# Repair a carbon frame using fiberglass??? Anyone??



## juancho142 (Feb 26, 2010)

Hi guys, I don't know if this fits here, if not let me know. Here's my problem:
I have a GT Force Carbon that has cracked in the front triangle and I'd like to try and fix it myself, either permanently or at least until I can find a replacement front triangle, which won't be easy.
Unfortunately, in my country I've been searching the web and CF is not something easy to find. Fiberglass is though. 

I've googled fixing CF with FG but I haven't found anything answering this particular question. IS it possible to fix CF with Fiberglass patches? Or should I just get a CF and resin kit from Ebay? If so, is there any thickness or a particular type of fiber I should use?

Thanks in advance.

Juan


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## juancho142 (Feb 26, 2010)

Seriously? No one?


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## Calvin27 (Mar 25, 2014)

Yeah, no don't do it. 

Carbon fibre is not the same as fibreglass. Obviously the fibres are different but so is the resin. I don't know where you are but just order some prepreg cf sheets and maybe a little resin. i don't see how you could get fibreglass but not cf..?

As for the patch job, a patch job is pretty bad engineering. The strength of carbon fibre is in it's long continuous strands that lend strength and stiffness. A patch pretty much means you have only resin holding the broken part together. You may as well just superglue and you will have pretty much the same strength. 

I'm not sure if you plan to keep the frame or get it professionally repaired, but you will need to think this through carefully. If the crack is in the centre of the tube this is a good thing and all you need to do is reinforce that area with lots of overlap with the original material. Ideally you want to sand back the clear coat and re-bond the material adding material thickness equal or greater than the original tube. 

If the crack is somewhere complicated (i.e. bottom bracket) you are in a world of pain. Your frame is pretty much done for and the best patch you can do it to chuck as many layers as you can in the region and reinforce around it too. You don't want stresses being transferred somewhere else. 

Personally, I would not even bother to 'fix' a carbon frame even for a professional. This material was not made to be repaired.


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## Cayenne_Pepa (Dec 18, 2007)

I would pay Calfee to fix it. So what if they charge $600? They even paint it back to original finish, for that price! The BEST carbon repair in the cycling business....and, if you really LOVE that GT - you'd pony-up the cash.


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## ktm520 (Apr 21, 2004)

Technically yes, you could use fiberglass to repair the defect, if you know how to design the repair. The tensile strength of glass fibers is lower than carbon fibers, to varying degrees. The type of resin you use is also really important. For a newb, I'd stay away from prepreg's. The ebay kit may be your best bet. Go for it, but I'd be prepared to scrap the frame if you screw it up or chance a trip to the dentist. There is also that whole separate conversation about safety . . .


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## ktm520 (Apr 21, 2004)

Calvin27 said:


> As for the patch job, a patch job is pretty bad engineering. The strength of carbon fibre is in it's long continuous strands that lend strength and stiffness. A patch pretty much means you have only resin holding the broken part together. You may as well just superglue and you will have pretty much the same strength.


Not true. A correctly designed repair is as strong as the parent structure. The real challenge with composites is how process critical/intensive they are. Follow the recipe to the T and you are golden. Make one little mistake along the line of many steps and you have a failure.


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## bigflamingtaco (Oct 26, 2013)

If you've never worked with CF before, this is not the time to learn. Laying up CF is less tolerant of the learning curve, and you don't want to learn by having a tube rammed through your gut, ass, or worse.


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## bradoemba (Jun 18, 2004)

You can mix fiberglass and carbon fiber without issue. The resin is the key thing. Make sure you know if it is epoxy or polyester. Most likely epoxy.

As mentioned, you will need to get trough all the paint down to the CF. have plenty of overlap around the crack and wrap all the way around the tube, thereby creating a sleeve. This will certainly be a quick-and-dirty fix. You will be adding layers that you can't smooth down to look like it was when new.

Depending on where the crack is, this may not be possible or smart given how the loads and stresses are affecting that point on the frame.

And uh....how did it break in the first place? Tells me this was a high-stress area that was strong enough to begin with.

Good luck?


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## compositepro (Jun 21, 2007)

Scuff it up and stick a fibreglass patch on it ,providing its actually e or s glass cloth and not some kind of chopped spray matt E glass actually has a tensile strength equal or to some types of carbon S glad is in some cases much higher

The thing Carbon has that glass fibre doesn't is Modulus or stiffness which isn't so important if you overmatching the strength of the underlying repair

There's plenty of literature out there on topics such as GLARE and composite panel repair ,we actually teach people to do this in the UK and to be honest the two are the same but slightly different


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## Bikerector (Jan 24, 2014)

I'm pretty sure you can get carbon fiber "fabric" from marine supply stores, probably where you'll end up getting the fiberglass repair stuff.


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## jgrano (Dec 5, 2011)

I'd just order a CF kit from ebay, it will be better than fiberglass. The process is pretty easy. Just sand down around the area & clean it off. Put some mixed epoxy on the surface and put some pre-cut patches of CF on while alternating epoxy layers. You can do a ghetto job of wrapping the tape with electrical tape (sticky side out) to get some compression on it. Let it cure and sand it down. 

Not the best method but it will probably out last the rest of the frame unless you do a really poor job.


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## Calvin27 (Mar 25, 2014)

ktm520 said:


> Not true. A correctly designed repair is as strong as the parent structure. The real challenge with composites is how process critical/intensive they are. Follow the recipe to the T and you are golden. Make one little mistake along the line of many steps and you have a failure.


Really? A virgin monocoque frame is going to be a strong as a patch job? I've never heard such a thing. The only way it can possibly be stronger is if you reinforce it so that the new material has more strength than the older one. Which is pretty much remaking the tube section.

Without knowing the failure method (fibre crack, delamination, etc) there are not many failure means that would make the patch stronger than before. If that was the case used carbon frames would sell at a premium.

Like I said, professional repair job or just over design it (i.e. lots of layers and overlap with frame).


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## jgrano (Dec 5, 2011)

Just look at this - http://calfeedesign.com/repair/repair-technique/ and follow the steps.

But wear a dust mask at least and clean the area before you put epoxy on it. Calfee really over does the repair patch area.

take a look at this too - http://forums.mtbr.com/tooltime/diy-carbon-fiber-frame-repair-920370.html


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## ktm520 (Apr 21, 2004)

compositepro said:


> Scuff it up and stick a fibreglass patch on it ,providing its actually e or s glass cloth and not some kind of chopped spray matt E glass actually has a tensile strength equal or to some types of carbon S glad is in some cases much higher
> 
> The thing Carbon has that glass fibre doesn't is Modulus or stiffness which isn't so important if you overmatching the strength of the underlying repair
> 
> There's plenty of literature out there on topics such as GLARE and composite panel repair ,we actually teach people to do this in the UK and to be honest the two are the same but slightly different


Matching stiffness is almost more important than strength as to not cause stress concentrations at the edges of the repair. I'm not real familiar with how folks repair bikes. Like any structure . . . it depends.

Let's see some pics of the defect.


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## JohnnyMagic (Dec 7, 2014)

Have repaired 100's (or almost 100) carbon frames.
Can't really recommend a repair (without an evaluation)

Carbon frames are easily repaired to as-good-as or stronger than the original.

Calfee charges WHAAT???!!!



What country???


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## juancho142 (Feb 26, 2010)

JohnnyMagic said:


> Have repaired 100's (or almost 100) carbon frames.
> Can't really recommend a repair (without an evaluation)
> 
> Carbon frames are easily repaired to as-good-as or stronger than the original.
> ...


I'm from Uruguay and I've searched the classifieds for carbon fibre + resin but haven't found any CF yet, hence the fiberglass question.


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## NYrr496 (Sep 10, 2008)

Dude. Carbon fiber cloth is all over Ebay.


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## TrailMaker (Sep 16, 2007)

Now you know why none of the frame guys weighed in.


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## Guest (Jan 23, 2015)

Carbon Repair Another repair option.


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## the-one1 (Aug 2, 2008)

Forster said:


> Carbon Repair Another repair option.


Kind of far from Uruguay


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## juancho142 (Feb 26, 2010)

NYrr496 said:


> Dude. Carbon fiber cloth is all over Ebay.


Yeah I know, but it's more expensive and takes like 2-3 weeks to get here, fibreglass is easy to find so I thought I'd ask before.

BTW, are these kits good for fixing this?

Carbon Fiber Fabric Kit Plain Weave Cloth 72" x 14" | eBay

Carbon Fiber Cloth Nano Particle Epoxy Resin | eBay

If not what kind of fabric should I look for?


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## NYrr496 (Sep 10, 2008)

juancho142 said:


> Yeah I know, but it's more expensive and takes like 2-3 weeks to get here, fibreglass is easy to find so I thought I'd ask before.
> 
> BTW, are these kits good for fixing this?
> 
> ...


I couldn't tell you.


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## Drew Diller (Jan 4, 2010)

Been gone a few days.

Check out Drew Wilson aka Cyclocarbon


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## Cayenne_Pepa (Dec 18, 2007)

That ebay carbon fiber is for cosmetic-only wraps(automotive, etc.). Most bikes are made of Toray Industries(Japan) T700 pre-impregnated(prepeg) carbon sheets.


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## compositepro (Jun 21, 2007)

ktm520 said:


> Matching stiffness is almost more important than strength as to not cause stress concentrations at the edges of the repair. I'm not real familiar with how folks repair bikes. Like any structure . . . it depends.
> 
> Let's see some pics of the defect.


yep your over thinking it


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## juancho142 (Feb 26, 2010)

I just found this kit which has a very reasonable price, will it do?

This is the kit: Real Carbon Fiber Epoxy Resin Kit 2x2 Twill 36" x 6" | eBay

This is the part that's broken (I'll add better pics later):










The carbon around that bolt wore out and developed some play, which eventually made ir snap. I`d sand the area around it and add a couple of layers of carbon to strenghten the area.


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## Calvin27 (Mar 25, 2014)

That is a tough fix. Id be leaning towards using a hard filler but even then not sure it will hold.

It's a high stress area and the bolt increased the stress concentration. I'd be looking for a new frame tbh.


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## juancho142 (Feb 26, 2010)

I'm looking already, but in case it doesn't show up i'm looking to fix it.


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## NYrr496 (Sep 10, 2008)

Zachariah said:


> That ebay carbon fiber is for cosmetic-only wraps(automotive, etc.). Most bikes are made of Toray Industries(Japan) T700 pre-impregnated(prepeg) carbon sheets.


See that? I did not know this... Exactly why I didn't claim to know.


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## bradoemba (Jun 18, 2004)

I don't think you can fix that with composites alone. Only way I could see making that safe would be to machine some kind of metal sleeve around the hole and then bonding that in like a splint.

Sorry (I mean congratulations!) but it's time for a new bike.


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## Drew Diller (Jan 4, 2010)

OP if you're really going ahead with this, are you planning on taking the frame apart first? Can't see much at all from that image, but this does look like a tough fix for a first attempt.

If it was a relatively flat spot it'd be a different story. Play it safe.


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