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in Liquid Rubber & Plastic for Moldmaking & Casting

No. 25 • Spring/ Summer 1999


	EFX, Displays & Theatre

Polygel® 40 Is No Alien to Success of the Human Body

"The Alien" at Studio One/Mannetron in Battle Creek, MI, set up and ready to have a Polygel® 40 Mold brush applied. Note the plasticene flange with a key groove that creates the parting line between the front and back mold halves. Once the plasticene is in place, simply spray a light coat of PolEase® 2300 and apply the Polygel® 40. When the mold and shell are made on the front half, the plasticene is removed, release agent applied, and the back half is applied against the completed front half. The complete mold and shell can be made in 24 hours.

Studio One/Mannetron of Battle Creek, MI, has used many Polytek® liquid mold rubbers and resins over the years for creating a variety of items for special effects, props, and displays, as well as for a myriad of other decorative reproductions. In most instances where multiple resin castings are to be made, a PlatSil® or TinSil® RTV silicone mold will be constructed to insure maximum mold life, given the harsh conditions expected from resin systems. Although making an RTV silicone mold can be a nice form of insurance, it does not come without its price.

Poly Urethane Savings Can Add Up
     As Studio One has learned, Polytek® Poly Urethane mold rubbers can produce many high-quality resin castings when properly handled. When a Poly Urethane mold is used, the cost savings can be substantial, given that most Poly Urethane liquid mold rubbers are half the price of silicones. Take the 4-foot-tall alien pictured at right with Tom Kipp of Studio One. The master alien was a copy of an original used in the movie The Roswell Incident. A Polygel® 40 blanket mold was brushed over a foam original. Polygel® was chosen because of its ease of use and specific formulation for brushed applications. Polygel® 40 consists of two low-viscosity liquids which, when mixed, self-thicken to yield a creamy, thixotropic consistency ideal for brushing. The 1/4-inch-thick mold was subsequently backed with a fiberglass shell.

The Right Rubber and Careful Handling Make the Difference
     Over 30 polyester resin castings have been rotocast using this Polygel® 40 mold. Studio One believes that the choice of the right mold rubber and careful mold maintenance are the keys to success. Polyester resins are known for their aggressive behavior in any rubber mold. To keep the mold in top condition, the following procedure was adopted. After several castings, the Polygel® mold was soaked in hot, soapy water. This step helps to extract any styrene and other resin chemicals that are absorbed by the rubber during casting. When removed and dried, wax (like Johnson's Paste Wax) was applied and buffed to a thin coat. Polyvinyl alcohol (PVA) was then sprayed into the mold and allowed to dry to create an additional chemical barrier to mitigate resin penetration and damage. A light coat of Pol-Ease® 2300 silicone-based release agent was then sprayed on top of the fully dried PVA to insure that no polyester resin adhered to the surface of the Polygel® mold. When the castings are demolded, cleanup of the casting is a snap prior to finishing, since the PVA can be washed off easily with warm water. Even though the underlying wax coating melts due to the high heat (exotherm) generated by the polyester resin, the PVA barrier prevents this wax from coming in contact with and sticking to the cast part. Any wax on the resin surface would require sanding or some other time-consuming method of cleaning.
     Each component in this process has a very specific purpose. In some cases, all of these steps together may be impractical. In many cases, it may pay to jump right into a silicone mold rubber. For those instances where only a moderate number of resin castings are needed, a Poly Urethane rubber employed with techniques such as these can help alienate unnecessary mold rubber expenditure.


	Tom Kipp with a polyester rotocast Alien and the Polygel® 40 mold behind him. This mold produced over 30 such castings, demonstrating that with proper care and application of parting compounds, Polytek polyurethane molds can produce large numbers of resin castings. Higher-cost silicone molds are not always necessary.

Dip It

BY ANGUS MACAULAY

Making "dip" molds with Poly Latex False Face Compound is a time-saving alternative to brushed-on latex molds.

How do I make a latex mold without spending days brushing dozens of coats of liquid latex? Dip it.
     Poly Latex False Face Compound has been a standard product for novelty masks, flexible sculpture, and animatronic applications for years. This same formulation is an excellent material for producing dipped latex molds. These are produced by suspending a dry, unsealed plaster model in reservoir of Poly Latex False Face Compound to form a skin. This skin drys to form your mold. That's right, a latex mold made in a single application!
     Start with a bucket of False Face Compound. Dip your plaster model into the latex. Withdraw the model from the latex and correct any bubbles by rotating the model or using a brush. Dip the model back in and let it remain suspended in the latex for 45 to 60 minutes. Remove the model from the latex and stand the model upright. Allow the rubber to dry on the model for 2 to 3 days. A mother mold can be constructed at this point. Remove the mold from the model and allow the latex to dry for an additional 2 to 3 days before doing any casting.
     The process does have some limitations. The model must have a basic pyramidal shape to allow for a seamless mold. The model must be made of unsealed plaster, preferably dry pottery plaster. The total curing time can take several days, but the labor savings is tremendous compared to brushing on layer after layer.

Squash Casting

BY ANGUS MACAULAY

Squash casting is a seldom used but very valuable casting technique. It is a method of producing delicate, thin-walled castings with high-viscosity casting materials. It is particularly useful when casting heavily filled systems such as bonded bronze. There is no need for vacuum or pressure, and the castings are generally bubble-free.
     The liquid casting material is poured into both halves of a two-piece mold. The halves are "squashed" together, forcing any excess material out as the mold closes. The mold halves are then securely clamped or strapped together until the part is demolded.
     Add squash casting to your inventory of casting techniques. It will save the day more often than you might expect.
     More information on squash casting can be found on page 26 of the Polytek® Manual & Catalog.

3. Clamp or strap the mold pieces securely together. This will force out any excess casting material, minimizing seam lines and flashing.

1. Carefully pour the casting material into the mold cavity of each mold half. Try to confine the material to the mold cavity while coating the entire surface.

2. "Squash" the two mold halves together from bottom to top.

4. Remove the near-perfect casting from the mold, leaving behind paper-thin flashing.

Tailor Your Own EFX Rubber with 1-to-1 Mix PlatSil^® Gel-10
New PlatSil^® Gel-10 allows you to formulate your own soft silicone from the basic Shore A-10 hardness rubber.

PlatSil^® Gel-10 is colorless, translucent and rapid curing with surprising tear strength.

• 1:1 Mix by Weight or Volume
• 6-Minute Work Time and 30-Minute Demold
• Retard the Cure with PlatSil^® Retarder
• Soften the Rubber with PolySil^® Softener
• Thicken to a Light Paste with PlatThix
• Color to Any Shade Easily
• Bond the Rubber to Poly Plastics as Flesh to Bones, or…
• Bond Liquid Poly Plastics to PlatSil^® Gel-10 Rubber

Think of the Possibilities!

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