Carbon Fibre Frame Repair

This post is about the repair process I carried out on a 2007 Scott Genius MC30 Frame using a wet lay up technique of Carbon repair. The story behind the damaged frame is that the owner had the misfortune to drop the bike twice on a rock in the same place. Resulting in the de-lamination of the inner layers of the carbon sheets approx a 1/3 of the circumference of the tube. The area of the damage would flex under external pressure rendering it useless.

There were a few options available, one to renew it at great cost or to send it off for professional repair (very few about) which could have been time-consuming and expensive or attempt to repair it yourself.

As an Engineer by trade and a keen hobbiest as a kid I thought I would give it a go attempting the repair for myself. The kit I sourced would be ideal for the DIY enthusiast as the instructions provided were simple to follow resulting in a satisfactory serviceable repair being achievable. Clearly the level of finish will depend greatly on the skill of the person carrying out the repair.

The repair kit used was from a company called carbonology and cost approx £40. The specific kit was kit size B. The kit included all carbon crossply sheets, resins and instructions etc. I did however modify the repair process specific to the job I was to carry out.

Making good the damage -

First of all the crack and surrounding area had to be sanded to remove all the frame lacquer from the carbon fibre beneath, making sure not to sand deeply into original carbon fibre. From the photo you can see that I sanded into the area of the seat post. The reason for this was to add extra strength to the repair by taking the new layers into the that area, this would also minimise the visual impact of the repair – avoiding an obvious bulge had I not done this.

Next, was to make sure the crack would not get any larger, to do this two 5mm stop holes were drilled into the frame at either end of the cracked carbon. Then I drilled a 13mm hole into the frame to allow the injection of expanding foam, this would support and strengthen the repair from inside the frame tube. Once the foam had set I then I carried out the filling repair to the excessively damaged area of the tube. This would need the use of Epoxy Resin, Hardener  and a high density compound mix. Sanding and refilling would be carried out to ensure the profile of the tube matched that of the surrounding area.

Preparing the carbon sheet -

Once complete then the first stage of the carbon to be layed up could be carried out. This part is a little tricky and some patience is required (measure twice, cut once!!) as a stencil needs to be cut out of paper ensuring there is an overlap on the underside of the frame top tube, also two tongues that lay into the seat tube had to taken into account ensuring they matched from both sides. Using the stencil the first layer of carbon could be cut ensuring the it lays >40mm beyond the crack towards the Headtube. Be very careful when cutting the carbon sheets as the lattice can easily break away. Finally, cut an area of Peel Wrap that will cover the carbon sheet when layed up.

Laying up the carbon sheet -

Using the supplied safety kit, mix enough of the Epoxy Resin and hardener to cover the area that the carbon sheet will be layed on. Lay the sheet on the area to be repaired and carefully move into place. Once happy, re-apply some more resin over the entire area then lay the peel wrap around the tube. Next, apply the shrink-wrap tape then using a heat gun apply heat to the tape ensuring the tape contracts around the tube. Allow to harden. Remove the shrink-wrap tape and peel wrap and sand to the profile of the frame, also refill any pot holes with resin and re-sand where necessary. Repeat the process with a further two layers of carbon fibre making sure each layer is cut back by approx 10mm from the layer before at the end near the head tube, thus maintaining a good profile from the original tube to the repair layers. The last layer I avoided using the heatshrink tape as I found this would disfigure the layer of carbon. So with the last layer I used only a Peel wrap and made sure that every hole was filled and lump sanded resulting in a perfectly profiled tube before finishing.

Lacquering -

The final process was to lacquer the repair. This was completed with two layers of car body clear lacquer sanding lightly between coats. Also ensuring a good overspray was carried out into the existing frame and any unwanted overspray polished out. This resulted in a job that surprised me and my friend whom I repaired it for. The frame is still going strong after many hard rides and shows no signs of fatigue.

If you would like any more advice on how I repaired this frame or have a frame that requires repairing then contact me by email – greatb2@hotmail.co.uk

Photo screenshow of the repair using Flickr can be seen – here