Just trying to find out if there's any reason why you cannot do a hand layup in a silicone mould (in this case epoxy / carbon fibre).

All I tend to see in searches are silicone moulds being used to cast solid resins or plasters.

Silicone would be the perfect material to make a mould from the object I want to duplicate (although, there are no complex curves or fine details)  and ideally I would use the mould to make both a plaster 'buck' for vac forming and also do a carbon fibre hand layup.

The issue with silicone is its extremely low surface energy, so you will find the resin will bead up a lot and pool in the low areas, and the carbon won't stay where you put it. You can't use vacuum to hold things in place either  so it all tends to result in very poor quality components.

Can work for some things though, depending on the shape. Sometimes a second silicone matched mould can work to hold the carbon in place. In general though, it is not a cheap material and it doesn't work well, hence why it isn't common practise.

Thanks Hanaldo, since I posted this I was told by one supplier that it can be done :-o   The part I am duplicating is a very simple shape with gentle curves, almost like a small boat hull.
One idea I have had is laying up one resin layer and stick on the cloth onto the original form, ala a skinning approach, and then apply a clear coat and press the silicone mould over that.

I have one part so far that I made entirely by skinning it onto the original and removing it, which worked quite well except for all the sanding needed to smooth the outer surface.