Working with fiberglass requires safety precautions. You must wear a respirator, and there must be adequate ventilation where you work with this material. I do not say this lightly. Fiberglass gel coat and laminating resin contain proprietary polyester resin and styrene monomer, the vapor of which is quite harmful and flammable. Without adequate ventilation and a fitted National Institute for Occupational Safety and Health (NIOSH)-approved respirator, you could quickly find yourself up to your chin in floor. That being said, I love this stuff! But then, I have a terrific respirator and a super ventilation fan in my shop.
As a casting material and mold material, fiberglass is outstanding. You can even use it as a mold material for baking foam latex in an oven in less time than it takes using a stone mold. It is extremely lightweight and very tough. I was really
leery of ever working with fiberglass until Neill Gorton convinced me that it is really easy to use. He was absolutely right, and if I can make it turn out well, anybody can!
The process is somewhat similar to making a stone mold in that a detail layer is brushed onto the sculpture first and allowed to set before adding laminate reinforced layers. However, that’s pretty much where the similarities end. Compared to Ultracal, fiberglass weighs nothing. A thin (1-inch—2.5 cm), burlap-reinforced two-piece case mold made of Ultracal for a 360o head and shoulders bust may easily weigh 20 or 25 lbs. A thin (%-inch—7 mm) fiberglass mat – or fiberglass cloth-reinforced two-piece case mold made of fiberglass for that same head and shoulders bust will weigh maybe 5 lbs., tops! If that much; maybe only 3 lbs. My point is that a fiberglass mold won’t weigh much. This makes for far easier handling and much quicker curing times when you’re making foam latex appliances, and time is money in this business.
Unlike silicone, latex, or urethane rubber molds, fiberglass is relatively inflexible. That is, it will not "give" in the way those other materials will. At least, it probably won’t give as much or at the points where you want it to. In fact, compared to those materials, fiberglass is downright immobile. If you make a fiberglass mold of a hard or rigid object that has undercuts of any kind, you will find yourself with a mold that you cannot remove without breaking the mold, the sculpture, or both. Seriously, even a seemingly insignificant undercut will wreak havoc. Be very, very careful before building a fiberglass mold.
In addition, and I cannot stress this point enough so I’m saying it again: Fiberglass resin is very toxic in its liquid state. You need to work in a room with good ventilation and wear a NIOSH-approved respirator. Serious respiratory problems or death are considered to be unattractive life choices, so I suggest you try to avoid them whenever possible.
Another significant difference between making a stone mold and a fiberglass mold is the size of the dividing wall you will need to build. Because you will be creating a fiberglass flange wide enough for you to bolt the two (or more) sections of the mold together, the clay wall will need to be wide as well.
Why do the mold pieces need to be bolted together? That’s an excellent question. Though the fiberglass mold you make will be very strong and stiff, it will be thin, and because it is thin and also fairly large, there will be flexibility. By bolting the pieces together around the mold flange, the flexibility is taken out of the equation, making the mold very firm and holding its shape for casting inside it.
To build a fiberglass matrix mold of a bust, you’ll need the following tools as well as materials listed at the beginning of this chapter:
WED clay or other water clay
Fiberglass mat, etc.
Laminating resin
Water spray bottle
Clay tools
1-inch chip brushes
Utility knife
Petroleum jelly
Epoxy Parfilm or Synlube 531
Wood base
Polyethylene sheet
Fiberglass gel coat is thicker than the laminating resin (polyester) used to apply fiberglass mat and fiberglass cloth, though some fiberglass resin is considered
all purpose or general purpose. If you decide to use an all-purpose resin, you might find it helpful to thicken it with a filler such as Cab – O-Sil (fumed silica). It will need to be mixed thoroughly and left for a while to ensure that all the fumed silica particles dissolve and disperse throughout the polyester resin. Finding the right gel coat and laminating resin should not be too difficult, but the listing of suppliers in the appendix might be helpful if you cannot easily find what you are looking for locally. Most suppliers have online ordering capabilities and shipping.
Gel coat is available in different colors, so don’t let color selection confuse you. Though there are differences in polyester formulation for laminating resin, mostly in terms of stiffness or surface finish after cure, those properties will not conflict with whatever gel coat is used.
A note about using fiberglass cloth vs. fiberglass mat: Fiberglass cloth is strong and is often used where it could be visible and where aesthetics are important. One of the downsides of fiberglass cloth is that because the strands are neatly woven, the layers do not intermesh as they do with the loose, disorganized strands on the fiberglass mat. Therefore the layers of cloth sit on top of one another rather than meshing together the way they do on the fiberglass mat. This might or might not be a concern for the type of mold being made, but I’m putting the information out there for you to weigh. Fiberglass tissue is very thin, very fine fiberglass mat and is sometimes referred to as veil. It is outstanding for reinforcing and laminating fine detail areas.
Fiberglass resin contains styrene, which reacts with the glass fibers in the fiberglass mat, cloth, and tissue, softening it (essentially dissolving it) so that it is
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easy to shape and mold around forms. Styrene is the primary reason for using proper ventilation and wearing eye protection, rubber gloves, NIOSH-approved respirator, and even coveralls.
The principal health effects due to styrene exposure involve the central nervous system. These effects include subjective complaints of headache, fatigue, dizziness, confusion, drowsiness, malaise, difficulty in concentrating, and a feeling of intoxication. The International Agency for Research on Cancer (IARC) classifies styrene as a potential human carcinogen. Acute health effects of styrene are generally irritation of the skin, eyes, and the upper respiratory tract. Acute exposure also results in gastrointestinal effects. Chronic exposure affects the central nervous system, showing symptoms such as depression, headache, fatigue, and weakness, and may cause minor effects on kidney function. Additional information about recognizing occupational hazards and health effects associated with styrene can be found at www. osha. gov/SLTC/styrene/recognition. html.
I know these warnings make working with fiberglass sound rather frightening. It really isn’t. However, I would be remiss if I did not identify potential problem areas so that you can easily avoid them by working smart and being safe.
For the best step-by-step instructions for creating a fiberglass core (positive) and fiberglass matrix mold, I strongly recommend purchasing Neill Gorton’s four – DVD series, Creating Character Prosthetics in Silicone. Neill is a great teacher and the series is terrific.
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In casting core positives or even when making molds, it is often desirable to add some kind of filler to the polyester resin to give it added strength and longevity. Depending on the need, there are different fillers that will give different properties to the materials they’re added to. For example, adding fumed silica (Cab-O-Sil®) as filler to a material such as polyester laminating resin will cause the silica to act as a thixotropic agent, making the laminating resin thicker. It also enhances tensile strength, abrasion resistance, and stiffness. Adding chopped fibers to that same laminating resin will make it stronger as well. Metallic powders can also be added as fillers. These will make a material stronger as well as heavier; heavier metal powder will add weight proportionally by volume as well as tint the material to the metallic color. Other fillers, such as certain types of microspheres, not only can add strength to a material, they can make it lighter, depending on what the spheres are. Aluminum powder added to polyester resin for fiberglass mold fabrication, for example, will increase the hardness and abrasion resistance of the surface.