Fixing Carbon Fibre.
Turbo Mini Forums

I got hold of a carbon fibre bonnet for a princely £65 a couple of weeks ago which I was most pleased about.

Only problem was that whilst the previous owner was driving, a magpie had flown into the bonnet whist he was driving, leaving some nasty, deep spider web cracks in the resin down to the weave.

The guy I bought it off was adamant it couldn't be saved but through prior experience I though it was worth a crack (excuse the pun) and if worst came to worse, i'd either be cutting holes in the bonnet for the intercooler which i could strategically position take care of the damage, or I could what a sticker over it like a bonnet number plate :)

So yesterday I got cracking and popped down to Halfrauds to get some supplies, which were thus:
1x sanding paper
1x rubbing compound
1x carnuba wax
1x sanding block

Other necessary utensils:
2x rags
1x palm sander with fine grit paper
Epoxy resin and hardener

The plan was to sand all the epoxy resin around and including the cracked area down to the carbon fabric (without going through the fabric and ruining the bonnet) before re-applying a new layer of epoxy resin and making the bonnet look good as new.

One bonnet:


Crack from afar


Bad picture of a close-up


Mostly sanded out


Using the rubbing compound to get rid of the sanding marks ready for re-applying resin


Resin applied and drying. Will check tomorrow to see how its turned out.
Please note white mark is a reflection




Still needs another sanding session to get the new epoxy even with the rest of the bonnet, re-compounding and then a polish and wax.

Fingers crossed it works, but so far so good

looking ok tbh
wouldnt have though a crack like that be save able without painting

Yes i moved to the darkside

Instagram @jdm_brett

The problem with doing it is that if you're not careful, you'll end up ruining small patches of the carbon fabric whilst trying to get an even finish by over-sanding.

Consequently I couldn't get all of the evidence of the cracks out because I was already starting to go through the carbon in areas.

Reckon it'll turn out fine though and you wouldn't notice unless you were looking closely.

id be tempted to put alot of lacquer on there and buff it so well all you can see is carbon and reflection

Yes i moved to the darkside

Instagram @jdm_brett

Regardless of how much lacquer you put on, or resin because they're clear you'll still see the tiny air pockets left under the old resin i wasn't able to remove during the sanding process which were caused by the bird.

I am however going to rub down and re-lacquer the whole bonnet, not just the patch.

Good work, but repairing that to be indiscernable to the eye is going to be a bitch; i've a crack in my curley dash (thanks Parcelforce) and know it's a nightmare!!!
But good work though - fair play!

Little update.

After waiting for the new resin to cure overnight, went out and sanded it all out smooth with the rest of the bonnet.

Had a slight issue in that some spots seemed to have rejected the resin (similar to water running off oil) meaning there were about ten of so tiny low spots.



Not a problem though as i just knocked up another tiny amount of resin to build out the low points. This was actually applied using a pencil by just dabbing it into the pits.

Currently still waiting on it to fully cure to make sure the same thing hasn't happened again.



Tomorrow it should be all finished, but it still needs a final sand down using decreasing grades of paper all the way down to the rubbing compound to get rid of any sanding marks. Then a few coats of new lacquer all over. Another final cut with the rubbing compound and then buff til arms get tired.

So another update.

Because it was pissing with rain i couldn't get outside before 3 to do some more work on the bonnet, but I still managed some progress.

The blobs of resin I put on yesterday were sanded back down level before using prep wipes to clean it all up and get rid of any dust etc prior to applying a few new layers of lacquer.

The first layer went down OK but you could still see very faint sanding marks underneath.

After a few more layers however the gloss started to come back and any discolouration disappeared.

It then started to rain again.

A few more layers will be put on again tomorrow all over the bonnet to bring it all up to the same depth of colour before cutting it all again and a very very good polish.

It basically looks as good as new and should look better than new by the time i'v finished.

you've done a good job, probably wouldnt know its there unless you knew

Thats a great save :)

Superb work, £65 + bit of hard work; well worth it!

Cheers guys. Will update tomorrow as and when...

Nice one mate, fair play that's a great result. :)

Good work there.

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


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Good skills

Very impressive, but how did you manage to sand back through the clear coat and not touch the carbon fiber?

A lot of patience and a very fine hand is how to not go touch the carbon.

This is actually the second time i'v bought a carbon bonnet thats had a defect or two. The first one didn't go very well at all and went straight through the carbon into the fiberglass behind, which was irreparable. So i learnt my lesson this time.

I'll post some pictures later if i can showing where i started to sand into the fibres. Once you start going through it can very quickly go wrong

That's a top job mate well done!!

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

That was a good fix, didnt expect my old bonnet to come up like that!

Matt W