Carbon Fiber repair

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#1

I repaired a bike frame made of carbon fiber (Specialized fact r11 type) It has 2 cracks the one next to the other. The method i decided to use is wrap Cf around the crack 0 +45 and - 45 degrees -330gr/m2 unidirectional prepreg. Everything seems to go smoothly but i have one question . The procedure i used was this :
I sanded the primer paint coat and exposed the existing carbon fiber in the whole area i was ging to wrap new cf
Then i used some repair paste to close the crack , then i sanded again the repair and last I wrapped Cf around the area i sanded …then vacuum and inside the oven.
I DID NOT USE PRIMER or any bonding agent to bond the old with the carbon fiber.

  1. Should i worry for delamination ?

  2. I want to repaint the whole frame. Can i use the type of paints used for motorbikes or i have to use special primers / paints for carbon fiber?

#2

Automotive paints will be fine.

What grit sandpaper did you use? You don’t need a primer to bond to carbon, so long as the surface is clean and mechanically keyed you will get a very strong bond.

#3

I started with 120 and went up to 800 …the surface i layed the new cf was very smooth…but i couldnt have used a different grit because the thicknes of the part at the repair spot was 0.5 mm !..so i couldnt grind the old cf to get mechanical bond…if i left it to 120 then the new cf would be some touching cf and some other touching paint or primer

#4

You only wrapped it with one layer of 0 +45 and - 45 degrees -330gr/m2 ? That’s not enough to get a good strenght.

#5

I wraped 3 lawyers of 330 gr / m2 Unidirectional carbon fiber with laminate thickness around 1.5 mm
The existing laminate that got fixed had the same layup scedule but instead if 3 layers of 330 gr the used ( i suppose) 3 layers of 100 gr / m2 of unidirectional. I examined the thickness if the existing tube and it was 0,5 mm
. I didnt have thinner prepreg so i used the 330 i i had i would go for 200.

#6

Ok, then ther is nothing to get worried about.

#7

I did nearly the exact same thing with an old Kestrel frame with a cracked top tube. The previous owner had filled the crack with a general 2-part epoxy after the crash and then put it on the shelf for a few years before deciding to sell it. I sanded down to the carbon before wrapping with a mix of some Textreme sample swaths and scrap 3k twill. Wet out with Pro-Set and vacuum bagged for consolidation. Sanded smooth, painted and polished. Been going strong for almost 2 years now with no issues.