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Mold Making - Two part plaster

Updated: Feb 20, 2018

A simple two part mould of a tube using plaster as the mold material.

Materials: Clay and plaster (and water), petroleum jelly and the item to be molded. Tools: Knife, rolling pin, small board, cheese wire, clay tools, rolling pin, roller guides (not essential), gloves if you have delicate hands.

Clean Vaseline off mold with Methylated Spirits. Coat with solution of French Polish and meths for the first coat, then build coats of French Polish.

Best for fibreglass (GRP) molding.

Tried with plaster and no release agent and it was very diffucult to separate without damaging both mould and cast.

NB, dilute French/Meths mix more for greater penatration, use a mould release on both halves before pouring.

Will try this method again for a clay slip cast (no button polish). For casting plaster in plaster a flexible inner mould would ease removal.

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