Carbon Fibre - Rear Wind-Diffuser - Part I

With the mould looking pretty good it was time to look at the different types of carbon-fibre covering to wrap it in. There are dozens of stick-on imitation carbon sheets available, but I didn't want it to look fake even under close inspection so I had to go for real stuff. I've seen people making real carbon parts for ages and it doesn't look too hard, but the price of it used to be outrageous. Not any more it seems, as I've found sheets of all sizes of raw carbon-fibre on eBay, often being cheaper than vinyl stick-on sheets of the same size! My diffuser is about 60cmx40cm and I didn't want to worry about matching the weave up with separate sheets, so I went for a half square-metre to cover it in one go, which worked out at £19.50 delivered for 100% twill-weave carbon, whereas the 3M-vinyl sheet that contains no carbon at all [but does look a LOT like it] was £27.99 delivered - nearly a tenner more expensive! Needless to say I went for the real carbon - from a firm called [grp_supplies], unfortunately no longer trading under that name and I can't find the new one on eBay :(

OK, so I had to buy some clear epoxy-resin to set the real fibre as well and it turned out to be dearer than I imagined. I could only find small tubes of the stuff for less than ten quid, but the amounts [and the cost] jumped up massively after that. I needed quite a bit for the diffuser too, so I grabbed the best deal I could find - 1kg of resin and 0.5kg of hardener for £28 delivered, which was good value even though they arrived in unmarked and unsealed bottles. They work great though - from a firm on eBay called [CreativeResinSolutions].

I originally intended to just cover the stiff plastic mould and re-fit it, but the carbon provides its own stiffness so the weight of the tough plastic van-undertray just seemed unnecessary. The thick plastic must weigh a couple of kg on its own so even the spaceship-light carbon would be a useless increase and the back end is already well planted with that soundsystem...

This meant I had to get the carbon off the plastic after it had set, which turned out to be stupidly simple. A professional would, of course, produce a fibre-glass cast of the part and use it as an inward-mould for the carbon. Not only would this mean forking out more money, I'd also have to completely re-design the fins on my diffuser so, with the carbon already there, I thought of a workaround, which I'm sure would be howled at by any respectable composite-engineer, but here is how I prepared the mould - after a few tests on a small dash-panel [here] I found this to be the easiest way of quickly fabbing up my carbon part :

PROCESS:

1. Smear the part in a thin film of vaseline. Apply a layer of cling-film to the part, sticking it in place with the vaseline. Repeat the process for several layers of cling-film.

2. Mix a good chunk of 2 parts epoxy resin with 1 part hardener and wait about 15 mins. until it starts to go tacky.

3. Paint a thin layer of the epoxy over the cling-filmed part.

4. Slowly drape the carbon-fibre sheet over the part and press it into shape. The tacky resin should make it easier to hold things in place. Tightly fold the fibre over the edges of the part and tape them in place on the back.

5. Mix some more epoxy-resin and immediately paint a good thick coat over the part, leaving it to dry for at least 8 hours.

**The part should pop easily off the mould by this point once the edges are trimmed and most of the cling-film can be peeled off. You can keep them together until the part is finished, but there is probably a higher chance of it bonding to the mould.

6. Give the part a quick sand with some rough paper. Remove any sharp points, resin drips and bumps. Don't worry about making the surface too even yet, but try not to go down into the carbon.

7. Mix more resin and apply another thick coat to the part, leaving it to dry for at least 24 hours this time. [One nice, thick coat should do it, but repeat process 6 & 7 if it looks too thin or uneven.]

8. Sand the part down to an even[ish] coat, then use finer grade papers to give it a smooth surface and apply the finishing touch to best show off the weave - either a coat of normal car spray-lacquer for the wet-look, or using T-cut / rubbing-compound to buff it to a dull racing-car shine.

As you can see I only got as far as the final coat. I've rubbed it down a bit, but still haven't found time to finish it, so I'll have to cover that in another post.

All things considered though, not a bad try for a beginner! It certainly looks the part - the carbon weave looks very authentic, but the dodgy moulding technique does have it's pitfalls. The heat of the epoxy drying causes bubbles in the cling-film to expand, which doesn't affect flat areas, but has made the back-edge of the diffuser a little sloppy round the fins, although it has given the skinny fins a nice rounded profile. A pro-diffuser would cost most of a grand remember, so for about £20 and a couple of afternoons work I think its turned out superbly! We'll have to wait and see if its a go when its finished and fitted.