So after my jaunt the other week, my mate noted a large gouge in the back rim. On closer inspection there was a rough hole about 3mm across punched through the rim wall, in the middle of the gouge. I've no idea what caused this - I certainly wasn't aware of smacking it off a rock. I think it may have been a rock pinging up off the tyre and hitting the rim. This happens often but I guess in this case the rock had a particularly jaggy bit which did the damage. Slightly frustrating as I've used these rims on a lot of very hard terrain and apart from lots of scratches, nothing like this has happened before. I guess it's the trade off for using carbon fiber. It's light but more damage prone than aluminium.
The rim wall is very thin here - you could flex it with your thumb either side of the hole. We plugged it with epoxy for the ride home but my mate (who fixes canoes and kayaks for a living and uses carbon fibre a lot) suggested doing a patch repair to be on the safe side. He kindly gave me some carbon sheet and some epoxy resin, as well as advice.
The damaged area filled with epoxy. I decided to leave this as is.
Remove a couple of spokes, clean the area up and give it a good going over with emery paper to roughen it up and allow the epoxy to key to it.
This is where it gets tricky. The carbon woven sheet is tricky to deal with as it comes un-ravelled very easily. To cut it you need finely serrated (and very sharp) scissors. I used my Wengen Swiss Army knife scissors and carefully cut three sheets of increasing size. You then mix the epoxy, which is very runny, unlike Araldite, and paint on the area to be patched. Lay the first sheet on carefully and then dab it down with a plastic spoon until the resin has soaked right through. Then dribble more resin on, add the next patch, repeat.
The sheets and resin need to be pressed firmly down with no air bubbles. I used sheets of cling film at first stretched over the patch and then wrapped round the rim. It all moves around a fair bit, but this is fine. The keen eye amongst you will note the patch extends over two spoke holes. This is probably well OTT but it weighs very little so I consider this to be a belt and braces approach.
This was the clever bit - wrap with insulating tape as tightly as you can. Excess resin was squeezed along and out the end as you did this. This is wiped up, along with some that had run into the rim bead. You then leave it for 48 hours.
Quite pleased how this came out.
Smoothed down with course to fine emery paper. I'd cut the excess carbon sheet away from the edge of the rim but after sanding this was a bit ragged. So I painted over with glass fibre resin as a gel coat, then smoothed some more, followed by a light over spray of clear lacquer.
The finished article. Re-drilling the spoke holes was slightly stressful but it went OK. Its a bit rough but I'm not bothered about that. time will tell if it works!
