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Casting Product Index - Accessories Index

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CASTING WINTERSTONE
Lay-up & Reinforcing Techniques

TECHNICAL BULLETIN
(Updated July. 2000)

The configuration, size and type of sculpture will generally dictate the type of mold to be used and the casting process employed. For example, a life-size bust sculpture 18” to 24”, would in most cases require a multi-piece mold and be “slush-cast” hollow. This would require an initial coating of “face” mixture prepared using the recommended water content, metallic and/or pigment powders if desired, into the assembled multi-piece mold.The initial coating should be sufficient to coat the interior mold surface up to a thickness of approximately 1/16”. This must be immediately coated with a back-up mixture which incorporates 1/4” ARG(alkali resistant fiberglas strand). Repeat the process until a minimum thickness of at least 1/4” is achieved. If the mold configuration allows hand access, the back-up thickness can be achieved applying by hand a mixture consisting of Casting 2000 and Sculpting Mix reinforcing with overlapping strips of ARG mesh. Once the reinforced shell has completely dried it can be patinated and sealed. Demolding may be done in 24 hours; air-drying of at least 48 hours should be allowed before proceeding with any surface patina-ting or finishing. If the sculpture is to be placed outdoors it is recommended to wait approximately 30 days before doing so.

If the mold is cast solid this only adds weight and not necessarily strength to the casting. For outdoor pieces, the less mass there is the less thermal stress occurs between temperature affected surfaces and the relatively non-affected interior. The incorporation of ARG fibres and/or reinforcing mesh is sufficient for most, if not all, interior or exterior conditions.

When casting large or monumental sculptures requiring multi-piece molds,or bas-reliefs , the lay-up technique may be employed. Each piece of the mold is laid-up or built-up with the required mixture and thickness individually, after which the sections are assembled together. Each section requires a 1/16” thin layer of “face” mix using Casting 2000 (with or without metallic and/or dry pigment powders) brushed or stippled onto and into any detailed mold surface. A back-up mixture should follow immediately including 1/4” ARG strand. A back-up mixture consisting of 1 part Casting 2000 : 1 part Sculpting Mix and 15 - 17 % water, will not only provide a good pot-life and working consistency but will also be suitable for most situations. The back-up mixture may be kneaded-in by fingers (similar to clay modeling) or trowelled-in. This back-up mixture may be varied up to 1 part Casting Mix : 4 parts Sculpting Mix depending on the size of the sculpture, pot-life, and setting times desired for the specific application. In stress point areas additional reinforcement is achieved using ARG mesh or galvanized wire mesh which are laid into the mixture to enhance the structural strengths of the shell where required.

Prior to assembling the individual sections of the mold together, a “bead” of face mix should be applied along the adjoining edges of each piece. Once the mold pieces are tightened together this will produce a relatively sound joint (see figure A). On larger pieces, particularly if they are to be founded outdoors and subjected to severe climatic and/or exterior applied stresses, it is recommended that the joint be additionally reinforced on the inside if hand access is possible (see figure B). If hand access is not possible reinforce on the outside (see figure C). Once the outside joint has cured and hardened it may be sanded down and burnished to match the adjacent surface. If two cast pieces are to be joined, ie. an outstretched arm to a torso, refer to the procedure outlined in (figure D).

The style of mold and mold material to be used depends on the type, size, shape and intricacy of the sculpture to be cast. Appropriate release agents may be required depending on the choice of mold material. Please refer to technical literature provided by various mold material suppliers.