Casting simple moulds with plaster of Paris.

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This is a short introduction from The Magic Garden for beginers on plaster history and crafting with plaster and rubber latex moulds/molds.

Plaster of paris derives its name from a large gypsum deposit in montemartre in Paris, France where it was widely used for building construction, decorative ceilings and cornices, sculpting, making molds and casting just to name a few. Plaster of paris has been used from primitive times to the present and is a fine white gypsum powder that will form a paste when water is added and will harden into a solid mass when set. Strength can vary according to the water plaster ratio and although solid when set it is still rather soft and can still be manipulated or cleaned with sandpaper or a wet sponge. As with all types of plaster read all instructions first and use only in a well ventilated space, outdoors is the best I find.


Pouring your plaster!

Have all ingredients, moulds, supply of water, mixing container, spoon ect all ready to go before you begin. Try and use a table outdoors in the shade with newspaper over it for easy clean up.

If your mould sits flat on the table surface you are ready to mix your plaster if not then you can use a number of methods to support the shape of the mould when pouring.

Some of these methods are either a box or bag of dry sand  sawdust rice or peanut shells and press the mould into the support (sand) quite firmly in every part of the mould ensuring it is even all over and the mould has kept its shape. Remove the mould and wash if needed, if you are pouring 1 mould fill it with water and then tip that water into a bowl (this is how much water you need for that mould).

You can also use an icecream container filled with water (only fill it as much as you need to sit the moulds in) and place the moulds on top of the water and weight them down with coins ect and then freeze the container. When frozen remove coins and pour straight into the moulds, by the time the plaster has set the ice will have melted slightly easily releasing the mould and cast. Refreeze for your next use.

Always add your plaster to your water mixing thoroughly with a spoon until your mixture resembles a thin cake batter with no lumps. Some moulds will require a stronger plaster mixture for delicate casts to come out in one piece, this is achieved by adding more plaster than normal so the mixture is thicker and so it will set stronger. Alternatively you can mix craft glue with your plaster mixture to give it extra strength.

Plasterers/concreters/cementers take note of the following as you will be amazed at the difference in air bubbles when you pour using a wet mould.

Before pouring wet your mould with clean water, tip out the water and shake off the excess but leave the mould wet and place it gently into the support you have already made for the mould.

Pour in your plaster mixture halfway and where possible gently tap the mould to ensure the plaster has gone into every nook and cranny and also to release any other trapped air bubbles (the wet mould will also collect and push most if not all of the air bubbles to the top and sides) finish pouring to the top of the mould and let it set for 10 to 20 minutes depending on the size of the mould.

All moulds are different and practice with your mixture, levelling and filling of some moulds may be required- Be patient.

When taking casts out of moulds remember each mould is different. Some will need to be gently pulled away from the plaster edges, some will need to be gently peeled off the cast, some will need to be rolled off the cast and for some moulds you will need a combination of the above.

Never tip your old plaster water down the sink it will clog it up over time, tip it on the garden instead the plants will love it.

Let your cast dry for about a week depending on temperature in a warm dry place before painting. The cast will feel quite heavy when first taken out of the mould but when dry it will be half the weight it was.

Cant wait to paint your wet casts?

If you are in a hurry to paint your casts and dont want to wait for them to dry naturally they can be placed in the microwave oven on defrost on a very low temperature for 8 to 15 mins depending on the size of the cast. It will be very hot when it comes out of the microwave don't burn yourself and let it cool down naturally. If the piece was larger or still does not feel dry then repeat the process then paint away.

Caring for your moulds!

After every pour rinse your mould in water inside and out making sure there is no build up of old plaster which will affect the performance and life of the mould.

Keep moulds out of direct sunlight as they will deteriorate very quickly if left in the sun. When pouring do it in the shade.

When moulds are not in use wash then dry and dust with talculm powder and store in a sealed plastic bag in a dark place.

With proper care and use your Magic Garden moulds will last for years and give you endless hours of enjoyment, fun and creativity.


Warm Regards

The Magic Garden

Practice and you will succeed!

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