USG HYDROCAL Gypsum Cements Sealers and Parting Compounds - Manual

Sealers and Parting Compounds Parting compounds (also called “separators” or “releasers”) are needed to prevent adhesion of plaster or gypsum cement to
patterns or models. They also permit removal of plaster or gypsum cement from the surface of the pattern or model upon which
it “sets up.” Porous model materials require sealing prior to application of the parting compound.
Sealing All porous models, patterns and molds must be sealed before the parting agent is applied. Sealing is particularly essential for
wood patterns to prevent dampness from causing the wood to swell, resulting in release difficulty. Gypsum cement patterns
also require sealing to prevent them from absorbing water from the plaster mix and causing the mix to adhere to the gypsum
cement pattern. Patterns of metal, glass, plastic and other impervious materials normally do not require sealing.
A quick-drying lacquer applied by brush or spray gun is an excellent sealer for wood, plaster and gypsum-cement patterns
and master models. Two coats of lacquer provide more resistance to moisture than shellac. Correct procedure is to reduce lac-
quer with lacquer thinner so that the model or pattern readily absorbs the first coat. Apply second coat after first coat has thor-
oughly dried. Where a plaster or gypsum cement pattern is used, apply lacquer immediately after set.
Mahogany patterns or models require special treatment because gypsum cement casts may adhere to undercuts caused by
multiple pores or grain of the wood. A paste wood filler can be used to fill the grain of the wood, but should be reduced to a sat-
isfactory brushing consistency with the recommended thinner. Apply a heavy coat and let it dull down; then wipe off excess by
rubbing across the grain. After wood filler has set overnight, apply a coat of a clear acrylic sealer and allow to dry. Sand the pat-
tern or model and apply several coats of a clear lacquer.
Separators Satisfactory separation agents must provide the following functions:
1. Prevent adhesion to the cast.
2. Protect and lubricate pattern surface.
3. Spread easily and uniformly in a thin, continuous insoluble film.
4. Do not react destructively with the plaster or gypsum cement surface, or with the pattern.
Some of the most common and widely used separators are as follows:
Soaps —A number of special “potter’s” soaps are available for use as parting compounds. “Green soap” (a liquid) is an effective
parting compound when cut 10 to 1 with distilled water. Apply parting soap with a sponge and work into plaster surface. Several
coats may be required on a new mold. Remove excess soap with a clean wet sponge before pouring mold.
Stearic Acid and Kerosene (Stearine) —Formula: 1/4 lb. stearic acid shaved to flakes; 1 pt. kerosene. Melt stearic acid by warm-
ing: remove from heat source and add kerosene with constant stirring until a uniform mixture is obtained. Apply to pattern with
a soft brush, preferably camel’s hair or sable hair. If brush marks show, thin mixture with more kerosene or by warming. This
separator is one of the most widely used of all parting compounds and is particularly recommended for use with glue molds.
Petroleum Jelly (Vaseline) —Formula: 1 part petroleum jelly; 2 parts kerosene. Use petroleum jelly if it is cut back with approxi-
mately two parts kerosene to one of jelly. Blend mixture by carefully heating and thoroughly stirring (Caution—Fire Hazard) .
Apply as a thin coat and brush out thoroughly.
For special purposes, separators other than the above may be advantageous:
Light Lubricating Oil —Use sparingly.
Light Mineral Oil —Particularly effective as a fine fog spray on metal patterns. Must be thinned to be effective.
Olive Oil —May be used if applied carefully while warm. Crisco and other similar hardened vegetable oils used as frying fats are
particularly recommended for use on lacquered wood.
Powered Mica —Has been found useful when finely ground and added to most parting compounds. Satisfactory results have
been obtained by adding 1/4 to 1/2 cup of the powdered mica to 1 qt. of parting compound solution.
E POXICAL ® Mold Sealer Separator —Works well as a release agent of gypsum cements. Thin E POXICAL Mold Sealer Separator as it
comes in the can, using white gasoline or kerosene at a ratio of 1-to-1 by volume. Apply a generous coat to the pattern: allow to
dry 2 to 3 minutes and then wipe off excess with a soft cloth.
H
YDROCAL
®
Brand
Gypsum Cements
Sealers and Parting Compounds
A Gypsum Cement for
Every Industrial Use