What are the forms for plaster and how to work with them?

Gypsum is known as an obedient material, grateful, malleable in processing. Those who work with him know this magic of transforming the mixture into something beautiful, and most importantly, man-made. And forms for plaster of different types and variations increase the creative possibilities of the master working with this material.

Gypsum - an affordable material sold in any building market, is inexpensive, and therefore even if something does not work out when working with it, it will not hit the wallet hard. But so that such mistakes do not happen, you need to be imbued with the technology of working with gypsum and find out what helps turn the powder into elegant decorative items. These are, first of all, forms for plaster casting.

These molds are made from a wide variety of materials, from wood to cement. The plaster casting process is multi-stage. It is casting into molds that lasts a few minutes, but the preparatory procedures and the subsequent ones after the outflow of time and effort take much more. First, you need to make a model of the product, then design and manufacture the mold, then prepare the materials for casting and lubricating the mold. It is important that the counting during casting goes literally for minutes, and when the process has already begun, everything should be at hand, any delay is fraught with failure.

The flask (mold) is lubricated before casting, the solution is mixed and poured into the mold with a very thin stream, allowing the air to escape. After filling, the form should be rotated, shaken a little, so the solution will reach small embossed details. Then the product will be dried in any way you like. After that, the mold is disassembled, and if it cannot move away from the product, it can be tapped with a rubber mallet. The sprue is removed and the part is finalized.

There are many types of forms, and each is attractive in its own way. For example, the glue version is made from gelatin (an alternative could be wood glue). First, glue is made: 7 kg of gelatin are poured with half liters of warm water, this composition is kept for half an hour, waiting for it to swell. A piece of wood glue must be broken into small pieces with a hammer, then soaked in water for 24 hours, changing the water from time to time. At the end of the day, 1.5 liters of hot water are added, and the composition is cooked in a water bath. In this case, the glue pot is closed tightly, at the very end of the process, 300-350 ml of water and a pound of special glycerin are added.

• Silicone. The container is made of a rigid material such as chipboard or fiberglass. The cracks in the container are excluded, all parts of the shell are glued together. Next, you need plasticine for sculptures, evenly lay up to half of the container. The plasticine surface should be smooth. And now the model is pressed into the plasticine, holes are made around with a pencil so that further parts of the form do not move. Then the volume of the material is measured - something free-flowing is poured into the container, and then it is sent to the measuring container. And the surface of the model will need to be lubricated with a release agent.
• Plastic (formoplast). The advantage of such shapes is that the rigidity of the matrix is ​​combined with the thinness of the walls; they also repeat the outlines of the fragments. These forms are not capricious in their care, they are not afraid of exposure to chemical reagents.Plastic molds for casting are made using the technology of hot casting and pressing, this is done on professional equipment. At home, this is almost impossible.
• Rubber. They are made by hot polymerization, strictly under pressure. These forms are made automatically, that is, professional equipment is required. These forms demonstrate high abrasion resistance, they are durable and are able to convey the texture of natural stone virtually perfectly.
• Polyurethane. These molds are distinguished by elasticity, wear resistance, they also do not require any special maintenance, and demonstrate resistance to alkalis. To obtain a polyurethane form, a modified polymer and a hardener are mixed. Polyurethane is considered the most popular type of molds, which is suitable for casting not only from gypsum, but also from concrete and cement.

In the conditions of a home workshop, it is quite possible to cope with the design of the form.

Both the preparatory process and the casting procedure itself are associated with large dust formation. Therefore, in the room where the casting is carried out, ventilation should be established, and then the cleaning of the space. And if there are allergy sufferers in the house, you will have to look for another place to work. It is also worth remembering that a mixture of dust and air, if it reaches a certain concentration, is explosive. Therefore, an open fire in this room is the strictest prohibition.

The main equipment for casting is the mold, but the model of the product precedes it. Here clay or plasticine comes to the rescue, in a word, any material with similar characteristics.

What else do you need to take:

• a container in which water and gypsum will mix;
• a glass with a spout to pour the plaster of Paris itself;
• elastic bands to tighten parts of the form;
• grease brushes;
• drill to drill holes;
• knives and spatulas;
• scotch tape and cardboard.

If you run a little ahead, it is worth telling about plaster. It should be a high-quality composition, no compromises. Unless, if you take building alabaster, then only necessarily sifted through a sieve of 0.2 mm. Alabaster should become, so to speak, downy, without foreign impurities.

It is not a problem to buy a lubricant for the mold, but at home everything is also done quickly and inexpensively: grate baby soap, add water and vegetable oil there. To work on getting the shape, you need either a flat table or a flat floor, as well as smooth plywood or chipboard. The sides of 5 cm will be attached to the bottom of this plywood, and this will form a box for pouring.

It consists of several stages. The first is making a matrix. Without a matrix, it is impossible to achieve that the liquid material cures properly.

Manufacturing features are as follows.

1. Formation of a large relief. For the texture to be large, you need a stone. On the one hand, it should be flat, and on the other, embossed. Both marl and granite will do. You can make a relief surface from sandstone, natural stone, but not only from them. Today you can buy special samples in building markets. And now the selected stone is tried on a board and laid in such a way that two centimeters remain to the plywood wall. And between these fragments in the layout there should be a centimeter gap. The stones need to be outlined with a pencil. A universal glue is applied to the flat part, silicone is also suitable. The places that remain between the irregularities and the surface are filled with acrylic sealant. The remains of it will have to be carefully removed.
2. Shallow relief formation. First, you have to make a box equal to the dimensions of one element with sides of 2 cm. It is convenient to create a small texture from sandstone or buy a ready-made sample, again, in a building market.After composing the unevenness, apply special paraffin to the formed relief. It is melted with a building hair dryer. The molten wax will flow through the gaps, filling the bottom of the small box. When the paraffin has hardened, the sides of the small box will be removed, the model will be removed and placed in the large box. You need to install the resulting model on glue.
3. The following steps are suitable for both silicone and polyurethane molds. The sides of the box must be fixed with self-tapping screws. The joints need sealing. The stones, as well as the inside of the box, must be lubricated with machine oil (you can take melted petroleum jelly instead). This will be the separating composition.
4. Further, according to the instructions on the package, a mixture of silicone or polyurethane is prepared. Stir it until smooth.
5. The box is to be filled with the composition. In the case of polyurethane, the mixture after pouring is warmed up with a construction hairdryer, then excess air bubbles leave the surface.
6. After the time required for the composition to solidify, the box is disassembled. And the form remains.

The following mini-tutorial will help beginners learn how to work with silicone molds.

1. You should prepare the silicone sealant itself, a knife, a sealed container for a matrix for future filling, soap or soapy water, an original object from which the mold will be made.
2. The surface of the original should be prepared - cleaned if there is dirt, putty if the surface is porous. You also need to make sure that the container is tight, which is usually made of something rigid, such as chipboard or fiberglass.
3. To make a one-sided form, the original should be placed in a container, treated with oil or cream and filled with silicone. If a lot of sealant is used, silicone is applied in layers, with a fifteen-minute pause between layers. It is especially important that the top layer comes out evenly.
4. Wait until the silicone is dry, and the drying time is always indicated in the instructions for the sealant. Then the container is disassembled, the workpiece is taken out.

That's it, the silicone mold is ready. If not a one-sided, but a three-dimensional shape is made, then a sculptural plasticine is placed on the bottom of the container, and the original is placed there halfway. The second half of the original is filled with silicone. Then half with silicone is removed, the plasticine is removed, the silicone layer is placed down. A layer of cream or oil is applied to the half where the clay was previously. The second half of the original is filled with sealant. And after hardening, the form is cut with a cantsknife, and the workpiece can be removed without problems.

It is worth talking in more detail about how to use plastic molds. Due to lack of experience, beginners still do not quite understand how plaster grasps, and this process is very fast. When the gypsum expands with significant heat release, the mold happens to "wedge".

What else is important:

• use a separator - if the mold is not lubricated, the plaster will stick;
• when removing the panel from the mold, you need to be very careful - if you overexpose, the panel can also jam tightly;
• it should be pulled out at the time of the start of heating, but this may depend on the type of gypsum;
• to get the panel, you need to walk with a thin blade around the perimeter between it and the form to get a gap into which air will penetrate;
• after the panel has been taken out, it must be placed on the final drying, only on a flat surface;
• washing the mold after casting is considered rule number 1 - rinse it first, and after 20 fillings and wash it thoroughly;
• it is impossible to leave the form dirty overnight, because by the morning everything will stick together so that it will be extremely difficult to tear it off, and it is not clear how to part it;
• if gypsum has already adhered to the mold, only a powerful solution of citric acid diluted with water in such a ratio that the solution is vigorous will help it;
• molds made of plastic, which more than once it was possible to pour gypsum, often wrinkle, therefore they need to be stored freely, you cannot press them with anything heavy.

Casting from plaster allows even at home, in the most modest conditions, to create exclusive interior decorations, to make a larger-scale decor - sculptures and even statues. Plaster makes very nice toys. With the help of silicone construction molds, decorative tiles are made from natural materials, which are actively used in the design of apartments.

You can learn how to make plaster molds from the video below.