The use of gypsum in construction and everyday life has such deep roots that it can easily be attributed to the most ancient building materials. But this does not make it easier to work with him - you need to know not only how to dilute gypsum, and what proportions to use, but also many other subtleties associated with this material!
Building gypsum - sets quickly, lasts a long time!
AT repair work gypsum is used very widely: both as part of other solutions as an astringent component, and "solo". Gypsum you will meet in plaster mixtures, modern modeling and sculptures are made of gypsum, as well as. Building gypsum is a white powder with a grayish tint that intensifies when water is added. This material is obtained from gypsum stone, which is fired in kilns at a temperature of about 150 ° C and crushed to a homogeneous powder.
Depending on the grinding, you can find fine, medium and coarse gypsum - only fine grinding is suitable for construction and repair purposes! Powder, which is used in construction, is divided into three temporary groups:
- group "A" indicates the highest setting speed - from 2 to 15 minutes;
- group "B" - these are materials that set no faster than 6 minutes and no later than half an hour;
- group "B" - this group includes gypsum, which hardens no earlier than 20 minutes.
Gypsum is divided into grades according to its degree of compression. For example, material labeled G-6. It is easy to guess what the letter means, but the number tells us what the compressive strength of this material is, in this case, 6 MPa. As a reminder of the school curriculum, 1 MPa (megapascal) is the pressure exerted by 10 kg per square centimeter.
For construction works they use material from G-2 to G-7, which belong to group B. By the way, alabaster is a generalized name that covers all building brands, and in professional terminology this term has long been abandoned, preferring to specify information using marking. A notable feature of building gypsum is its ability to expand when it hardens. while other materials shrink. The expansion is insignificant - the volume increases by 1%, which fits well with the needs of builders and repairmen.
What else gypsum is good for is its sufficiently high strength at a low density of 1200-1500 kg / m 3. Speaking in plain language, this material will be 2 times lighter than the same cement! In addition, it has low thermal conductivity. These are all pros, but there are also cons! The most important is too fast speed solidification. Therefore, in work it cannot be stored in this state for a long time, or rather, with all your desire, you will not succeed, since the gypsum will harden in the container.
Constant stirring will not save, moreover, this cannot be done, since gypsum will lose its characteristics every minute.
That is why gypsum is kneaded with "factories", as the craftsmen call small portions of mixtures. The master has only a few minutes to use the “winding”, during which he must not only apply it to the surface, but also level it. If this is not done, and the material hardens at least partially, it is no longer suitable for serious work! This is also called "dead" gypsum, after drying it will crack and crumble, spoiling all your work.
Since gypsum powder has a low hygroscopicity, its use is rational only in rooms with high humidity. If you are afraid for the condition of the coating, it is better to additionally cover it with a moisture-proof compound after it has completely dried. Since the structure of the material is quite porous, the surface will first need to be prepared - apply an appropriate primer.
Storage conditions - what is the shelf life of gypsum?
Stocking up on plaster is an extremely bad idea! Firstly, this material cannot be called scarce, and secondly, no matter how hard you try to provide it with proper storage conditions, treacherous moisture will still find a crack through which it will penetrate into a bag or other container with gypsum and merge with it into strong alliance. Even in a perfectly dry room, it will lose its qualities over time. The same applies to derivative materials - if you are going, try not to postpone work after buying the materials.
But even if you purchased bags of gypsum in order to use it in the coming days, you need to pay special attention to the storage conditions of the powder. The most important and obvious condition is dryness! It is best to place the material bags 30-50 cm above ground level, for example, on pallets or on bags of other material.. If holes have formed in the bags during transportation, then it is better to close them with pieces of polyethylene.
If for some reason you doubt the quality of the powder, perform simple tests before using it. All you need to do is stir a small amount of material and apply it to metal surface. Try to accurately record the time from the moment of stirring to the start of hardening - these indicators must correspond to the brand declared on the package.
How to breed building gypsum - simple calculations
Whatever brand you choose for work, building gypsum should be diluted in the opposite way - not water is added to the powder, but powder to water! Before starting work, choose a suitable container, plastic or metal, to create a solution, the main thing is that later it would be convenient to scrape off the remnants of the material from its inner walls.
Pour water into a container - one part to two parts of the powder. Then slowly, trying to distribute the powder over the entire water area, stir the mixture until the water is completely absorbed into the powder. At least a little the resulting solution should stand - if the material is slightly warmed up and thickened, it's time to use it! It is very important to remember that none of the components can be added separately to the solution that has already begun to set! By doing this, you will ruin the entire mixture, resulting in a solution with extremely low astringent characteristics.
How to dilute gypsum - the proportions of different compositions
The disadvantage of a mixture of gypsum powder and water is a very high setting rate. It is necessary for the master to gape, or to make too much batch, and write wasted! That is why ways have been devised to slow down the rate of solidification of this material without losing the rest of its characteristics. The first method is the preparation of gypsum adhesive mastic. For this composition, 15 g of glue is diluted in a bucket of water. Instead of wood glue, you can use another, more complex solution of lime and hide glue.
First you will need to prepare a lime-glue mixture. To do this, take 1 kg of skin glue, soak it in five liters of water and leave it for 15 hours - during this time it will get wet and acquire the desired consistency. 2 kg of lime dough is added to this mass, it is well stirred and boiled over low heat for 5 hours. As a result, you will receive a ready-made concentrate, which can be completely or partially diluted in water (for the whole mass - 20 liters of water) and mixed with gypsum.
For one liter of lime-adhesive solution mixed with water, 8 kg of gypsum must be added. Also calculate how much water may be needed for this mass - as you already know, it is better to add powder to water, and not vice versa, therefore it is recommended adhesive composition stir with the liquid immediately in the calculation and on the gypsum. Such a mastic begins to set no earlier than 20 minutes after its preparation, which gives enough time for "manoeuvres". By the way, adding ordinary table salt will allow you to get the opposite effect, namely, to speed up hardening!
This material is very plastic, applied to almost all types of surfaces, hardens quickly and is easy to process. It is used in various sectors of the economy: as a fertilizer, components of pulp and paper production, ingredients in the production of paints and enamels. And, of course, the burnt powder is used for castings. internal elements building decor, as a binder in construction.
Exist special types building brands. High-strength mixtures and gypsum-cement (pozzolanic) binders are produced. Working with plaster is not very difficult. Hardening, it forms a stone-like mass that is very convenient for processing. Therefore, it is very widely used for the production of various crafts. Here its clear advantage is the high fluidity of the solution, which is very convenient for casting products.
The finely porous structure makes gypsum an indispensable material for creating all kinds of injection molds, also with the addition of high-temperature components.
The disadvantages include its low strength and hygroscopicity, so the use of such materials in rooms with high humidity is undesirable. If necessary, waterproof coatings should be applied. In this case, you need to consider how to work with gypsum correctly. The porous structure contributes to the absorption of the coating applied directly to the surface. Therefore, it is necessary to carry out a preliminary primer of such a surface under an appropriate coating.
How to dilute gypsum - a few preliminary notes
It should also be noted the time of work with the solution. Here, in many respects, the role in which proportions to dilute gypsum plays a role. But, in general, its hardening time is from 20 minutes to an hour. Reuse of gypsum that has already begun to harden is undesirable, because. this affects the quality of work for the worse. This circumstance must be taken into account before using plaster. A solution with its content should be prepared only for the amount of work that can be completed in a specified period of time.
As practice shows, he has not yet been able to find a full-fledged replacement, so you need to know how to properly dilute gypsum. It will always come in handy for doing minor repairs, putty works, etc. When preparing a plaster test, proportions must be taken into account. At more powder, the dough is thicker, the material hardens a little faster. And vice versa. We can say that for a thicker solution, the ratio of gypsum and water will be about 2: 1, respectively.
The average density (let's call it normal) will be obtained if about one and a half kilograms of the mixture is added to a liter of water. A completely liquid dough, or rather a solution, will turn out in the ratio of water and gypsum one to one.
Mixing plaster yourself
When preparing a gypsum mortar, you need to know how to knead the gypsum correctly. The main thing here is to pour the powder into the water in the above proportions with constant stirring. And not vice versa. Moreover, it should be added evenly and gradually, avoiding the formation of lumps. You need to be aware that this may release a small amount of heat.
In addition, too long mixing is undesirable, because. leads to rejuvenation. To work with gypsum, a tool made of stainless steel or hard wood is recommended, it is possible to use special rubber spatulas, etc. As already mentioned, the time of work with gypsum mortar is quite limited. Therefore, the technology of working with gypsum, in addition to determining the “portioning” of its preparation, must also take into account the “layering” of processing associated with this.
It is necessary to prepare the already processed part (until it is completely hardened) with special notches. In case of a long break in work, the already applied and hardened layer should be slightly moistened before applying the next layer of material. If it is necessary to slow down the setting reaction of gypsum, you can use the so-called glue water (glue from the core or gelatin solution). The opposite effect can be achieved by adding ordinary table salt. In each case, it is worth experimenting with the proportions of the components.
Finishing materials made with the use of resistant polymer compounds save time and money during the construction phase, without creating pretexts for premature repairs. We sell finishing materials that meet European quality standards.
Made by strong brands
We cooperate with companies - innovators in the field of building materials. With those for whom the creation of a new experimental product is no less important than the improvement of an existing one. We value brands that invest in laboratory research. For example, Mapei spends 5% of its annual turnover on research and development.
For safe and sustainable homes
Sold products comply with European safety certificates. Construction Materials sold by Orso Bruno have a low emission of volatile substances. This means that they do not have a significant effect on the body. Most of our products are free of formaldehyde and solvents.
We are waiting on Barkhotskaya, 1a
"Orso Bruno" - shop finishing materials with direct distribution Mapei, Pergo, Ursa, Forbo Eurocol, Poleo. We also train clients at seminars and consult at the stages of work. Sold finishing materials are certified according to European quality standards. "Orso Bruno" - Support of your repair.
30. Gypsum mortar
The mortar usually consists of a binder and an aggregate. Gypsum is rarely used with aggregate. Basically, this is a pure gypsum dough of various densities. In practice, this dough is called gypsum mortar or simply gypsum. Gypsum mortar is prepared in various thicknesses. To prepare a liquid gypsum mortar for 1 kg of gypsum, take 0.7 liters of water, to prepare a solution of medium or normal density, 1.5 kg of gypsum per 1 liter of water, a thick solution - 2 kg of gypsum per 1 liter of water.
Gypsum mortar is prepared as follows. First, pour into the dishes required amount water, and then pour in a thin stream with thorough mixing the right amount of gypsum. With this preparation, a completely homogeneous solution is obtained, which is very important in stucco work.
If, however, gypsum is first poured, and then water is poured, then in this case lumps are almost always formed, which are very undesirable in stucco work.
Small portions of the gypsum mortar are mixed with metal spatulas, preferably copper or others made of stainless materials. Large portions of the solution are mixed with specially made wooden stirrers called whorls.
The whorl rod with two wooden, hard rubber or steel plates cut into it, when rotated between the palms, thoroughly stirs the solution (64).
The preparation of a gypsum mortar by the method discussed above is convenient in that the gypsum poured in a thin stream, passing through a layer of water, is quickly wetted and after 1 ... 1.5 minutes of mixing it turns into a ready-to-use dough. All this happens in the time before the start of setting of the gypsum.
It should be remembered that the thicker the gypsum mortar, the harder it is to work with it. It pours poorly and does not always fill tightly the entire form with a thin relief, and this is undesirable. With an insufficient amount of water, a gypsum mortar of uneven moisture is obtained, which sets unevenly and has a number of other disadvantages.
It is not allowed to mix the gypsum solution for a long time, as the gypsum begins to rejuvenate, and this reduces the strength of the product. It is especially dangerous to use such gypsum for the manufacture of gypsum lump molds, which will quickly fail.
For the preparation of large portions of gypsum mortar, it is recommended to use wooden utensils(buckets, large gangs, tubs). It is convenient to clean such dishes from adhering gypsum with a steel tool.
When casting large products, it is necessary to apply several portions of the solution. In this case, it should be provided that a new portion of the solution is poured onto the previous one until the previously poured gypsum mortar sets. In addition, it is desirable to scratch the surface of the previously poured gypsum. If these conditions are not met, the product may delaminate, and this will lead to its destruction.
During the preparation of the gypsum mortar, foam forms on its surface, which must be removed. If the foam gets into the product or into the plaster piece of the mold, then this place will be porous, and therefore weak.
To slow down the setting time of gypsum, setting retarders are used. The most common retarder is a weak adhesive solution (adhesive water), which not only slows down the setting of the gypsum mortar, but also gives the gypsum products increased strength. Common retarders are skin glue or gelatin. The higher the concentration of the adhesive solution, the longer the setting time and vice versa.
Usually prepare a solution of glue 25% concentration. The adhesive solution is poured into water, thoroughly mixed and gypsum is closed in this water. The adhesive solution should not be prepared for the future, but for one working day. In the warm season, it quickly rots. Liquid diluted glue can be stored in the refrigerator for 2-3 days.
A concentrated solution of glue is not only more effective than glue in its pure form, but it is also less required for the preparation of glue water.
To prepare the adhesive solution proceed as follows. 1 part by weight of dry animal glue is soaked in 5 parts by weight of water for 15...16 hours or more. After the glue is completely dissolved, 1 weight part of lime dough is added to it and the mixture is boiled over low heat for 5-6 hours, stirring occasionally. The solution foams strongly and to avoid this, pebbles are placed on the bottom of the dishes with a layer of no more than 2 cm. The resulting concentrate is diluted with water before use, and gypsum is closed on the resulting adhesive water. In terms of its effectiveness, such water is 2-3 times higher than water prepared with a conventional adhesive solution.
For casting large products, it is recommended to prepare gypsum dough in a large bowl or in two smaller ones and pour it simultaneously with reinforcement, pressing the reinforcement into the thickness of the gypsum layer.
If it is required to accelerate the setting of the gypsum mortar, then potassium alum is added to the water: 5 g per 1 liter of water. Alum is pre-dissolved in water.
Sometimes, to speed up the setting of gypsum, it is recommended to add table salt to it at the rate of 1 ... 2 g per 1 liter of water. The author of this book does not recommend doing this, since in such a plaster with high humidity heavily rusted metal fittings.
As already mentioned, gypsum products in the process of setting gypsum begin to warp. To minimize warping, it is recommended to mix the gypsum with lime water, which is prepared from boiled lime or lime paste.
To reduce the warping of gypsum products, mostly flat, do this. The product is laid with the back side on a flat workbench on a thin layer of poured gypsum, the newly cast product is ground to this layer and left for about 12 ... 16 hours or for a whole day. Then the product is removed from the workbench and laid on a flat surface to dry.
To reduce the warpage of gypsum and slow down its setting, borax is used, which is taken 0.5% by weight of the total amount of water on which the gypsum is closed.
To lighten the mass of gypsum products, they are prepared from gypsum mixed with sawdust, which slows down the setting of gypsum. Products can be made with the addition of sand to gypsum.
It is necessary to dry gypsum products in a warm room with a temperature of at least 16 ° C, but in no case in a draft, which contributes to warping of freshly cast products.
Frozen gypsum products after thawing are most often destroyed.
The simplest and inexpensive way strengthen the trunk of a tree of happiness or other crafts - plaster or alabaster casting. You can dilute gypsum or alabaster for topiary in a separate container or directly in a pot. The first method involves diluting a liquid solution, the second - a thick one (to hold the trunk). Each option has its advantages and disadvantages, but in practice both methods are applicable.
How to dilute gypsum - 2 ways to fill
liquid fill
Dilute plaster (alabaster) liquid solution appropriate for a small pot, where kneading a thick mixture will be problematic. In addition, liquid gypsum creates a perfectly flat surface, which is convenient for further decoration of the topiary. However, it will take at least 24 hours to dry (depending on the size of the pot). It is this way - optimal and most convenient for pouring topiary.
Dry gypsum is diluted with warm water in a ratio of 1 to 1, kneaded until smooth and poured into a pot to the desired level. The barrel is pre-fixed with plasticine to the bottom of the cache-pot. We recommend that you immediately wash the container and the whisk for kneading: gypsum mixture sets quickly, and alabaster hardens in a few seconds.
Thick filling in a pot
Thick plaster cast great for large, wide or shallow containers and is appropriate if you need to continue working on the tree of happiness as quickly as possible: the solution hardens in 3-4 hours.
Pour dry gypsum into the pot, slightly below the required level. Slowly add warm water, knead the solution until a thick, creamy mass is obtained. We insert the stem of the topiary in the desired position. It is very important not to overdo it with water: in a liquid fill, the trunk will collapse, and the drying time will increase.
in detail,