acd producing fibrous casts

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PowerPoint presentation

Casting detailed fibrous plasterwork

Unit 315: Producing and fixing detailed fibrous plaster and cement casts

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Assessment criteria5.1 Different types of reverse moulds

5.2 Methods of casting

5.3 Different types of release agent

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Reverse mouldsThis PowerPoint presentation will look at reverse moulds, methods of casting, and release agents used in producing and fixing fibrous plaster and cement casts.

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Plaster reverse cornice mouldA plaster run reverse mould. This is run on the bench and cast to achieve a length of cornice.

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Mould sealed with shellacOnce reverse moulds have been run, they are sealed with shellac and a release agent is applied.

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Reverse moulds can also be made from fibreglass. They are light and easy to store.

Reverse moulds

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Plaster piece mouldsPlaster piece moulds can also be used for casting in plaster or sand and cement. They can be made in several pieces.

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The piece mould will fit together – where the pieces join, grease should be applied to avoid a seam showingin the cast.

Plaster piece moulds

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Plaster piece mouldWhen casting from a plaster piece mould in sand and cement, oil is used as a release agent.

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Plaster piece mouldCement is brushed onto themould to give a good even face, much the same asfirstings when casting inplaster. However, you should not splash the cement.

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Plaster piece mouldThe semi-dry sand and cement mix is then gradually applied and compacted.

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Plaster piece mouldSand and cement is then filled to the top and compacted up to the strike off.

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Plaster piece mouldThe cast is then struck off flat.

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Plaster piece mouldA bar or dowel is thenplaced in the castto allow for fixing.

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Beam case mouldA beam case mould is a run loose piece mould that comprises of two cheeks and a soffit.

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Beam case mouldThe two cheeks are runloose and butted up to thesoffit which is fixed to the bench.

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Beam case mouldBeam case casts areproduced to cover an existing beam – such as an RSJ – or to create a false beam. Casts are struck off with a gauge to an accurate thickness.

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Beam case mouldCasting is carried out as for cornice: two gauge method.

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Beam case mouldTurning a spiral is produced with a turning box. Hinges allow the stock to be lifted clear and the profile cleaned.

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Beam case mouldA drum is made on a tapered spindle. Plaster isapplied to the shellackedand greased spindle.The spindle is turned and as the plaster stiffens, the shape forms.

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Small column produced from turning box/plasterers’ lathe.

Beam case mould

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Beam case mouldOnce a spiral balastrade or small column model has been formed, the next stage is to produce a two-piece mould.

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Beam case mouldA back and front mould orpiece mould is produced with joggles for accurate location of the pieces.

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Beam case mouldA plaster case supportinga layer of pliable rubbermoulding material.

Note: the funnel hole where rubber is poured.

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Beam case mouldDeeply contoured models may be covered with a controlled thickness ofrubber – either silicone or PVC.

This method avoids largepockets of moulding material.

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Beam case mouldLips and joogles can beformed to lock the moulding material into the case.

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Flood mouldFlood mould is made bypouring moulding materialover an open model ringedby a retaining wall.

Material is poured coveringthe highest point to form a flat back to the material.

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Flood mouldA low-relief ceiling centre is an example of a mouldproduced in the flood mouldmethod.

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Flood mouldFlood moulds can be used for panels and small sections of moulding.

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Run case reverse mouldA run case reverse mouldproduced from a run core.

The core is formed over the model by covering the model in wet newspaper and running a profile. This is run off to core thickness.

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Run case reverse mouldOnce the mould is poured, the case is taken off andshellacked. French chalk is applied to act as a release agent for the rubber.

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Run case reverse mouldRubber is trimmed and the pour holes are cut to allow for the rubber tosit correctly in the case.

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Any questions?