Plaster of Paris is a versatile material for three-dimensional work. Plaster of Paris is available in two basic forms, as a white powder sold typically in 1, 10 and 25 kilo bags, or as a form of plaster impregnated bandage/scrim, sold in cut sheets, small rolls and multi-roll packs. Plaster of Paris hardens through a chemical reaction initiated through contact with cold water or even dampness in the air. In powder form, Plaster should always be mixed by adding the powder to cold water, never water onto powder. Plaster impregnated scrim pieces (Mod-Roc) are placed in cold water for seconds to absorb water, before being placed and formed over the armature and the surfaced smoothed, usually by hand.
Cold water is used to ensure sufficient working times. The use of warm or hot water will accelerate the chemical hardening process, which may prove hazardous if the materials harden too rapidly while pupils are still handling the plaster slurry or sheets. On contact with water, this material hardens and then slowly becomes hot. Temperatures as high as 60 degrees centigrade can be reached. Skin damage can result at much lower temperatures, perhaps as low as 45 degrees centigrade, if contact is prolonged.
Making a cast enclosing any part of the body using this material is potentially very dangerous, particularly if the thickness of the cast exceeds a few millimetres. As a rule of thumb, if a decision to make a cast is made despite this clear warning, use no more than two layers of scrim impregnated with plaster, e.g. ModRoc.
Hands, fingers, parts of the body should never be submerged into liquid mixed plaster of Paris and held there until the plaster hardens.
Failure to follow this guidance can cause severe burns that may require surgical removal of affected tissue or amputation of digits or a limb.
Direct, prolonged or repeated contact with the skin may cause irritation and attempts at removal can result in abrasions. Rinse with water until free of material to avoid abrasions, then wash skin thoroughly with mild soap and water.
If Plaster of Paris is in contact with eyes, first rinse with plenty of water for several minutes (remove contact lenses if easily possible), then take to a doctor.
Plaster of Paris dust needs to be controlled as it is an irritant that can cause breathing difficulties that are usually mild.
Storage of Plaster of Paris and Plaster impregnated bandage/scrim should be in sealed containers to prevent any moisture or even damp air initiating a chemical reaction, rendering the materials unusable. Plaster of Paris powder should be handled using a scoop and when adding to cold water, limit shaking and the raising of dust into the air. Open bags of plaster must be kept sealed.
To download guidelines on the use of Plaster of Paris in art & design, click here.
HSE case study on the misuse of Plaster of Paris on a 16 year old art student, can be viewed here.
CLEAPSS guidance - MRAT - 152 - Plaster of Paris
CLEAPSS guidance resource - PS072 - Using plaster of Paris in schools