Moulding Techniques

There are lots of different ways to make moulds from models. Flood moulds/open mould/solid mould can be used on PVC and cold pour. Flood moulds do not need a lot of preparation, a basic wood or clay frame is all that is needed. There are a few disadvantages when using flood moulds such as lots of moulding compound is needed because it has to be higher than the model. The model being used can be from anywhere such as a house or a stock item in a workshop so it needs to be remade. To make this kind of mould, the model should be placed on a flat surface that can be sealed. A frame needs to be made to go around the model. There should be at least a 25mm gap between the frame and the model. Shellac is used to seal the frame and then it is fixed to the surface that the model is placed on. All the junctions should be sealed with plaster and the frame must be sealed well so that no liquid can leak through. The moulding compound should be poured and there should be 13mm more depth that the highest point on the model. Do not pour the compound directly on to the model because it cools down quickly and leaves smears and marks. For the compound to be able to stand level, you should use plaster reinforcement to go over the back of the compound, then strike off so that it is level with the frame. Case mould/clay case mould/closed mould uses a fibrous plaster case that holds the moulding compound to create a reverse mould. A case moulding reduces the amount of moulding compound you need to use. The case mould also helps the compound to cover the entire model evenly. To make the case mould, the model needs to be placed on to a moulding ground. Then you will need to hit the boards of clay until they are the thickness that you need for cold pour. The model should be covered with damp newspapers and then the clay boards can be laid over the top, making sure all joints are sealed. Using clay strips, make a sort of lip that are narrower at the top, around the outside of the model to hold in the moulding compound in place once the case has been formed. All of the lay needs to be smoothed out and enough strips of canvas should be cut to have two layers placed over the clay. Timber and rope then need to be cut, the rope needs to go around the clay and the timber should be on top of the rope. A case should be cast over the clay with firstings and seconds. Mark out the case with a pencil on the moulding ground so that you know where to place it back when needed, and then remove the case, all paper and the clay. The clay should then be wetted down and covered to stop it drying out. To prepare the case for pouring, old canvas is used to clean off all the old clay. Air hole are cut into the case at low spots and pour holes are cut into the case also. The more air holes that are cut in the better, but you do not need a lot of pour holes. The more pour holes you have, the more compound you will need to use. The case can then be placed onto the pencil marks you made earlier. Clip wads can be used to hold the case in place. Use clay and plaster to fix the pouring funnels into place, making sure the funnel is kept off the back of the case. The air holes will need to be blocked off when the moulding compound comes through so some clay balls need to be made to block the holes, then double check that all of the joints are properly sealed. Once this is done, you can carefully pour the compound in Only remove the funnels, clay balls and wads once the compound has set completely. Remove the case and take out the compound, cutting off the compound in line with the air holes. Shellac and grease are used in the plaster case so that the moulding compound can be put back in. Skin moulds are used when there is not a lot of moulding compound available and you have limited time. They are made the same as the flood moulds The only difference is that less moulding compound is poured on to the moulding ground. The compound is then moved from the moulding ground with a small tool and is gently poured over the model. This should keep being done until the model is covered with a thick skin. The compound can then be covered with a plaster case. There will be a few variations with each method. For example, the time you have to create the mould, the equipment and materials you have to be able to make the mould.