Aldax Moulds and Mouldmaking Supplies

How To Cast Plaster Into Latex Plaster Moulds

Rinse the mould out with Craft Rinse to lower the surface tension and shake dry before securing ready for casting.

Using a strong corrugated carton cut out an opening, using a serrated bread knife or jig saw to secure the latex plaster moulds in an upside down position ready for casting. The flange that surrounds the base of all Aldax latex plaster moulds will support the mould during casting. Use a few pins through the base into the cardboard if considered necessary to secure the mould.

To measure the amount of water required, fill all plaster moulds with water and tip into the mixing bowl. Avoid using warm water, use normal cold tap water as it gives you a little extra time before the plaster sets up. Only fill the bowl or bucket half full to allow easy mixing.
Slowly sift the plaster into the water. ALWAYS ADD THE PLASTER TO THE WATER- NEVER WATER TO THE PLASTER. Spread the plaster over the surface of the water until all the available water is filled with plaster and a dry mound of plaster about 2 to 3 cm high can be seen above the water line.
Now leave the mixing container untouched for 2 to 3 minutes while the plaster absorbs the water then stir gently with a flat bladed plastic or wood spatula. Mix slowly to avoid beating air into the mix. You should not need more than 30 seconds to achieve a smooth creamy mix. Over mixing will cause the plaster to set up quicker often before you can pour it into the plaster moulds.

Pour the plaster into the mould until 1/3 full. Give the mould a series of taps and light squeezes to ensure that all the difficult areas such as undercuts , areas of fine detail, faces ,hands etc are filled with the liquid plaster.
Filling the plaster moulds in this way ensures you will have no air bubbles or pinholes on the surface and you will lose no important detail.
Now fill the plaster mould until it reaches the top, giving a final series of taps to level the base and ensure that all air bubbles have risen to the surface.
The plaster will take about 30 to 40 minutes to set up hard and will feel quite hot during this period. To check if the plaster moulds are ready for stripping from the plaster castings run your finger nail across the base. It should feel firm and dry.

When the castings are ready for removal from the plaster moulds, remove the moulds from the carton and wipe the outside of the moulds with warm soapy water or use some dishwashing liquid.
Gently peel the mould from the base and then pull firmly and as rapidly as possible to release the casting from the mould. It should strip away quite easily if you pull the way the figure is shaped. If you pull against the figure you could break off an arm or leg etc. So choose the path of least resistance.

Finish the casting off by trimming with a knife and sanding the base level. Any pinholes or other imperfections can be filled in with a paste made up of a mixture of plaster and a little water.
The drying of the plaster casting can be carried out by leaving in sunny position for several days or as we do, use either a fan radiator or oil heater to hasten the drying, usually a day. Do not heat too rapidly or you will damage the casting.
The article is now ready for decorating.

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