I use various types of moulds, the conventional mould being made from fibreglass[FG] and polyester resin. Figure 1. shows a mould for a GSXR mudguard. FG polyester moulds are OK for ambient cure lay-up but for elevated cure and prepregs a mould of carbon epoxy will be required because of greater expansion of fibreglass compared to carbon and the higher temperature properties of epoxy.

The mould can be anything to form the required shape, I have used an ice cream container as a mould. The mould must have suitable draft angles so it will release. The mudguard that Figure 1. was the mould for, wouldn't release from a one piece mould so a two piece was necessary, because I like things symmetrical and didn't want a line down the middle of the guard I made the mould in three pieces.

The basics are:

1. Make the plug, with extended edges to allow for trimming of the mould and trimming of the parts made in the mould. Make sure the part will release. Remember the larger the radii the easier it is to get fabric around a corner and complicated compound curves can be awkward to lay up.
2. Paint and polish the plug, even though it is to be polished and have release agents on it use paint that doesn't react with polyester, I use polyester spray filler. Finish the plug how you want the final article to be finished i.e. if you want a mirror finish that is what the plug should have.
3. Release agents, I use TR general purpose release wax, I am told a good floor polish is the same. According to the tin a plug should be waxed and buffed 5 times. After early attempts stuck I now wax it about 20 times, just to be sure. Then I give it a few more coats of wax and buff each one.
4. If the mould is multi piece you will have to form some edges to make the flanges, people use wax well they sell wax labeled for this purpose, I do this with plasticine. You have to be gentle when putting the first few layers of fibreglass on but it seems to work.
5. The layers will be something like

• Gel coat.
• FG tissue
• Three thickness' CS mat, separate strands put in sharp radii to make sure no voids exist.
• a couple of layers of woven mat
• Extra woven mat on bolt flanges
  

6. Before you start mixing resin, plan what your going to do, how many layers of chopped strand, any other reinforcements, core materials, make sure you have tools and cups to mix the resin in. Then cut out the reinforcement.
7. Paint a coat of gelcoat on the plug, I do this between item 5 and 6, leave it until: when you stick your finger on it, you don't get any on the end of your finger. Then put a second layer of gelcoat on.
8. Mix the polyester resin in batches, I mix about 75-100 cc at a time, this is the amount I can use before it starts to gel. Lay up the layers in the order in item 5. I only use 1 cup, you can keep mixing in the same cup you don't get any lumps in it.
9. If the mould is a split mould leave the first piece to cure for a day or so before removing the barriers used to form the flanges. Paint PVA on the flange, lay up the remaining pieces as you did the first bit.
10. Let the mould cure for a couple of weeks, if postcuring leave for a couple of days then postcure. If its a split mould drill 6mm holes in the flange for the bolts, before releasing from the plug/mould. Then release from the plug. You might find it easier to trim the edges before releasing. If you have a lot of trouble getting them apart you can bang on the mould or use an airline, but be careful you don't crack the gel coat.
11. Any imperfections in the surface can be sanded out and polished back up, I use Solvol Autosol which is an aluminum/chrome polish. I see the FG catalogues have Faranclea[?] G8, I use that on paintwork but it doesn't do a lot to gel coat, metal polish seems fine though.
12. Release agent, like in item 3 I use TR release wax, again I don't want any sticking problems so I wax the mould lots of times.
13. If your vacuum bagging in a bag, rather than sticking the bagging material to the edges of the mould. Its a good idea to sand the edges and the back of the mould to prevent puncturing the bag. I stick breather cloth around the bolts to prevent them puncturing the bag and also tape up the edges.
14. If your bagging and sticking the bag to the edge of the mould, You might find it quite helpful to stick a vacuum fitting into the mould itself see inset Figure 3. I drill a 5mm hole in the mould and glue a 2" piece of Cu brake pipe in it, with bit of 5 min epoxy. The same can be done for a vacuum gauge port. The bag you make is much simpler to handle if it doesn't have any fittings in it.
15. You are meant to leave the mould to cure properly for a couple of weeks before use, I have used one a few days after it was made and there weren't any problems. Generally I don't have any problem waiting a few weeks before first use but if this time is a problem, it can be reduced by an elevated temperature "post cure"

It is better to rip chopped strand, rather than cut it. If you cut it you get steps in the laminate.

I keep FG mat in plastic bags, these bags tend to have a lot of loose fibres in them, I use these fibres to fill sharp corners. In particular the corners formed where a flange is being built up.