Rubber Latex Mold Instructions

Rubber Latex Mold Instructions

1. The model should be perfectly clean and, if made of plaster, Permoplast, other oil modeling clays, or any porous material, it must be coated with plaster separator to prevent the latex from sticking to the model. Glass or pottery models need no coating of any kind.

2. Place the model on a flat, smooth, non-porous surface such as glass, metal or marble.

3. Models are often slightly uneven around the base. To prevent the latex from running underneath the model, seal all uneven spaces with modeling clay until the base is perfectly smooth and flush with the working surface.

1. Apply a thin coat of latex over the entire model and extend the latex out from 3/4" to 2" from the base (depending on the size of the model) to form a margin around the model. Be sure that the latex reaches the deepest crevices and that there are no air bubbles. Blow bubbles out as you work, or brush them out. The most common method of applying latex is with a brush, but it may be applied by dipping or spraying (latex may be diluted with one part water to ten parts latex).

2. When the first coat of latex is dry, apply the second. Continue with from 6 to 12 applications of latex (depending on the size and shape of the model) and allow intervals between each coat for drying. It is impossible to speed up the process of making rubber molds, since time for proper drying is required between all steps to obtain the best results. Since the liquid latex tends to pool in the crevices, brush the excess off with a brush leaving an even, thin coat all over.

3. When toughness of a mold is required, and flexibility or elasticity is not so necessary, a mold may be reinforced with gauze strips 1" or 1 1/2" wide which can be embedded in the next application of liquid latex. Place the strips over parts in high relief and deep crevices where there might be a strain on the mold. (The use of gauze strips in a rubber mold is optional).

1. Leave the model in the mold and: a) dry at room temperature for a period of 3 days or b) for quick drying, heat overnight at 110°F. NOTE: When using Permoplast or other oil based modeling clays, use process (a) only.

2. After drying (either process [a] or [b]), heat the rubber mold at 110°F for 48 hours. This completes the curing and prevents distortion in use.

3. Test the mold by pressing the sharp point of a pencil or tool into the mold to see if it snaps back. If no impression is left, this is an indication of a good, fully cured mold.

Now, before the model is ever removed from the mold, it should be decided if a Plaster of Paris shell or backing is needed to prevent distortion when pouring the casting material. For some molds, it is possible to make a plaster backing in one piece. For others of more complicated design with undercuts, it is necessary to make a plaster backing in two or more pieces in order to be able to remove the latex mold easily.

1. Brush the mold (model is left inside) with plaster separator.

2. To make a simple one piece plaster backing, build up a wall of clay or wood reinforced with clay at least 1 1/2" higher than the mold, then pour in the thick Plaster of Paris mixture. As soon as the plaster has hardened, the framework may be removed and the plaster mold turned over to lift out the latex mold.

1. The rubber latex mold is fitted into the plaster backing (if one has been made) and the liquid casting material is poured into the mold until full.

2. As soon as the casting material hardens, the cast piece may be removed from the latex mold.

For additional reproductions, this process is repeated immediately.

1. Keep latex jar tightly closed when not in use.

2. Before using, remove any film that has hardened on the top surface, then stir the latex.

3. Store at moderate temperature.

4. Keep brush in soapy water solution.