Fiberglass Moulds

Fiberglassing requires the following safety precaution:

- There must be adequate ventilation, as the vapours produced are harmful and flammable

- You must wear a respirator, and gloves (preferably 2 pairs, as this way a layer can be removed if necessary, and you have more protection from glass splinters)

 

Fiberglass is extremely lightweight and very tough. Curing times when making foam latex is much quicker than stone moulds or ultracal. Compared to other mould materials, it is relatively infelxible, if you make a fiberglass mould of a hard or rigid object that has any undercuts, you will have a mould which you will not be able to remove without breaking the mould, sculpture or both. Mould releases for fiberglass are mirror glaze or mould wax release. These should be painted onto the core after talcing. The talc can help act as a visual indicator.

 

Layup/Laminting resin: - is cheap, polyester resin that is slightly blue in colour. You need 2% catalyst to the amount of layup resin used.

 

Gel coat: is a thicker polyester resin which is slightly pink in colour. Again, needs 2% catalyst. Acetone is the only solvent that can break down polyester resin, and can be used to clean the brushes during/after application.

 

MEKP (catalyst): organic peroxide catalyst. Always weigh out 0.5 more than you need; e.g. If you need 4grams weigh out 4.5grams. 

 

Different types of fiberglass

 

Loose chop strands/choppies: can mix with resin to make a filler

 

Chop strand matting: matting bound by starch

 

Vale/Fine surface tissue: is the same as chop strand matting but a lot finer.

 

 

METHOD

 

• Pour the catalyst into the gel coat and mix. It should turn a brown colour. Brush on this coat, which will pick up all the small details and constantly look at it from different angles to be sure the whole piece is covered. Try and ensure there are no air bubbles, as if foam latex was used in the mould, it would expand in the oven and crack the mould. The work time for gel coat and layup resin is about 20-30 minutes. Leave the gel coat for 20 minutes and then check with your finger to see if its tacky. Its needs to be tacky so that the next layers will bond to it. If its completely dry, mix some more gel coat and catalyst and do another coat so that it can dry tacky. Then add the catalyst to the layup resin and mix it. Decant some of this mix into a seperate cup/container, and make a mud/porridge but mixing it with some talc in a 50/50 ratio. Then paste this with a stick into the gaps where the keys are. This is done so that the matting can lie better, rather than having it try and contort around awkward shapes. Once this is done, using a brush, dampen the sheets of chop strand matting with the layup resin and apply it to the piece. The resin attacks the starch, making it more maleable to work with. The matting can be torn up into smaller pieces and to help create more of an overlap between the fibres, creating a stronger mould. 2 layers of chop strand matting is about enough for a facial prosthetic, more will be needed for bigger pieces. You can brush the resin over the matting once its sitting on the mould to help shape it to the mould better and to chase out any air bubbles (to "knock it out").

• For a final layer, vale can be used which gives the mould a smoother exterior. It also helps soak up excess resin, shows you have pride in your work and a professional curteousy. 

• The mould should be cured in a couple of hours but ideally should be left overnight. It should pop straight off the core. 

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• 6mm holes then need to drilled in every touchdown point before all the clay is scraped out of the mould. This is so the positive will fit back in perfectly when running the piece.  Holding the mould up to the light can make it easier to see where to drill, as identifying the touchdowns can be difficult with a thick mould. At this point you could also drill a hole in the positive face in order to make it an injection mould. 

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• The edges of the mould then need to be neatened up with a vibrosaw, as typically there will be fiberglass poking out which is hazardous. I also used a mechanical sander to help really smooth down the edges of my mould, as, with it being a slightly awkward shape, it was quite spikey. 

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• Then clean all the clay out of the mould using lighter fluid, and keep it so you know how much silicone/gelatine/latex you will need to fill the mould.

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• Foam latex will inhibit the curing of silicone, so after using foam in a fiberglass mould, it cannot be used to make a silicone piece. Vaseline works fine as a mould release when running gelatine or silicone, but you cannot run foam in a fiberglass mould after using vaseline in it.