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Blotchy used carbon fiber frame

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Blotchy used carbon fiber frame

Old 02-02-20, 08:48 AM
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oik01
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Blotchy used carbon fiber frame

I got a black vintage trek 5000 from 2005. Theres a few surface scratches on the bike but then there's also random blotches that are most prominent underneath the seat post but present elsewhere. The first I blotches are super smooth to the feel and in most places if I closed my eyes I wouldn't know where they are. Cotton doesn't stick to them either. At first I thought they maybe we're attempts to cover up paint issues but I'm not so sure anymore. I read in other posts that carbon fiber can give this type of blotchy look if there's a clear coat covering it only. I'm not sure if this is how that would look. My bike is black w painted decals and I'm not sure if that means the material is black or the frame was painted with a black coat. Anyways the pictures are below for the more knowledgeable than me:



With flash they really come out lol:



Owner said the bike was examined at a bike shop and no cracks ... It passed the tap test, it's smooth to the feel in that area and a cotton doesn't get stuck there but hey what do I know ... Our deal was I can return within a few days if major issues become obvious with the bike that weren't known before ... If it's just cosmetic I'm inclined to keep it
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Old 02-02-20, 08:58 AM
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That's the way carbon is supposed to look.
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Old 02-02-20, 10:13 AM
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I would be more concerned about the large area at the top of the seat tube which looks like the clearcoat may be delaminating. The seller SAYS that they had it checked out, you might want to verify this with your own expert.
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Old 02-02-20, 11:22 AM
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I have seen a couple of frames with clearcoat problems. I think it is repairable, but would take some work.

I can't tell from the photos above. There are some carbon weaves that will have a patchy appearance, but it would be obvious when looking at the bike in person.
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Old 02-02-20, 12:59 PM
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On many carbon consumer products the top layer is a cosmetic one. Chosen for the "look". To my eyes it looks like a bit of the clear coat has come off, as dsb said. Andy
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Old 02-02-20, 03:26 PM
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Originally Posted by Andrew R Stewart View Post
On many carbon consumer products the top layer is a cosmetic one. Chosen for the "look". To my eyes it looks like a bit of the clear coat has come off, as dsb said. Andy
Im guessing this shouldn't be an immediate safety issue. Would it make it more likely to fracture the exposed carbon from contact with other surfaces from a fall or other bikes on my rack ECT?
Would the paint job be doable by myself? I'm ok following videos and reading but my concern is I can imagine it can be messy for the area you do it in and I don't have a garage to work in.
Alternatively how much would bike shops charge to do something like this? Would car places be adequate? Anyone know experienced fair shops in the jersey city area that they would recommend??
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Old 02-02-20, 03:46 PM
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There are no obvious defects shown in the OP's photos.
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Old 02-02-20, 04:50 PM
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Originally Posted by oik01 View Post
Im guessing this shouldn't be an immediate safety issue. Would it make it more likely to fracture the exposed carbon from contact with other surfaces from a fall or other bikes on my rack ECT?
Would the paint job be doable by myself? I'm ok following videos and reading but my concern is I can imagine it can be messy for the area you do it in and I don't have a garage to work in.
Alternatively how much would bike shops charge to do something like this? Would car places be adequate? Anyone know experienced fair shops in the jersey city area that they would recommend??
Carbon frames don't like pinpoint impacts. So, yes, a fall down or contact with a car rack could be the start of a failure. Generally surface stuff isn't as much as a concern (excepting when changes are focused on the bonded edges like a frame joint [if applicable] or a braze on bit).

Refinishing the frame is certainly an option but we see so many cobbed up home spray jobs that suck and take value away from a bike that it's hard to think someone asking for advice about doing this would do a nice job... Andy
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Old 02-02-20, 05:13 PM
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My black BMC carbon frame has not identical but similar-looking stuff all over it. I freaked when I first noted it and took it to the shop. Spent a lot of money on that bike. They laughed and said this is how all black CF frames look. Bike works fine.
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Old 02-02-20, 05:46 PM
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Carbon fibre is an interesting material. As a golfing professional I began using it in the late 80's. And it is funny that trends seem to start in the auto industry (Indy car) and then into golf and then into cycling. Cf is the same way. I first ran into it at Indy, then Golf, then Cycling. So I have a bit of experience with CF. Most tube materials are made in two methods. Both involve wrapping carbon fiber either sheets or filaments around a steel mandrel,and them place in an oven at 250* F for about six hours. The sheets and individual filaments are coated with a matrix which is what the CF is held together by. The matrix seals together under the heat in the oven and the tube comes out as a complete unit. The tubes are then sanded to a uniform shape (round) and coated with a protective layer of paint. some times clear coat, but paint non-the-less.
Carbon fibre is damaged by hits or dings to it, or by heat. The nicks and dings create spider cracks in the CF which eventually lead to complete failure. The major reason you don't see the same cars at Indy year after year, is just that; they have so many dings from road debris that an X-ray of the tubs will show thousands of those tiny spider cracks. Heat on the other hand breaks down the matrix holding individual carbon fibres together. The amount of heat need to break down CF is about 350* for one minute. Lower temperatures for prolonged periods can also do the same damage.
That brings me to say that the things you are seeing are damage to the clear coating on your frame. Likely from UV exposure. You can have the clear coat repaired,by an over-spray to the whole bike. However the warnings from auto paint specialists apply: if you have an enamel clear coat and you shoot over it with lacquer, the whole thing can bubble up destroying both finishes. So test before re-spraying.
The heat as mentioned above destroys CF matrix, so what ever you do "DO NOT POWDERCOAT" the PC finish is heated in an oven long enough to breakdown the CF under the coating.
Here area few pics of Carbon fibre tubes at the juncture of the raw tube and the clear coating paint, and one with regular paint and then clear over spray. HTH, MH

Notice the switch from dull to shiny, this is sheet wrapped CF

This is filament wound CF in the blue shaft, it has paint then clear coat. Both shafts for side by side comparison
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Old 02-02-20, 11:36 PM
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Originally Posted by Mad Honk View Post
Carbon fibre is an interesting material. As a golfing professional I began using it in the late 80's. And it is funny that trends seem to start in the auto industry (Indy car) and then into golf and then into cycling. Cf is the same way. I first ran into it at Indy, then Golf, then Cycling. So I have a bit of experience with CF. Most tube materials are made in two methods. Both involve wrapping carbon fiber either sheets or filaments around a steel mandrel,and them place in an oven at 250* F for about six hours. The sheets and individual filaments are coated with a matrix which is what the CF is held together by. The matrix seals together under the heat in the oven and the tube comes out as a complete unit. The tubes are then sanded to a uniform shape (round) and coated with a protective layer of paint. some times clear coat, but paint non-the-less.

Carbon fibre is damaged by hits or dings to it, or by heat. The nicks and dings create spider cracks in the CF which eventually lead to complete failure. The major reason you don't see the same cars at Indy year after year, is just that; they have so many dings from road debris that an X-ray of the tubs will show thousands of those tiny spider cracks. Heat on the other hand breaks down the matrix holding individual carbon fibres together. The amount of heat need to break down CF is about 350* for one minute. Lower temperatures for prolonged periods can also do the same damage.

That brings me to say that the things you are seeing are damage to the clear coating on your frame. Likely from UV exposure. You can have the clear coat repaired,by an over-spray to the whole bike. However the warnings from auto paint specialists apply: if you have an enamel clear coat and you shoot over it with lacquer, the whole thing can bubble up destroying both finishes. So test before re-spraying.

The heat as mentioned above destroys CF matrix, so what ever you do "DO NOT POWDERCOAT" the PC finish is heated in an oven long enough to breakdown the CF under the coating.

Here area few pics of Carbon fibre tubes at the juncture of the raw tube and the clear coating paint, and one with regular paint and then clear over spray. HTH, MH



Notice the switch from dull to shiny, this is sheet wrapped CF



This is filament wound CF in the blue shaft, it has paint then clear coat. Both shafts for side by side comparison


So my frame is CF with a black paint coating and then clear coat or is that bare CF with a clear coat? If its just bear CF with a clear coat does that mean potentially less sanding time if I decide to risk it and do the job? How would I make sure I don't sand out a layer of the CF as I sand through the clear coating?


I don't like the look of the blotches but im not sure by how much lol. But looking into this thing lead me to reading about many frame repaints and I am honestly itching to do it. The reason is that I like the bike but I know that if I do my own paint job I will absolutely fall in love with it. I would need to read a lot more and watch more videos. My bike has an orange handle bar tape and im waiting for an orange seat. Lots of people have complimented me on that touch and I can really imagine a matte black finish with random artsy spots of orange and blue, while keeping the orange handle bar and seat. I think it would be very unique.


I would obviously need to read a lot more. I can tell a lot of people are suggesting here that I just stop my mind from going down that route and accept the frame as is?


If I were to do this, the process would involve?!!

a) stripping down all components including bearings to just have the frame standing by itself

b) Wet sanding the frame ( likely the longest part?). Its mostly just black similar to the part I showed you except for a trek sign and a decal on the top-tube. Im guessing there aren't many paint layers for me to go through? My worry is figuring out when to stop sanding and would have to read more and look at videos/ pictures.

c) Apply paint primer layer

d) Matte black paint x several layers letting it dry in between.

e) Apply random orange/ blue paint spots

f) several clear coats for protection.

g) reassemble bike?


This is the look I would be wanting to replicate along with the orange accessories.


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Old 02-03-20, 07:09 PM
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If you are going to repaint it with the flat black paint, there is very little need to remove the paint layer already on the frame. You will only need to give the clear coat that is currently on the frame, a light sanding of 600 grit water sand paper. That will scuff up the current paint enough for the flat black paint to adhere to the frame. Your choice of final finish is then up to you. Like I said, it it is not damage to the CF but more just uv damage to the current clear coat. Have a good time painting it. Smiles, MH
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