretty nicely — but I'd do it this way next time too.

Step 23:

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Bike upsidedown is not the best position in which to be doing this. Lay the bike on its side, broken side up. The problem is that the epoxy-soaked fabric will want to follow gravity downward. At least until it starts to set up and gets a bit tacky. But then that only leaves you a couple of minutes where it's still workable.

At the time this didn't occur to me, so watch as I do it wrong.

(This is the point in the process where you go visit the bathroom, have a little snack, relax for a bit. When you come back the epoxy's going be prepared and the next hour is time- and attention- critical.)

Step 24:

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I again mixed up far more epoxy than I needed. The paint brush was used to wet the entire sanded portion of the tube. The fabric was laid out on a disposable surface and a healthy amount of epoxy poured over it.

To spread the epoxy over the fabric I needed a roller of some kind. The local horrible Michael's Craft Store seemed like a place to find this roller of some kind. I've been fooled that way before. What a disasterous place, it's 60% dried flower arranging, 35% scrapbooking (!) supplies, and then an assortment of random art supplies and other garbage. But today I was in luck. One of those random other things was a toy rolling pin for fifty cents.

The epoxy is glopped on and then spread out with the roller. You don't need to use a silly toy; a dowel or an empty beer bottle would also work. However, anything you use will never be able to be used for anything else ever again. So use something disposable.

This is also a good time to talk about ventilation. At this point in the process, the epoxy is giving off clouds of god-knows-what kind of volatile poisonous gasses. You should endeavour as much as possible to avoid breathing these vapours. Open windows, a gentle breeze, and a respirator rated for organic solvents are all good friends to have while working.

Step 25:

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There are no photographs of the fabric wrapping maneuver because I was pretty busy and covered with epoxy while that was going on. However, it went about exacly as expected after the initial scare where the fabric kept sliding off. You start with one edge of the fabric attached to the frame tube and begin wrapping it, as carefully and neatly as possible. Keep the tension snug, avoid folds and creases, don't let your mind wander. 

Once the fabric is in place, the next thing is to cover it with another tight wrapping while it cures. The material of choice for this seems to be black electrical tape wrapped so that the sticky side is out.

Something to be careful of here, which I was not, is to wrap the tape in the same direction as the fabric was wrapped. What you're seeing here, though you can't see it, is the tape being wrapped in the opposite direction. This has the misfeature of causing the fabric wrapping to loosen if you're not excessively careful. It eventually came out alright, so maybe not a major issue, but save yourself some worry and do everything in the same direction.

Step 26:

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Lots and lots of epoxy will ooze out while the tape is being wrapped. A giant mess! Wear gloves and remember to have already masked off everything you don't want epoxy on. Because once it is on, it's not coming off.

Once complete, I took a pin and poked a few dozen holes in the tape so that more could leak out. Lots did.

Step 27:

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There are some stray fibers left hanging out. At this point I'm not sure what sort of problem that's going to be, if at all.

The loop of blue tape on the non-damaged tube is there at the corresponding location of the hole. This way, once it's all sealed up I'll have some idea where the damage was.

Step 28:

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Next day, everything's nice and hard again.

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The tape peels off nice and easy. There's a bit of a spiral but that should sand off easily. I hope.

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Yep, just a light sanding with some 220 grit and it's starting to look interesting.

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Inside done, now for the outside.

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When I said I mixed up too much epoxy, this is what I meant. But it cures to a really nice amber color. Next time I'll find some dead bees first and stick them in the extra before it hardens.

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Once it's sanded, it's looking good. But the fabric pattern is all wonky. It probably would look ok left like this but I decided to go for one more, this time carefully wrapped, layer.

Still, there's now no longer any sign of the original injury.

Step 34:

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Out comes the template again.

This time we're putting on the top, outer layer which will be visible for the rest of the life of the bike. So I have to be careful to get the weave pattern in the fabric to match the direction of the weave pattern in the original fiber of the frame. Carbon fiber fabric seems to come in a large variety of weaves and matching the precise sizes of warp and weft and pattern and texture did not seem easily possible. But we can still come fairly close. And at least match the direction of the weave. 

So look carefully at the non-damaged part of your bike. Is the weave squarely with the axis of the tube? Or is it at a diagonal? Try to cut this last piece of fabric out so that the weave will match when wrapped around the tube.

(If you don't get this exactly right, it's not a terribly big deal. From more than a couple of feet away, the patterns are invisible to the casual observer.)

Step 35:

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This is all happening the day after the initial fabric wrap, so I need to mix up even more excess epoxy. This time I tried hard to keep it under control.

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Also, I laid the bike on its side this time.

Step 37:

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The epoxy soaked fabric is wrapped around the tube, very very carefully and trying to match the pattern in the new fabric as closely as possible to the pattern on the original frame tube.

The seam is on the inside, wheelside, where it will be less visible Then it's all wrapped with tape as before.

Step 38:

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Pinholes again. Gloves are important. You will be very happy if you do this with gloves on.

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More oozy everywhere.

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Hey, next day it's looking very nice!

Step 41:

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More light sanding. Followed by some heavier sanding to get the shape right.

Five layers definitely adds some bulk. Though not as much as I was expecting. Five layers of dry carbon fiber is pretty thick but once it's soaked in epoxy and compressed, it's thinner than I thought it would be.

Step 42:

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Painting time. The spray booth and turntable are probably overkill but I happend to have them around. You could do this in any clean, well-ventilated space.

Step 43:

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Again, mask off EVERYTHING. You will have learned your lesson by now.

Step 44:

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Time to put a glossy coat over the repair to match the original frame topcoat. I'm not sure what's the right thing to use here. Probably the original clearcoat is some sort of catalyzed unobtainium from a country with very different air quality regulations. Next best thing's probably a rattle can from the hardware store. I don't think I'll be needing the rust stopping action. And again, about 20 times more stuff than I need.

Step 45:

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Ten very thin coats or so, applied as per label directions, and an overnight to dry. And it's looking nice.

Step 46:

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The weave pattern isn't the same as the original. Which is a bit of a drag. But otherwise, it's hard to tell there was ever anything wrong. From this angle, the slight bulge of the five new layers is visible. (the repair is on the left side of this photograph, directly opposite the blue tape.)

Step 47:

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Back outside to the brick wall where we started. Smooth and shiny. Now it's just a matter of screwing on some new parts and I should be back on the road. 

As an epilogue: I have ridden this bicycle almost 3000 miles since the frame repair. I haven't noticed any issues at all. I've left that little blue loop of tape on the left seatstay, directly opposite where the original hole was, so I can locate and carefully inspect the site of the repair. So far, it's holding up well.


Mr Brewster made it! (author)2017-05-16

Art, thanks for this write-up! I appreciate that you showed the good and the bad, stepping us through your thought process.
Below are a pile of pics from my repair. I included the CPVC pipe I used as my test, before going live.

The layup is a single piece of plain-weave, wrapped around about 10 times (I didn't count). Tape and pin-hole. Sanded, then topped with a single layer of 2x2 twill for looks/protection.

I even used your non-damage-side tape idea! For epoxying the fabric, I went with laying the fabric on plastic, soaking with resin, then a layer of plastic. A PVC pipe was used as a "rolling pin". this gave a nice sheet to work with. I also cut my sheet after rolling. This is good for reducing fraying.

The entire repair cost under $35. I have enough leftover material to do 10-20 more of these.

hommie17 (author)2017-01-19

Nicely done. I have repaired fiberglass boats which is similar to what you did. Three suggestions I would make is; (1) I was once told to initially fill the inside of the hole with aluminium foil so you have a backing for the epoxy. another way would be to inset a small piece of cf cloth that is saturated with epoxy into the hole and pull it up to the hole so it acts as a backing which also ensures you have the correct form of the stay being repaired. You can also use the good seat stay as a mold to make the backing from and once the piece has dried you can put epoxy on it and inset it into the hole (there is a wax you can use so backing piece will not stick to the good stay when making it). Hope this makes sense. Just pouring the epoxy into the hole means that the glop inside may break off at some point and rattle inside the tube. and (2) instead of making one sheet of cf cloth with 4 wraps I suggest using 4 individual wraps, each one slightly larger than the previous piece, by about and eighth of an inch along the edge. Place the smallest one first and then the next larger one, etc. This way you won't have to worry about excess epoxy or loose threads. There are rollers you can buy to make sure the epoxy soaked cf cloth lays flat and any excess epoxy will be squeezed out. and (3) use acetone to clean up. Also, as a footnote, for boats gelcoat is used which is harder than enamel paint and waterproof. It is harder to to use but you can mix and match different colors to get a match close to the original color.

Vincek100 (author)2016-10-23

thanks for all the effort you put into this, really helpful, I have a similar injury to my beloved Pinarello Prince ,must fix

ordyordy (author)2016-10-18

This is great! Any news on how the bike held up years after the repair?

TomC177 (author)2016-04-11

I have a few carbon fiber bikes, so I'm rich with bikes but with money...not so much. Anyway, one bike is a ten year old Specialized Tarmac Comp with a slightly damaged chainstay. Of course with carbon fiber, I keep reading that 'slightly damaged" is only a stone's throw from "catastrophically damanged", So I'm thinking, if I fix the Tarmac using your experience to guide me, then I can get out and ride it grinnin' - and sell one or more of the other bikes with little regret. Thinning the herd is a good plan anyway considering that I'm about 70 - but it is definitely fun to pick my ride according to which suits my mood, or is most appropriate for the day. You are so cool for doing this and writing this up so well and with an engaging style. Great work, man!

DanM45 (author)2015-08-27

What a great job!
im about to attempt this on a small crack in my frame along the lower chain stay, where did you get your carbon fabrick? or where do you suggest i get it from?

TripN (author)2015-08-11

Nice job with bike and documentation. A Loy better than the time I repaired a hole in my apartment's wall with mashed potatoes.

AshR (author)2015-06-14

This is exactly what I was looking for :) thanks so much for the instructable.

I'm off to mix up way too resin and get my repair on :)

rnorman3 (author)2013-02-28

the frame you have is a TREK frame, and if you take your frame into a TREK authorized dealer, they will warranty you a new frame. It may cost you a little, like if you need a new headset or BB. a new frame would be safer

art medlar (author)rnorman32013-03-03

I can't believe you are telling me this! This is _instructables_ not "purchase-ables". As I very clearly state in the opening paragraphs here, Trek does NOT "warranty" anything at all. They do have a "crash replacement" program which means that they will sell me a replacement frame for MORE THAN THE COST OF AN ENTIRE REPLACEMENT BICYCLE! It's basically a scam that they use in their advertising literature in an attempt to fool people who are not good at math. If you'll actually read what I spent the time to write in the introduction, you'll see that I already took that into consideration.

And I'm afraid I need to take issue with your unsupported claim that somehow a new frame would be "safer". Do you have any evidence that this repair is not "safe"? Do you have any metrics for quantifying this supposed "safety"? Because without them your claim just seems to be coming out of fear: the fear of experimenting, learning new processes, making something on your own. And retreats into passive consumerism.

brandon.boot (author)art medlar2014-12-17

I concur....same thing happened to me...very small minute ding in the seat stay area and TREK "crash replacement" option was BS!!! They offered me a brand new frame at market value -5%. I bought a kit off EBay and conducted my own repair. It's a 2013 Domane 4.0 CF. The repair came out awesome and thank you for your write-up!!! Ignore the "haters" I'm not worried about transferring any type of load because one seat stay is stronger than the other. This frame has ISO-flex in the seat post area, so that load gets transferred up stream.

SteveB4 (author)2014-10-08

Great job Art!

I stumbled across your instructable since I just bought a CF bike and wanted to do a little reconnaissance in preparation for some "likely" future issue. Your open-mindedness and willingness to tackle this project (even through necessity) is inspiring as well as very helpful to others who follow in your footsteps. I enjoyed going through it and appreciate the time and humor that you invested here. I will definitely refer to it when the need arises. Thank-you.

a-dog501 (author)2014-09-27

Hi, I have a similar problem on a carbon frame on the right hand side chain stay, due to its position in is next to the cable stop for the rear derailleur and possibly underneath it as it is epoxied in place. I am temped to try this method but speaking from experience would you wrap several layers around and either side of the stop or cut small holes in the fibre to allow the stop to poke through when going over the top of the stop. Thanks and well done on your well written instructable!

rick.stout.94 (author)2014-08-29

Good job Al. A little suprised about your comment about why Trek would put a "crispy, nominally repairable part right in the line of fire". Never seen a "carbon fiber" bike with steel, ti or aluminum chain stays. Of course they make mixed material frames with stays and other tubes of various materials but this is a carbon fiber bike.

PatrickF2 (author)2014-08-27

I cannot tell you how much of a Godsend finding this article was! I have discovered an area on my top tube that looks completely like only the clearcoat has sustained some type of crack. I examined the crack under high intensity light while wearing my surgical magnification loupes and it does not look like any of the CF is affected.

This coming Tuesday, I'm taking the bike to the surgery center where I do my surgeries, and I'm going to use the fluoroscope (portable x ray machine) as well as a diagnostic ultrasound machine to image this area of the crack to determine if any blowout of the internal side of the tube has taken place.

My question is this- If I find that there is no full-thickness crack, nor any blowout of the internal side of the top tube has occured, do I simply have to sand down the clear coat and re-spray it with the enamel as pictured in your instructable?

всмок (author)2014-08-13

I had my carbon fork cracked when I was hit by a car. In Ukraine got it peraired for $40 (at Garbaruk company). I am shocked by the $300 starting price in US, but I understand labor cost is much higher there.

alinezam (author)2014-07-24

Exactly the same thing happened to my Norco bike. However, while I was getting ready to follow these instructions, to my surprise, the company agreed to give me a new frame (I only paid for moving parts from the old frame to the new one). I just wanted to share some lessons I learned:

- keep the derailleur adjusted all the time

- keep track of the gear you are at (i.e., don't try to change gear in uphill if you are already at the lowest gear)

- regardless of how careful you are, carbon bikes don't last as long as aluminum or steel bikes

Finally, thanks to the author for this useful article and thanks to Norco for their great customer service!

Devinchi42 (author)2014-02-18

On my carbon frames, I topcoat with a final coat of the UV stable epoxy that I used for the carbon layup.

CobyUnger (author)2013-03-27

I did this to a bike months ago. Worked great and it's holding up really well..

toyowner (author)2013-03-16

Very nice repair.
Gelcoat is the ususal finish for carbon fiber and fiberglass as well.
Gelcoat is Fiberglass resin thinned with acetone so it can be sprayed. Not as easy as it sounds and is very hard on spray equipment.

toyowner (author)2013-03-16

use cellophane wrap and "squeegee" the resin out and seal it from air then you can wrap it in cellophane or tape to hold it. unless you could somehow vacuum it closed.

chuck190 (author)2013-03-04

I commend you for your courage, but there's a saying that "fools step in where angels fear to tread". A failed stay could lead to serious injury, even death in heavy traffic. I was biting my nails as I read each step.

I have done some modification work with carbon on my own bike, and I try to guarantee against failure by prayer. I also prepared myself by doing a lot of research. Here's some info that might help you and other readers:

1. I worry about your using 3 layers of carbon (of unspecified specs) mainly because the stays should be equal in strength and flexibility. If the repaired one is stronger, shock absorbancy from bumps will be unbalanced and could put the weaker side under loads that could eventually lead to failure. Frankly, if I were you, I would sand off the layers and get 24K carbon toe at This video demonstrates how to apply it I would apply it on BOTH stays. Give the damaged one an extra two layers.

Note that how the excess epoxy is constantly squeezed from the application. The problem with using the cloth like you did is that it's almost impossible to eliminate air bubbles in between layers, and this will cause delamination with time. If you want to use the excess cloth you have, cut it into ribbons about 1-1/2 to 1-3/4" wide and apply the way the demo shows how to do it with toe. But it could get quite messy and difficult to control because squeezing the epoxy will screw up the weave. The toe isn't that expensive. I think you can get the minimum for about $15.

2. The silicone balls don't strengthen a layup in your application. It's principle purpose is to keep the epoxy from running on vertical surfaces AND filling in spaces. I don't think you needed it, but it's not worth removing.

As I remember, you used West System epoxy - which is a good choice. You can also get advice from their technical staff. They are very very good and helpful.

I hope this helps. Like I say, I wouldn't assume the repaired stay won't give trouble - and injury with time because it violates some basic principles of carbon layups.

art medlar (author)chuck1902013-03-05

Thanks! I was not aware of 'carbon tow' and it looks like it might be useful for other types of repairs. To clear up some things that might not have been clear:

1. There are five layers of carbon fiber, not three. I'm not sure how to make that any more obvious in the instructions.
2. The silica (not silicone balls) was only used in the fill step, for exactly the purpose you suggest, and was not used for wetting the fiber prior to wrapping. I'll try to make that more clear.
3. The process of wrapping with plastic tape squeezed out a considerable amount of epoxy and air. From watching that video, I'm not convinced at all that the 'carbon tow' method is any less likely to have voids.
4. I think you're completely mis-calculating the danger from over-strengthening this section of tube. First, the tubes are extremely stiff to begin with, so even if there were any measurable extra stiffening of this section of the tube, it would likely be no more than a small percentage. And even if this section were over-stiffened, this section is only about 10% of the entire tube. So we're talking about *maybe* at most making the repaired tube 1% stiffer than the undamaged one. If this "unbalanced" condition is enough to cause a failure, I'd say the problem wasn't with the repair.

Finally, as I noted, I've put a considerable amount of mileage on the bike post-repair and I keep a careful watch on the repair site. No problems whatsoever.

I'm concerned that you claim this "violates some basic principles of carbon layups". Because you don't specify what those principles are. Aside from my mis-communicating that there actually were five layers and that the silica was not used while wetting the carbon fiber, did I do anything else wrong?

jheiss (author)2013-02-28

By "about 1/4 of the tube inside" do you mean you stuffed in enough to fill the tube a few inches in either direction (i.e. 1/4 of the length of the tube), or something more localized like 1/4 of the cross section of the tube right near the hole?

art medlar (author)jheiss2013-03-03

You're right. What I'd written made no sense at all. I wonder what I was thinking? Anyway, I've edited the text of this step to, I hope, be more clear about exactly what I did. Thanks for pointing this out!

actimm (author)2013-02-28

I haven't ever done a CF patch, but when I did fiberglass work what I found works best is actually to do the layers opposite what you did. start small and work to big. This way you only have one layer of "frayed" edging to smooth out rather than having a candycane effect of frayed material if you make a mistake with the epoxy.

art medlar (author)actimm2013-03-03

Oh wow. That never occurred to me! And it is, in retrospect, so obviously the right way to have done it. Thanks!

rob.rowlands (author)2013-03-03

Great job and so well explained. I like your style

voron88 (author)2013-03-02

Really nice job. I have done a lot of fiberglass work and you handled this like a

camp6ell (author)2013-03-01

This is the best instructable I've ever read. Exactly the right amount information - and disinformation - laced with human experience. Nice.
I'll be coming back here when I need to do this.

nmcrae1 (author)2013-02-28

I'm an aircraft mechanic and have experience with Carbon Fibre and repairs - and you did an admirable job. Your repair is probably stronger than the original frame is.
I was also impressed that you used tape to compress it and let the excess epoxy leak away - most people wouldn't think of that, but it is important for the strength of the repair. Too much epoxy weakens the matrix. Well done!

Yes, working with epoxy like this IS messy, and if you use liquid hardener (Methyl Ethyl Ketone Peroxide or MEKP) - be EXTREMELY careful with it - just getting the fumes of MEKP near your eyes can cause INSTANT blindness. Nasty stuff - be VERY careful with it, and wash your hands before you touch your eyes - even if you have gloves on! Cream hardener is less dangerous, but also much weaker, and not as easy to use in this kind of situation. Great work!

Slay. (author)nmcrae12013-03-01

Not to be sarcastic or anything, but you really are an aircraft mechanic, aren't you? Totally wish I had that job...

graydog111 (author)2013-02-28

Really nice job. I have done a lot of fiberglass work and you handled this like a pro. At least carbon fiber sanding dust should not make you itch like fiberglass does. Good instructable....very thorough.

wilgubeast (author)2013-02-28

Great documentation, and you certainly have a way with words.

maintann (author)2013-02-28

We'll done. An easy way to clean off sunset epoxy is with either alcohol or white vinegar. One of the tricks with sanding epoxy is judging how long to leave it to set. There is a period of an hour or so to a day or so depending on the epoxy and the temperature when it sands fairly easily, then it goes as hard as! Best if possible to do the sanding then.

lapsmith (author)2013-02-28

Excellent job and very well written. Thanks!

tqwinter (author)2013-02-28

By far the best Instructable I've ever seen! Thanks for taking all the time to document each step carefully and with outstanding photos.

JamesRPatrick (author)2013-02-28

Wow that repair looks professional!

oneline180 (author)2013-02-28

You seem to have done things with care, therefore you should not worry too much about the repair you made.

Well done. Now go ride your bike more often.

alames (author)2013-02-28

Don't know if it would have helped, but methyl alcohol is a thinner for epoxy. With a very small amount you can make the epoxy more like a thin paint, and you can also clean up your brushes if you get to them before it cures. You can buy at the hardware store, or some hobby shops (model airplane and car types with gas engines) might sell you some if you bring your own bottle.

razorblade73 (author)2013-02-28

Best instructable ever, well done keep up the good work, very brave of you

DreamHazard (author)2013-02-28

Excellent job! Especially considering having had no guidance you've done a brilliant piece of work :)

Workstead (author)2013-02-28

This is a great instructable. It is written by someone who has been there. In my wotking life I was a technical writer and this is one well written article. If I ever need this type of repair I now have the knowledge to do it properly, without making mistakes that I otherwise would like have, because of your cautions about the wrong way to do it.Thanks,

DreamHazard (author)2013-02-28

A commonly used technique here is to pre-pierce the tape beforehand so the excess resin can bleed through the tape, resulting in a tighter wrap and (theoretically) less mess to sand off afterwards.

WVvan (author)2013-02-28

A most excellent instructable. Double plus good!

mikeyc.2009 (author)2013-02-28

Good job! Like maintann said alcohol does a great job cleaning off uncured epoxy. I get the 99% stuff from a local beauty supply shop. A good place to get small amounts of carbon fiber fabrics and tapes is hobby shops that specializes in radio control airplanes. They will also have a epoxy resins there too.

phburns (author)2013-02-28

Very nice explanation, thank you.

Nico3ck (author)2013-02-28

Carbon fiber itself is very strong, you don't really need to put a blob of epoxy inside your tube (but it can help while wrapping).

On simple way to use epoxy & carbon (or glass) fiber is to cut the fiber in a long strip, "paint" it with epoxy (fiberglass will be clear when enough epoxy is inside, carbon is a bit more tricky) and then wrap it tight around the sanded part.
You dont need to wrap it with plastic after, but you can add a special cloth with will absob the excess resin and limit the finishing sanding.

To work with epoxy, temperature is important (> 15 C°), the air must also not be moist. You will need to paint or varnish it, uv rays will tarnish your resin.

Sanctus (author)2013-02-28

One of the best instructables. Normally, I don't read attentively what really doesn't concern me, but this was awesome! I couldn't stop! Thanks!

Muddypaws (author)2013-02-26

Great Instructable. I am thinking about doing some carbon fibre soon (not a bike frame though), and your guide has given me a lot of tips about the pitfalls of carbon fibre with no experience and less than ideal workshop conditions. Thank you!

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