Does the material with which I make the mold for carbon fiber parts affect the finish the part will get? If it does, I would like to understand how a given material may affect the finish.

Another thing that is confusing me is the exact definition of finish. Does it refer only to the smoothness of the surface of the final part, or does it also refer to gloss and polish?

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    – user16
    Jan 26, 2016 at 14:41

1 Answer 1


The finish of the mould will certainly have an effect on the finished part. How much of an effect depends on the exact process, for example if you use a gel coat then that will pick up the surface texture of the mould pretty closely. Without a gelcoat the ratio of fibre to resin will determine how much the weave of the fabric comes through.

In this case it's not so much the mould material as such as the finish of the mould surface and of course any release agent used will have an effect as well. It's certainly possible to get a glossy part straight out of the mould as long as t is prepared properly. In practice you would balance the time and expense you put into maintaining the mould with the amount of time spent on finishing the part after it comes out of the mould. eg if you are making dozens of parts it might well be worth getting the mould as close to perfect as you can to save time spent finishing each part. If you're just making a one-off you might not worry so much about the mould finish and sort out the finish on the part itself.

Another consideration is that for high performance laminated parts you may find that the optimum resin to fibre ratio is just enough to wet the fibres and you get the weave of the mat showing through regardless of the mould finish.

In terms of definitions finish can refer to overall surface smoothness as well as gloss as these are really just two aspects of the same thing. This is a significantly different thing from the geometric accuracy of the surface.

Similarity low volume moulding processes like silicone, plaster etc tend to be more likely to pick up small surface defects than an CNC machined steel mould.


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