Carbon Fiber Cracks

**ZL1Mike** · 03-04-2021, 07:09 PM

Hello everyone,

I was looking over my carbon wing and noticed some cracks. I was wondering if any of you had experience with repairing carbon fiber. I can’t tell if the cracks are in the coating or fibers. Also, is it likely that the cracks will spread if I don’t repair them? If possible, I would like to repair the wing because a new one is about $1300

Thanks

**Sizzle Chest** · 03-04-2021, 07:48 PM

Your CF wing has a clear coat on it...

If it is cracked, it would need to be sanded down and re-cleared I'm afraid.

**dgage** · 03-04-2021, 09:14 PM

It doesn’t look like a crack in the carbon fiber so much as the outer coating. Usually carbon fiber (composite) is done with epoxy or similar resin and it looks like the coating isn’t handling the flexing. Not sure why there would be a crack or flexing in the second picture so maybe that’s a scratch? The first picture shows a joint and I’m sure there is some flex there and the coating isn’t handling it. I’d recommend looking at an epoxy coating that can handle some flex. The problem is, I’m not sure how you’d repair it to make it invisible. You’d really need to figure out the coating so you can get something that would chemically bond with the existing coating and hopefully be an invisible fix. But the repair definitely needs to handle some flex.

**psnt1ol** · 03-04-2021, 10:03 PM

I made custom subwoofer enclosure with carbon fiber skin as well as carbon fiber car parts in my younger days. I dealt with hairline cracks on several occasions.

You have to sand it down then reapply the resin. Generally, you would want to do 3 to 4 coats and wait several hours between each coat. After it cured...sand it till the repaired area is level to the surrounding area. It is just like fixing a touch up paint blob from this point forward. go through your progression of sand paper to around 2500 then polish with a DA.

Its a long and slow process but when its done right...you could hardly tell it was there from a few feet away.

The following vid would give you an idea on what I am talking about. Good luck.

**Coatingsarecrack** · 03-05-2021, 03:16 AM

Yeah those cracks looks like they are in the resin.

Psnt is right and you may notice where you spot repaired but probably only you will notice.

Second one on the end looks to be on a edge. Could be a scratch but I’m thinking stress scratch

Sent from my iPhone using Tapatalk

**ZL1Mike** · 03-07-2021, 08:08 PM

The crack in the second picture appeared randomly after sitting on my table for a couple of weeks. I haven’t been near the wing, which makes me think that it might be a stress crack. Will I have to apply clear coat to the new resin or does it act like clear coat?

**psnt1ol** · 03-07-2021, 09:14 PM

before you do anything... wet the area in question. While wet, see if the appearance of the cracks lessen. This is most likely how it would look after the repair.

The only reason why you would add a few coats of clear is mainly for UV protection (so that the resin wont yellow as it age). You could accomplished this also with a coating that has UV blocker or a diligent sealant maintenance schedule.

**ZL1Mike** · 03-08-2021, 02:48 PM

Originally Posted by psnt1ol

before you do anything... wet the area in question. While wet, see if the appearance of the cracks lessen. This is most likely how it would look after the repair.

The only reason why you would add a few coats of clear is mainly for UV protection (so that the resin wont yellow as it age). You could accomplished this also with a coating that has UV blocker or a diligent sealant maintenance schedule.

I didn’t see a big difference after applying water to the cracks. So, would Cquartz UK prevent the resin from turning yellow?