Im trying to make a carbon fibre bonnet but am stuck with the matting not being wide enough.. is there a special technique to lay is so when you pull it out of the mould there is no visible join on the surface?

If you are overlapping 2 sheets of carbon in a mould for resin infusion (or similar) in say a "V weave" pattern, then you should not get a physical bump or line once complete on the moulded side.  You will get a slight hieght difference on the reverse peel ply side.

To get the weave to seamlessly go over a overlap join would be very very hard to do perfectly. It would be easier to make a feature out of the join.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant