![]() Mahogany patterns or models require special treatment because gypsum cement plaster casts may adhere to undercuts caused by multiple pores or grain of the wood. Apply second coat after first coat has thoroughly dried.Where a plaster or gypsum cement pattern is used, apply lacquer immediately after set. Correct procedure is to reduce lacquer with lacquer thinner so that the model or pattern readily absorbs the first coat. Two coats of lacquer provide more resistance to moisture than shellac. A quick-drying lacquer applied by brush or spray gun is an excellent sealer for wood, plaster and gypsum-cement patterns and master models. Patterns of metal, glass, plastic and other impervious materials normally do not require sealing. Gypsum cement plaster 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. Sealing is particularly essential for wood patterns to prevent dampness from causing the wood to swell, resulting in release difficulty. Hydroperm Gypsum Plaster Sealing All porous models, patterns and molds must be sealed before the parting agent is applied. 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. 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. For producing permeable plaster molds for precision casting of many nonferrous metals and alloys. HYDROPERM gypsum plaster is a specially formulated product incorporating an air entraining agent to provide permeability.
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