# Carbon frame and chipped clear coat question



## DirtSS (Mar 23, 2004)

I'm looking at buying a carbon fiber frame and it has a number of chips in the clearcoat and need to know how to tell if there is structural damage to the frame. I can't see any real damage so I was wondering if it might be safe or not.

If there is a better forum for this then I will ask it there.

Thanks in advance.


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## bhsavery (Aug 19, 2004)

as long as no fibers are broken


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## strike30 (Oct 4, 2005)

*Coin Tap Test*

Lacking a portable ultrasonic scanner, the next best method of detecting subsurface interply delamination is to simply tap the damaged are with a coin. First you "tap" a known intact area to get a "feel" for the "good" auditory response, and then go over the suspected damaged area listening for dinstinct tone changes. If the tone doesn't change you generally have no internal delamination - no significant structural damage. A Google search for "coin tap test" will yield further info. 
Internal delaminations in composites tend to be larger than the surface deformations ...a larger area may be damaged underneath than is apparent from the visual inspection of the outer surface, kind of like an iceberg. - (IMHO from an ex-composites NDE Engineer.)


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## jakeplazma (Oct 15, 2004)

What should be used to protect the 'delaminated' or chipped clear coat area?


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## kustomz (Jan 6, 2004)

jakeplazma said:


> What should be used to protect the 'delaminated' or chipped clear coat area?


Any readily available quick-set, two part clear epoxy will work. You will usually find Loctite brand in the hardware store with the double sided tube and that should work fine.


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## jakeplazma (Oct 15, 2004)

kustomz said:


> Any readily available quick-set, two part clear epoxy will work. You will usually find Loctite brand in the hardware store with the double sided tube and that should work fine.


Thanks Kustomz... What about fingernail enamel/polish? Would this work?


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## kustomz (Jan 6, 2004)

The clear nail coat may take several applications to build up any thickness, but if you have the time.........

For the seatpost I would just use Pledge furniture polish. It will hide most of the scratches until it is washed or wears off.


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## mudrider (Jul 4, 2005)

*BECAREFUL ABOUT APPLYING EPOXY TO FRAME!!!*
I don't have a lot of chemical experiance but from what I know the epoxy, fingernail polish, or standard clear coat could react with the resin (glue) in the carbon weave and make it weaker.
I would call the frame company and explain what you are doing. They probably won't tell you or give you any replacement resin (propriotary reasons) but they will be able to tell you what chemicals are ok and which to stay away from.


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## strike30 (Oct 4, 2005)

*Likely "non-reactive"*

Since the prepreg resin originally used in the frame is probably a cross-linked thermoset epoxy (EA934 or similar), applying a consumer room-temperature cure epoxy, urethane or polyester resin to the surface shouldn't harm it. 
Recall that the original reason for this post was to ascertain the frame integrity, then it shifted to repair of cosmetic (surface clearcoat) defects. If you are first satisfied that the frame is free of structural defects - no broken fibers or hidden delaminated plies, then you can resolve the cosmetic issues as suggested. If you have structural defects, you should stay away from the frame as it is nearly impossible to repair to original structural capability without the proper tooling, field kits and procedures. (IMHO from a former Advanced Composites Manufacturing Research Engineer.) - BV


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## Sorbut (Mar 7, 2006)

a few late quick comments: dont use epoxy to clear coat - its not UV stable with few exceptions. use polyester or vinyester. Epoxy is curing (not catalysed) and once cured is not very reactive. Secondary bonding on prepreg is problematic so rough fixes are not good. C/f epoxy structures have miniscule elastic deformation meaning they fail catastrophically - so if it aint broke its usually OK. This also means you can test it to very near destruction with no damage from the testing. Internal delamination is usually manufacture related. Microcracking can occur from damage and propogate through the laminate - you can not see nor pick up with a coin. THe coin trick will pick up air voids in a crap laminate. I have a c/f manufacturing business and looked at several bikes. In general I would say they are not great laminates with high resin to fiber ratios and I do know what I am looking at and I cant really tell if impact damage has done real damage. Having said that C/f epoxy is pretty strong, made with varying fiber orientation and will take a lot of hits before stuffed. Watch the joints and dont drill holes in it. If you do never has sharp edges as they focus loads and result in cracking failures.


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## kustomz (Jan 6, 2004)

Sorbut said:


> I have a c/f manufacturing business and looked at several bikes. In general I would say they are not great laminates with high resin to fiber ratios and I do know what I am looking at and I cant really tell if impact damage has done real damage.


Where have you been all our lives? We amateurs need this kind of help.......... Have you ever thought of posting a DIY carbon maintenance and perhaps even a build up website? I have a set of tubes from Mclean just setting in my basement waiting for the right homebrew process to help me assemble them.


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## Boogie Man (Sep 27, 2005)

Sorbut said:


> a few late quick comments: dont use epoxy to clear coat - its not UV stable with few exceptions. use polyester or vinyester. Epoxy is curing (not catalysed) and once cured is not very reactive. Secondary bonding on prepreg is problematic so rough fixes are not good. C/f epoxy structures have miniscule elastic deformation meaning they fail catastrophically - so if it aint broke its usually OK. This also means you can test it to very near destruction with no damage from the testing. Internal delamination is usually manufacture related. Microcracking can occur from damage and propogate through the laminate - you can not see nor pick up with a coin. THe coin trick will pick up air voids in a crap laminate. I have a c/f manufacturing business and looked at several bikes. In general I would say they are not great laminates with high resin to fiber ratios and I do know what I am looking at and I cant really tell if impact damage has done real damage. Having said that C/f epoxy is pretty strong, made with varying fiber orientation and will take a lot of hits before stuffed. Watch the joints and dont drill holes in it. If you do never has sharp edges as they focus loads and result in cracking failures.


ok, so if I have a chip in the clear coat on my carbon bars, and it looks like it may run all the way to the fiber, and I wanted to patch up the clear coat to prevent any damage to the fibers, I should use a polyester or vinyester clear coat? Where would I obtain something like that, at a hardware store? Also, would it be help to prep the area by sanding with a very fine grit sandpaper? thanks.


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## Sorbut (Mar 7, 2006)

clearcoats are not a repair. they are just to make it pretty and keep UV off the epoxy as it goes yellow. Any boat supply shop has vinyl of polyester. Use gloves and dont sniff it by the way. Damage to the fiber should be obvious. If you need to repair then definitely sand it. Any bond to a fully cured epoxy is NOT chemical. It is mechanical so it relies on the surface being rough to key in. In reality you cant repair damage with resin. You can cover the fiber. when sanding if its black dust its to the carbon. Use a magnifying glass and just look at it. Stress the thing as hard as you expect to use it and see if it breaks, Sounds rought but as above it wont damage it. If you hear cracking thats fibers breaking. that woudl generally only occur if it has extra damage you dont see or it has a lack of resin inside. The guys that make this stuff will overbuild I expect (given the suing that you guys love to do). Without seeing it, I would expect a chip in the clearcoat would do no structural damage.


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## Boogie Man (Sep 27, 2005)

Sorbut said:


> clearcoats are not a repair. they are just to make it pretty and keep UV off the epoxy as it goes yellow. Any boat supply shop has vinyl of polyester. Use gloves and dont sniff it by the way. Damage to the fiber should be obvious. If you need to repair then definitely sand it. Any bond to a fully cured epoxy is NOT chemical. It is mechanical so it relies on the surface being rough to key in. In reality you cant repair damage with resin. You can cover the fiber. when sanding if its black dust its to the carbon. Use a magnifying glass and just look at it. Stress the thing as hard as you expect to use it and see if it breaks, Sounds rought but as above it wont damage it. If you hear cracking thats fibers breaking. that woudl generally only occur if it has extra damage you dont see or it has a lack of resin inside. The guys that make this stuff will overbuild I expect (given the suing that you guys love to do). Without seeing it, I would expect a chip in the clearcoat would do no structural damage.


Thanks for the info. The chip is somewhat deep which has me worried. It's on a brand new pair of Race Face Next SL Riser Bars. They seem really solid, so it probably wont' be a problem. I also e-mailed Race Face to see if they had any recommendations and I'll post their response whenever I get it.


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## Sorbut (Mar 7, 2006)

Be real interested to see what they say. If you have to repair it then if there is a boat builder about see if you can buy a small amount of 200 gram twill prepreg. Its got resin in it. Sand area then wrap three or four layers around the area then wrap it with stretchy insulation tape. Put it on BACKWARDS so the stick is on outside with a BIT of stretch to compact the laminate. THe tapes do not bond with epoxy. Use cellulose (cellotape) as a release for stuff you dont want it to stick to. Then put it in the oven at say 90 degrees for 1.5 hours. Ask makers if this temp is OK as their resin may be lower cure. If so, or they wont tell you, go for 60 degrees for 4-5 hours. 60 is a minimum usually to get prepreg to cure. There are some low temp prepregs available but not used much. IF anyone has some use it. OR use dry carbon with resin and tape as well. Just not so tight as it may squeeze all the resin out. Cook at lower temp, or if using room cure then just heat it a bit to help it along. If yu need to do this you can ask me some more.


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