The chemicals used in the prop room fall into six general categories: poly vinyl acetate (PVA), foams, thermosets, thermoplastics, molding and casting rubber, and solvents. We'll deal with them two at a time over the next three issues.
Some of these chemicals are perfectly safe to use. Most are safe when used with precautions. A few are dangerously poisonous. As we take our excursion through the prop-building laboratory we will point out some of the dangers and steer you away from the most toxic.
White glue - PVA has been formulated into several well-known white glue products, some water soluble and some that are highly water-resistant. Most of the trade names are familiar: Elmer's, Will-Hold, Weld-Wood, Weldbond, etc.
Flex-glue - An adhesive used in binding books has found a place in the hearts of prop builders and costumers because it remains flexible after it dries. It never hardens. One product that is packaged specifically for the theatre craftsmen goes by the trade name "Phlex-glu", and is used as far more than just an adhesive. It is employed as a paint binder, a texturing agent, an embedding medium and a coating material. Ford Davis of Spectra Dynamics, the manufacturer of Plhex-glu, says he is "in business to help people use the product he manufactures" and welcomes the opportunity to talk to people seeking advice on solving texturing problems.
PVA texture coating - PVA is so good at making textured surfaces that thick formulations are being devised specifically for theatre craftsmen and artists. One such product that has become popular in the last two or three years is "Sculpt-or-coat". It began as a coating to drape and stiffen fabrics, was found to give sculptures carved from foam a tough, smooth surface, and then the product grew in the hands of enthusiastic users to become very versatile. You can write or call Sculptural Arts Coating Inc. for bulletins explaining some of the many ways their products can be used. Rosco Products has recently introduced their own line of PVA coating, and your local Rosco dealer should be able to give you information on it.
PVA sealer - PVA sealer is used by painters to prime coat drywall plaster and masonry before it is painted. This material is now a standard product with painters, replacing polyurethane coatings for making a tough, glossy finish. Sculptural Arts Coatings have come out with a new line of non-toxic scenic paints with a PVA base.
Foamed plastics are so much a part of the stage crafts in some of our theaters that we are likely to think that they were invented for our benefit. The fact is, the bulk of foamed plastic is used in manufacturing -- for insulation, airtight sealing, flotation devices, packaging and for mattresses and cushions. Compared to the bulk of foams manufactured, the entertainment industry is a small user.
Only three products are of major interest to the theater craftsman:
Polystyrene Foam - Dow Chemical owns the trademark "Styrofoam" but several manufacturers are producing expanded polystyrene. This foam is available in two basic forms, easily identified by their colours: white and blue. White styrene foam will burn and is doubly dangerous in a fire: it not only flames but in the process it produces a black smoke containing toxic styrene vapour. Blue foam is flame resistant. A somewhat denser beaded foam of the "styrofoam cup" variety is also available.
Urethane Foam - One factor that adds to the confusion of understanding plastics is that the same plastic may appear in many different forms. Urethane is one such product. It is available as a foam, as an unfoamed solid, as a liquid coating and as a thermoset rubber compound. (The rubber compound will be explained in a future article on mold-making plastics.) Urethane is probably the most useful foamed product to the theater technician. It can be purchased in a wide variety of sizes and densities, in both flexible and rigid form. Two-part kits, to be polymerized and expanded by the consumer are also available.
Rigid urethane foam (often sold as "florist's foam") is widely used in the theater for constructing lightweight stone work and cornice mouldings, in sculpting figures, and making turned balustrades.
Flexible urethane foam (the familiar "foam rubber") is used in the prop room, as it is in in industry, for making cushions, mattresses and padding for upholstery.
The two-part urethane kit consists of two parts which are mixed to make a rapidly expanding foam in a variety of densities. When the mixture begins to foam, it can be poured or spread to make free-form rocks, tree bark and bread stuffs. Or the foaming liquid can be poured into a mould to make very controlled, lightweight castings.
The two-part urethane kit must be used with strict safeguards. In the liquid state these chemicals are dangerous to eyes and skin, so you must protect yourself by wearing gloves and goggles. The vapour produced when you mix the components is toxic, so you must protect your lungs by wearing a respirator and working in a properly ventilated environment.
Polyethylene foam (Ethyfoam) - This foam comes as a round rod in a wide range of diameters from 1/4" to 6". It is flexible and is used in industry as an insulator and sealant. Because of its flexibility, the scene technician finds this product very useful in making curved decoration. He splits the rod down the middle and uses it to make half-round mouldings. It can be split a second time and used to make flexible quarter-round mouldings. A slightly less flexible polyethylene foam is available in sheets of various thicknesses up to 4". It is used for sculpture or scenic construction in situations where the more brittle polystyrene or urethane might be too fragile.
Other plastic foams - I will mention in passing that several other plastics - vinyl, epoxies, silicones, cellosics and phenolics - can be expanded to make foams, each having its own properties. But let's not allow these to clutter our minds. They may be of some interest to the experimental theatre craftsman, but most of us can consider these to be just a little too exotic to bother with.
Parts II and III of Propchem 101 are continued in issues #2 and 3 of Proptology. They will be appearing on this site soon. Information on some of these products can be obtained from:
Ford Davis Sculptural Arts Coatings Spectra Dynamics PO Box 13113 Albuquerque, NM Greensboro, NC USA 87102 USA 27415 phone: 505-843-7202 phone: 800-743-0379 Rosco Laboratories Ltd. Rosco Laboritories Ltd. 1271 Denison St, Unit 66 36 Bush Avenue Markham, ON Port Chester, NY Canada L3R 4B5 USA 10573 phone: 905-475-1400 phone: 914-937-1300 fax: 905-475-3351 fax: 914-937-5984