Mix plaster - instructions + mixing ratio
- The different types of gypsum
- Stir the plaster
- Process plaster
Gypsum is not the same as gypsum. Who wants to tinker with it, should first think carefully what he wants to do with it, what should be achieved and what type of plaster is best suited for it. They all have to be touched, but there are differences.
Gypsum is a mineral and occurs in nature. However, it can also be produced artificially. Gypsum for crafting and modeling must be burned before being sold by the trade so that part of the water contained in it is extracted.
With gypsum there are different sorts, which simply at the different occurrences (where it is dismantled) and the grain lies. Thus, the properties may well differ. This is particularly noticeable when applying the gypsum compound, ie when mixing.
If the mixing ratios of the individual types of plaster are set the same, different consistencies often result. The flow behavior is affected as well. It is favorable if the mixing ratio is indicated on the package. Otherwise, you can just experiment a little bit to determine the right gypsum-water ratio.
The reference value for the correct mixing ratio is: 1 part water to 1.5 parts gypsum
Tip: Never put the water in the plaster, but always the plaster in the water !!!
The different types of gypsum
As mentioned, one finds gypsum deposits in nature. In quarries the gypsum is mined. Then the rock is fired and ground. The decisive factor for the different types of gypsum is the height of the firing temperature. The process removes water from the gypsum. This must then be fed back when stirring.
One differentiates mainly between gypsum as building material or model and form plaster.
- Model plaster (modeling plaster) - usually called alabaster plaster. The plaster for all artistic and handicraft work. He is pure white and very finely ground. Because it hardens very hard, this plaster can be well worked with tools. It is used for the construction of plaster molds and casting of plaster relief, in modeling for landscapes and diorama construction. For crafts the most used and best plaster.
- Hard plaster - used especially by dentists for dental impressions, is also ideal for crafting when creating objects with thin and precise surfaces. This plaster is obtained in the laboratory for dental technicians. There are different degrees of hardness. Most of the smallest is enough for crafting.
- Stucco plaster - clearly yellowish or gray and less finely ground than model plaster, takes longer to set and is softer and more porous, which makes it less easy to work with tools. Used to make ornaments on walls and ceilings
- Gypsum plaster - this gypsum stiffens very slowly and adheres very well to plasterboard, which is why it is mainly used for applying gypsum plasterboard as a wall dry plaster.
- Joint plaster - contains special additives that improve the water retention capacity of the plaster. The plaster stiffened very slowly. This is especially important when connecting plasterboard.
- Plaster of plaster - coarse plaster, which is used for the production of plaster and mortar during construction. Also used for rough stucco work.
Tip: As a rule, you can get along well with the inexpensive plaster from the hardware store. If you buy in specialist shops, eg in craft supplies or in the model shop, you pay considerably more.
Before starting to mix gypsum, prepare all the ingredients. All hand tools and utensils should be very clean so that no impurities enter the gypsum, which then appear after drying. Needed:
- It is best to use round vessels for mixing. Are suitable, depending on the desired amount of bowls, buckets, bowls, cups, etc.
- Plastic containers are the easiest to clean. Plaster cups made of black soft rubber are often used by professionals. They are handy, inexpensive and easy to clean from hard gypsum residues. You just have to squeeze them and the hardened plaster will burst.
- For stirring, rubber spoons, wooden sticks or spatulas are used.
- Weighing balance
Stir the plaster
It is important to adhere to the specifications on the packs as far as the mixing ratio is concerned. The individual ingredients, ie gypsum and water, must be weighed exactly. Professionals do that mostly for feeling, but for beginners or crafts enthusiasts who rarely work with plaster, it is worth measuring.
1. Measure gypsum and water accurately. Both should be at about the same temperature, so do not use too hot or too cold water.
2. Add water to the mixing vessel. This should be big enough. The gypsum compound needs a lot of volume. Too small vessels like to overflow. In addition, it is difficult to stir.
3. Grease the plaster powder loosely and not all at once into the water. Do not fill in too quickly, otherwise air can be incorporated. It comes to so-called plaster tubers. When larger amounts of water sprinkle quite quickly, otherwise the already sunken gypsum sets, while the top is still strewn. First add all gypsum powder until you start to stir. The right amount of gypsum is reached when a kind of crust forms on the surface and the interspersed plaster does not sink any more.
4. Stir all gypsum powder until a smooth mass is obtained. If lumps are formed, they are best crushed on the edge of the vessel. It is important not to touch the air. Therefore
5. Frequently shake the vessel or take it up and put it on harder, so that the trapped air bubbles can escape. They usually rise to the surface and can be crushed there.
6. Let the mass rest for 20 to 30 seconds - sump.
7. Continue stirring! You can do this manually or work with a machine. Manual editing takes longer. 2 to 3 revolutions per second are ideal. Is stirred for about 30 seconds. For slow-setting types of plaster usually has to be stirred longer.
Plaster cures quickly. Within 5 to 10 minutes it becomes steadily firmer. Depending on what you want to work, you have to go fast, because it continues to pull quickly and is usually after 15 minutes no longer work. He should then no longer be disturbed, so no longer touched, otherwise he will be friable.
If you want to work on the plaster, you should allow it to harden for at least 2 days, but better for longer. It has to dry out completely, becoming lighter and lighter. Who wants to perform fine detail work, it should begin immediately after the end of the mixing process.
Beginners should always start with simple and smaller projects to get a feel for the mass and its behavior in thickening and hardening. Over time, you have a feeling of how the plaster reacts and how fast you have to work. Often, air bubbles are a problem. Especially with pictures and small figures that does not look nice. Therefore, while stirring, make sure that not so much air penetrates and the bubbles knock out or knock out. If you need firmer gypsum you have to work with less water. For the production of fiber plaster cotton fibers, but also hemp or animal hair can be added. This also makes the gypsum compound firmer.