Plastercraft FAQs

 

Q: What is Plaster of Paris?
A: Plaster of Paris, or simply plaster, is a type of building material based on calcium sulphate hemi-hydrate (gypsum), nominally CaSO4 ½ H2O). It is created by heating gypsum to about 150º C. Heating also takes place when re-mixed with water (casting), hardening to a smooth solid which does not shrink or lose volume, because it hardens before all the water can evaporate. It is a common building material as well as a versatile medium in sculpture.

Q: What is a casting?
A: A work which has been produced by molding. Creating the positive.

Q: What does exothermic mean?
A: Heat set up during the cure of a plaster casting.

Q: What is fibre glass?
A: Very slender fibres made from glass.

Q: What is a Release Agent?
A: Material applied to surfaces to aid parting.

Q: What is Patina?
A: The finished colour of the surface of a casting.

Q: What is scrim?
A: A course woven fabric, usually made from jute used to re-enforce plaster of Paris castings.

Q: How do I get rid of air bubbles in a casting?
A: Vibrating a mould during the setting process encourages air to escape.

Q: What is an armature?
A: An internal support.

Q: What is the best way to mix plaster of Paris?
A: Always add the plaster to the water.

Q: How do I remove mildew from my castings?
A: Fully dry your plaster casting and wash spots off with a dilute solution of bleach.

Q: My plaster mix sets before I pour it into the mould?
A: You can delay the setting time of the mixture by adding sodium citrate or citric acid to the water prior to adding the plaster powder.

Q: How do I speed up the setting time of my plaster casting mix?
A: Add potassium sulphate to the water prior to adding plaster.

Q: The ears & nose of my model dogs are always imperfect and have bubbles which ruin my plaster craft – how do I eliminate these?
A: Use a very soft (sable like) long haired paint brush and stipple/agitate it within the plaster filled mould in the areas of nose and ears – this should dislodge bubbles.

Q: I am trying to make some hill and rock scenery for my model railway – how do I create a mountain without it collapsing every time I apply plaster?
A: Construct an armature of wire and cover it with wire mesh (chicken wire) – then cover the mesh with strips of plaster bandage – allow to dry and paint.

Q: I am making plaques and hanging plates – what is the best way to attach a hanging hook?
A: Just before the plaster hardens in the mould push a piece of wire bent like Ω into the plaster and allow 2 set – copper, galvanised or plastic garden wire are best.

Q: I keep breaking my models when taking the latex mould off – how do I stop this?
A: Allow a little longer for the plaster to set and lubricate the outside of the mould with liquid soap so the mould will slide back over itself like a rubber glove.

Q: How do I make the paint stick to the surface of my plaster models?
A: Allow to thoroughly dry first – if still a problem seal the surface of your plaster casting with a sealer like shellac or gesso.

Q: I want to make my own moulds – what materials are available?
A: Latex rubber, two part silicone rubber and alginate are all used a great deal.

Q: I want to try body casting or life casting but I don’t want the plaster bandage to stick to my skin – how do I stop this?
A: An application of baby oil, Vaseline or KY jelly will usually prevent this – better still apply safe dental alginate over the skin after the oil, allow to set and then apply the plaster bandage

Q: Can I cast a very young baby's hand or foot?
A: Yes – the baby casting kit includes all safe materials and all details will be reproduced

Q: Can I keep my rings and jewellery on when moulding?
A: Yes – and when you use our moulding material these will be reproduced in very fine detail and add character to your plaster cast.

Q: Is pregnant belly casting easy and safe to do?
A: Yes the process is extremely safe for baby and easy to carry out, using our belly casting kit, the whole process should only take 40 minutes

Q: Can I take a mould of my pet's paw?
A: Yes – this process is ideal when using our pet print kit and our materials don’t stick to the paw, skin or fur