HOW TO... Repair carbonfibre
More and more modern cars contain this miracle weave of carbon strands encased in epoxy resin. Sometimes it’s nonstructural, there to save weight or give the right motor sport-flavoured message. Other times, a hefty carbonfibre moulding forms the structure of the car itself.
And sometimes, epically strong as carbonfibre can be despite its extraordinary lightness, it gets damaged. Then what?
It used to be said that once damaged, a carbonfibre component had to be thrown away. That would be very bad news for owners of carbonfibre classics-in-waiting. Would new components be available in the future? Would the moulds still exist?
The truth is that carbonfibre can be mendable, even around structural hotspots such as suspension mountings. The repair will be visible if the component flaunts its weave, but if it’s painted, or hidden, that doesn’t matter until future discussion of originality rears its value-decimating head.
This is how a carbon-literate bodyshop does it. Tapping with a hard metallic object, and listening for a dull thud instead of a chirpy resonance, reveals the extent of damage beyond what is seen. It needs to be ground away. Next, the edges of what remains are ground at a shallow angle, revealing a half-inch band of each ply. The edges of each ply layer are then traced onto clear plastic film to act as templates for sheets of new carbonfibre cloth, and the direction of the plies marked on each.
Now the right kind of epoxy resin is mixed in exactly the right ratio by weight, otherwise strength will suffer. This is spread on a large sheet of clear plastic, the first layer of carbonfibre is laid and more resin poured on top, followed by the first template film. The ‘sandwich’ is now squeezed to remove air bubbles, more resin is painted around the edge of the original component’s hole, the lower plastic sheet is removed and the now-sticky black sheet placed over the damage site, its fibres in perfect alignment. This process is repeated for all the other layers, each thin film removed before each layer is added.
Finally, the repair is warmed to cure it, and preferably ‘vacuum-bagged’ during curing to pull out any remaining, strengthsapping, tiny air bubbles between layers. A tap-test to check for a uniform sound, smoothing-off, painting, job done. Which should make owners of McLaren F1s, Ferrari F50s and all that followed very happy indeed.