It will sound abnormal to most of you, but I would like a painted part...

I would like to achieve a bonnet finished in a plain colour in order to match the other body panels.

The use of carbon fiber is in my case is just for saving weight.

What options do I have ?  may I use a "standard" white gelcoat as on fiberglass, or may I paint the part obtained with the normal carbon fibre appearence ? What kind of primer shall I use ? or maybe no primer at all ?

easiest thing is to make the part normally, then get a body shop to spray it for you.  They will know the right primer to use to ensure adhesion to the resin and the top coat.

There is nothing to stop you using a coloured gel coat to spray in the mould like you would with a clear one.  not sure who sells coloured gellcoats suitable for that.  Plus not forgetting it would be hard to get a colour match to an automotive paint.

Hi Anatole,

I'll second what Warren posted, you can use a coloured gelcoat - you would want to use an epoxy compatible polyester gelcoat (like our GC50) which you can pigment using any polyester pigment. It would be difficult to get an exact match to an automotive paint unless they've used a standard RAL colour (even then it might be tricky to be exact) but pure black for example might be more realistic.

If you go down the paint route, which is probably going to be best from a colour matching perspective, then you wouldn't bother with a gelcoat on the part, just spray the bare carbon surface. Spraying composites that don't have a gelcoat is MUCH harder work that spraying ones that do because everywhere the actual fibres are touching the surface of the part (undetectable by eye but the paint will soon find them!) then you'll get a fish-eye or pin hole. There are special spraying techniques which those who work with carbon fibre a lot start to develop but there's really no substitute for spraying, flatting, spraying, flatting until the surface is right.

Before spraying, you would want to prepare the surface of the carbon with an abrasive pad or fine abrasive paper to ensure a good 'key' for the paint and to remove any traces of release agent. Like Warren says, a professional spray shop will have experience of this but it's not out of the question to do yourself if you have a spray-gun and compressor.

I hope this helps,

Best regards, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales