Carbon Fiber scratch repair

[wleehendrick]

OK, a little off-topic, since this pertains to my wife's 135i, but potentially applicable to FFR's aero parts. I trust the experienced opinions of forums members here more that random google searching, so hopefully someone can weigh in...

My wife got rear-ended this week, luckily it was a minor impact with just cosmetic damage to to rear bumper cover and carbon fiber diffuser. This is an OEM BMW part I installed which replaces the lower rear valance. I'm sure it's pretty ineffective aerodynamically, but looks much better than the stock gray plastic (see image of part below).

She took it to Amato's (a great body shop in SD) and got an estimate of $2700 to replace the diffuser and paint blend the damage on the bumper cover. Even they suggested taking the check form insurance not bothering to repair. I'm not going to do anything to the paint except polish, since at some point the bumper is sure to get more damage. However, I'd like to repair the scratches in the c.f. some are deep enough to require filling for a proper repair (the part is not cracked, and it's not structural, so they're no concern there).

What epoxy/resin and rubbing/polishing compound would you all recommend to fill in a deep scratch (couple mm's) and then smooth it out? Appearance is the only issue.

Thanks!


https://www.sonicms.net/image/cache/data/bmwperf/e8x/rear-750x750.jpg

[CHOTIS BILL]

I have never made carbon fiber parts where the CF showed but I have been told bay a friend that has there is a special resin that is used instead of actual gel coat You might get some help form companies that specialize in composites such as TAP plastics. I would think you could fill the scratches with the special resin and then sand and buff it out like you would do with gel coat.

Good luck,

Bill Lomenick

[metros]

If the scratch is deep enough to catch with your finger nail then polishing isn't going to fix it.

What about reclearing the diffuser? A lot of people end up clear coating carbon as it gets faded.

[wleehendrick]

I would think you could fill the scratches with the special resin and then sand and buff it out like you would do with gel coat.


If the scratch is deep enough to catch with your finger nail then polishing isn't going to fix it.

Yeah, I need to fill some of the scratched, just need to find the right material. From there, polish, etc...

Thanks,

Lee

[riptide motorsport]

Carbon fiber is lyed up just like fiberglass, get some fiberglass resin and fill it in.

[DodgyTim]

You really should match the resin to the original, but knowing which one is difficult
It is likely to be an epoxy, and you need one that is clear
I've used this one from polymer products
http://www.ebay.com.au/itm/EPOXY-RESIN-HIGH-PERFORMANCE-VERSION-OF-MAX-CLR-24-OZ-/310187764669?pt=LH_DefaultDomain_0&hash=item4838a1abbd&_uhb=1
For coating carbon parts that have come out of a mold and needed a coat to "gloss" the surface, which is similar to what you are trying to do
If you end up coating the entire piece to cover sanding marks, be really thorough and make sure to get the surface surgically clean. I didn't on a carbon piece, the resin went on and covered well, but during the cure it dimpled away from a couple of spots where there must have been some wax, which ruins the look
Hope this helps

[wleehendrick]

Thanks guys, just what I needed. The scratches are small, and a lot of people wouldn't bother, but it's my wife's baby. It would be silly to replace the part (at well over a grand) but I just want the damage to be unnoticeable from 5' away. Already got a quote from to body shop. The insurance adjuster's coming Wed to look at it and sign off. As soon as that's done, I'll get to work on it.

[temperacerguy]

Carbon fiber is lyed up just like fiberglass, get some fiberglass resin and fill it in.

OK, I have never posted here before, but I have to say that this is JUST WRONG!!!

Fiberglass resin is a polyester based resin which will yellow and fade over time. It also is far too brittle for carbon fiber.

The correct material to use is epoxy resin. Most boat building supply companies will have clear epoxy resin. For this repair, you need a clear surfacing resin. West makes a good one.

If it has not cracked, then:

Mix up a small batch of resin (follow the ratio exactly, and either by weight or volume depending upon the instructions)

Place the resin into the deep scratches (I use a syringe I pick up from walgreens)

Use a heat gun to get the resin to flow into the crack and pop the bubbles in the resin

Let the resin cure.

Sand the repair flush

Clear coat using a 2K clear (NOT A RATTLE CAN CLEAR YOU GET AT THE AUTO PARTS STORE). You can get a 2K clear in a rattle can for spot repairs from Spray Max. It's called "Glamour clear" and has a catalyst you inject into the can.

Once the clear is fully cured, polish out like you would with normal paint.

[wleehendrick]

Thanks for the detailed process... should get the check from the ins co soon, and then I'll give it a shot.