Architectural gypsum. Architectural elements - is it better to use expanded polystyrene (foam) or plaster? Technical characteristics and properties

Gypsum facade stucco - what is it?

Plaster stucco molding- this is an element or group of elements for decoration, intended for the design of facades of buildings and structures. The style of exterior design may vary greatly. Just imagine - classic, art deco, hi-tech, baroque and more - all these are completely different directions, but almost always this decor is made of plaster.

Facade gypsum stucco molding is a separate branch in architectural decoration, so it is absolutely clear that it has a certain prehistory. Surely everyone has heard about the masterpiece of gypsum architectural construction - the Peterhof Palace in St. Petersburg. The stucco molding used to decorate the facades of Peterhof has delighted us for several centuries and still inspires many people to achieve architectural delights.

Advantages of gypsum facade decor:

Where is gypsum used?

Gypsum decor can be used for both facade decoration and interior decorative work. GC "DecorFasada" offers services for the design, production and installation of gypsum decor for:

• house facades,
• interiors.

Difference between plaster decor for facade and similar for residential premises only in the additional treatment of the first with a special solution that does not allow corrosion and destruction under the influence of the climatic conditions of our region. Facade decor made of gypsum after treatment with a special composition does not differ in shade from gypsum stucco molding for residential premises.

Plaster stucco in interiors.

Since facade decor made of gypsum and stucco in interiors are different topics, where only the internal processes in production and installation are similar, we have allocated a separate page of our website to gypsum interior stucco.

- (Greek gypsos) a mineral that is a crystalline hydrate of calcium sulfate; used in surgical practice and dental prosthetics for the manufacture of plaster casts, casts, etc. Medical encyclopedia

In the construction industry, gypsum is in second place after cement-sand mixtures. The unpretentiousness of the material, excellent environmental friendliness and relatively simple technology of use have become the reason for the massive use of building gypsum for the production of safe blocks, finishing elements and even interior items.

Production of gypsum mass

The raw materials for the production of gypsum for construction purposes are natural deposits of gypsum stone in the form of anhydrous anhydride - calcium sulfate, its dihydrate modification CaSO 4 * H 2 O, as well as a huge amount of industrial waste from the chemical and metallurgical production sector.

The gypsum production technology consists of three sequential operations:

• Purification, fractionation and pre-grinding of raw materials;
• Heat treatment at different temperatures, from 160 o C to 1000 o C;
• Final grinding of the heat-treated gypsum mass to a powdery state, drying and packaging of the building material in hermetically sealed packaging.

The general technology of gypsum production divides the binding gypsum material into two categories - quickly setting, or semi-aqueous material, and slowly setting gypsum stone. The first group includes construction and high-strength molding gypsum material, the second group includes less durable anhydride cement and highly calcined stone, called estrich gypsum in the old fashioned way.

In the process of heating to 180 o C, the raw material - two-water gypsum stone breaks down into two modifications, after separation on sieves, high-strength α-gypsum is used for the manufacture of gypsum stone, blocks and forms, β-modification is divided into several categories, the most viscous, with high bending strength, used for construction purposes, the rest as decorative and auxiliary material.

Types of gypsum stone

In addition to the chemical composition, the properties and characteristics of gypsum largely depend on the structure of the raw material. For example, in addition to natural alabaster stone, which has a pronounced polycrystalline structure, a fibrous type of calcium anhydride, selenite, is used for production.

All types of gypsum, from building to decorative or architectural, are obtained by varying the content of selenite, alabaster, raw gypsum stone, finely ground waste calcium sulfate, heat-treated at different temperatures. After fractionation of the raw material according to the degree of grinding, gypsum is divided into three groups:

• A - quick-hardening or alabaster materials;
• B and C - mixtures with a hardening time of up to 15 minutes;
• G - gypsum building materials.

The finer the grain, the faster the material hardens.

Construction or high-quality gypsum

For construction work, not the most durable grades of gypsum are used; uniform hardening and relatively high water absorption, which provides the mixtures with high plasticity, are considered more important. For the production of building materials from gypsum, putties, and gypsum plaster mixtures, the β-modification of medium fineness is used.

Due to special wetting and setting-retarding additives, you can work with gypsum mortar almost like you would with a cement-sand mixture. This reduces gypsum shrinkage and the risk of cracks in the building material.

High strength gypsum stone

Finely ground α-modifications of raw gypsum are used for the manufacture of finished building finishing elements, for example, artificial facing stone, plasterboard sheets, fire partitions and slabs for laying flooring.

High-strength gypsum mixtures can be used to finish walls of frame buildings, ceilings, and interior parts. Per 100 kg of heat-treated raw material there is no more than 20% of the high-strength fraction, so the material is quite expensive and is rarely used in its pure form. Most often, high-strength building gypsum is the basis for the manufacture of fire-resistant or architectural materials.

Polymer stone-gypsum

The idea of ​​adding polymer additives to the gypsum mass has been used for quite a long time. Polymer gypsum is obtained in two ways:

• Addition of water-soluble polymer compounds that improve the fluidity of gypsum and wetting of grain. A water-soluble polymer, for example, polyvinyl acetate emulsion or an aqueous solution of carboxycellulose, increases the resistance of the material to impacts and alternating loads;
• Saturation of the surface of the finished casting from building gypsum with volatile polymer compositions, most often based on polyurethane or polypropylene.

In both cases, a thin plate of building gypsum turns out to be quite elastic and at the same time light. From polymer gypsum you can easily make an inexpensive finish that imitates expensive types of wood in texture and pattern.

Cellacast gypsum material

The widespread use of gypsum material is hampered by one of its inherent disadvantages - the high fragility of gypsum. This prevents the production of thin screeds or shells from plaster. Therefore, the building material is saturated with special reinforcing microfiber, the surface of which is treated with polyurethane.

As a result, the strength of the building material increases by 40-50%, and resistance to bending loads by 150-200%. Celacast plaster is widely used in medical institutions for applying fixing bandages for fractures and severe injuries of the extremities.

Sculptural or moldable gypsum material

Ordinary building plaster, after slight modification with polymer resins and dihydric alcohol, turns into a mass from which a model, impression, or bas-relief of any complexity can be made.

Gypsum molding material cannot be diluted with water, as is usually done for building gypsum. In the kit, a special water-alcohol based solvent is added to the white or beige-gray finely ground powder. Thanks to the use of a solvent, it is possible to achieve almost zero shrinkage of the material. Therefore, souvenirs and casts of objects with minute carvings or engravings are often made from sculptural plaster, for example, when copying rare coins, artifacts, and ancient awards.

Acrylic gypsum block

It is quite easy to turn building plaster into a homemade version of homemade earthenware. It is enough to knead with the preliminary addition of one-component acrylic resin. The result is a light and very hard casting that can be processed by carving, grinding, and drilling. For example, make decorative stucco moldings or vases imitating antique porcelain from building plaster.

In the construction industry, mixtures of acrylic and gypsum are used to make wall cladding from gypsum blocks and to form the rough base of self-leveling self-leveling floors.

Polyurethane gypsum material

The use of non-woven polyurethane fabrics and fibers with a specially treated surface has made it possible to create a fundamentally new material for the manufacture of immobilizing bandages, tourniquets and pads that fix limbs and body parts in case of severe injuries.

Unlike cellocast plaster, polyurethane gypsum material has high strength and sufficient casting flexibility to reduce discomfort from its use. Polyurethane material is obtained from construction materials using a special procedure for reseeding the ground mass and separating the largest grains of the same size. As a result of processing the rough mass of building gypsum, a casting with huge pores is obtained, providing free access of air to the body tissues.

White gypsum stone

Construction gypsum serves as a raw material for the production of so-called white or dental gypsum materials. The white color is obtained through deep purification of the raw materials, removing sulfur oxides, sulfates of heavy metals, iron, and organic impurities, which usually color building gypsum in a grayish-beige color.

Mixtures are made from finely ground white stone to form impressions necessary for subsequent prosthetics or treatment. White stone differs from building material in a whole bunch of additional qualities:

• The gypsum casting must not contain irritating or toxic materials;
• No shrinkage of white gypsum molds;
• Minimum water absorption;
• Rapid setting of the gypsum matrix.

For your information! White plaster typically provides very high impression properties, which is why it is often used to make jewelry casting molds. Parts weighing at least 3g in size are poured into a mold made of building plaster.

Fine-grained gypsum

Reducing the grain size of building gypsum can significantly improve its two main characteristics:

• The strength of the material increases under the influence of bending loads;
• Higher flexibility for thin castings.

A casting based on finely ground α-gypsum grain can show a strength of 350-400 kg/cm 2 . The only limitation that has to be taken into account is high shrinkage, so building gypsum based on fine grains is used for repair work and the manufacture of high-strength coatings.

For your information! From fine-grained gypsum, after vacuuming and high-temperature curing of the mixture, a thin sheet can be easily produced, almost identical in appearance and properties to packaging cardboard.

Liquid gypsum material

If alcohol glycol solutions are used instead of water to mix building gypsum, the material can be stored in an unchanged state for a long time. Liquid gypsum material is used to perform repair and thermal insulation work. After adding an aqueous solution of calcium chloride and table salt, liquid gypsum can be pumped under pressure into cracks in walls or floor slabs. To repair foundations, liquid is used only in combination with polymer resins, for example, polyurethanes.

Waterproof gypsum stone

For all its advantages, ordinary building gypsum remains quite sensitive to moisture or condensation. Moisture-resistant gypsum board material is made using thermosetting polymer powders, and sometimes simply finely ground polystyrene, added to dry building gypsum at the stage of forming the slab.

After curing, the building boards are subjected to heat treatment, and the material acquires water-resistant qualities.

Fireproof block

Heat-resistant or even fire-resistant gypsum block on an industrial scale is made on the basis of ordinary building gypsum and fire-resistant additives. Such material can even be made with your own hands using the following recipe:

• 30% of the weight of high-quality building gypsum and the same amount of water;
• 15% ground ash or fireclay dust;
• 4% aluminum oxide, you can take washed skinny white clay;
• 2% each of quicklime and ground iron dioxide.

For your information! If building gypsum is required for fire safety class G1, then the complex composition can be replaced with finely ground quartz sand, however, such gypsum stone will not withstand heating above 600°C.

Architectural

Most often, building gypsum for architectural work means ordinary molding gypsum modified with polyurethane fibers or polystyrene. This is a relatively soft material, and you can use it to make a model or cast simple stucco elements without any problems.

Real architectural gypsum for construction work is made on the basis of gypsum stone, fired at a temperature of 800-1000 o C. The result is a very hard, viscous building gypsum that does not absorb water well. If you follow the mixing technology, you will get a gypsum casting with a very hard and at the same time wear-resistant surface.

Unlike polystyrene architectural plaster, from which craftsmen now like to assemble 17th-century style finishes, real stucco for exterior walls was cast from high-fired building plaster. The difference is impressive. Polystyrene stone lasts for at most 10 years, old hardened plaster has withstood almost two hundred years in the climate of St. Petersburg.

Brands of gypsum mixtures

During the production process, the heat-treated mass after grinding is fractionated according to density and particle size. In accordance with GOST No. 125-79, the material is divided into four groups or twelve grades.

The first group includes ordinary gypsum materials G2-G7, with a strength of 20-70 kg/cm2, the second group includes low-shrinkage mixtures G10, G13-16. The third group is high-strength G22-25, the fourth group includes gypsum mixtures with special properties, for example, fire-resistant or highly porous blocks and stones.

Properties of building gypsum

A typical gypsum block used for construction purposes is a highly porous mass; the volume of air channels can reach 50-55%. The density of building gypsum stone is 2.6-2.75 g/cm 3 , for a bulk mass of 900-1000 kg/m 3 in a pressed but uncured state, the building mixture can be compacted to 1400 kg/m 3 .

Dry hard gypsum stone can easily withstand heating up to 450-500 o C; 100-120 minutes after the start of thermal exposure, the surface begins to peel off until gradual destruction. The thermal conductivity of gypsum block is 0.259 kcal/m deg/hour at room temperature.

Grinding degree

The raw building gypsum obtained during treatment with superheated steam under a pressure of 1.5-2.5 Atm is conventionally divided into three grades

• The first grade of material corresponds to the fraction that leaves 918 units on a sieve with a hole density of 918 units. per cm 2 no more than 15% of the initial volume. This is the most active and durable fraction of building gypsum;
• To the second grade include more viscous masses with residual moisture of no more than 0.1% of the mass; after passing the sieve test, no more than 25% should remain on the mesh;
• The third grade, especially finely ground building gypsum, leaves no more than 2% of the mass on the sieve.

It is clear that the finer the grain of calcium anhydride, the faster water absorption occurs and the more hydraulic bonds are formed between individual grains of building gypsum, the stronger and harder the gypsum stone becomes.

Compressive and bending strength

The tensile strength for building gypsum of the first category is determined as 55 kg/cm 2. The second category, after completion of the hardening process, must withstand a static load of 40 kg/cm2. After about four hours, the hardened building stone after drying should withstand up to 200 kg/cm2.

The flexural strength for dried stone is 30% of the static compression for unreinforced material and 65% for reinforced mass. An increase in stone moisture content by just 15% can reduce strength by 40-60%.

Normal density, water requirement or water-gypsum ratio

The amount of water required to form internal bonds between grains depends on the chemical composition. For α-gypsum based on hemihydrate, 35-38% of water by weight of building gypsum stone is required, for weaker viscous β-hemihydrate, from which the bulk of building gypsum material is produced, 50-60% of an aqueous solvent is required.

The thickness of the gypsum mixture in the first minutes corresponds to wallpaper glue, after 10 minutes. This is already thick sour cream, and after another 5 minutes. - viscous, crumbling mass. By introducing additives based on FFA, alum gels or even lime, the density can be stabilized and the overall water consumption of the building material can be reduced by 10%.

Reinforcement of gypsum boards and blocks

Despite the internal homogeneity of the hardened gypsum mass, the bending strength of blocks and slabs is considered insufficient. It is especially difficult to work with thin slabs and sheets. Often, the fall of building gypsum cladding from a wall to the floor means destruction and puncture of the material.

Building gypsum blocks are reinforced with chopped polyester fiber, thin-sheet panels are strengthened by the introduction of fiberglass and fluff pulp.

Gypsum as a binding material

Dry gypsum mixture has a high water absorption capacity, for example, hemihydrate α-gypsum has a surface area of ​​up to 6000 cm 2 /g, and the weaker β-modification has twice as much. A small amount of 3-5% gypsum mixture added to lime or cement mortar can increase viscosity by 15%.

A relatively simple and effective way to correct the viscosity of any mortar, but it is worth considering that the water absorption process develops progressively, so the residual viscosity of the mixture will be formed no earlier than 15 minutes after adding the material.

Plaster setting

High-quality gypsum has a high hardening speed; in practice, for freshly fired building material of the first category, the setting process should begin within 4 minutes after dilution with water. For gypsum material of the second category, the curing process according to the standard should begin no earlier than after 6 minutes. It is clear that due to the absorption of water vapor from the air, gypsum, even when carefully packaged in a waterproof shell, loses activity, therefore, the standards for gypsum material limit the start time of hardening to 30 minutes. Anything more than that is already considered unusable. The total setting time from the beginning of mixing to the transition to a solid state should not exceed 12 minutes.

The setting time of building gypsum is limited to a period of 3 hours. An exception is anhydrite cement, for which the setting limit is set at 24 hours. If a building gypsum block gains full strength after 3-4 hours, depending on the temperature and mixing conditions, then for an anhydrite gypsum masonry mortar the limit is set, as for cement -sand mixtures, 28 days. A sample of hardened anhydrite gypsum binder must withstand a compressive load of 50-150 kgcm2.

Hardening of gypsum

The process of binding water and gaining strength with building gypsum can be accompanied by expansion of the hardening mass. The more anhydride in soluble form in the chemical composition, the greater the degree of expansion. For example, hemihydrate can increase the size by 0.5%, and for β-modification the casting material increases by 0.8%.

This leads to self-strengthening of the building mass, but it is not very convenient if you need to maintain maximum accuracy of the cast, so the effect is combated by adding 1% lime or Pomazkov materials. During the drying process, building gypsum shrinks, so stone masses of great thickness are always loaded with internal stresses.

Construction gypsum: application

A high degree of versatility and very simple preparation technology have become the reason for the enormous popularity of gypsum stone. The material is perfectly processed, cut, drilled, and glued. At the same time, in the mass of building stone there are practically no aging and degradation processes, like in plastic or polymer-mineral boards.

Gypsum blocks and plasterboard sheets have become one of the most popular options for wall cladding in residential premises. Firstly, the high porosity of gypsum makes it possible to regulate humidity naturally. Secondly, building gypsum has good sound insulation and low thermal conductivity.

The material is easy to paint and plaster; if necessary, using wax mastic, the walls can be made moisture-proof to water and condensation, but relatively transparent to water vapor.

Preparing the mixture

The process of preparing a gypsum solution begins with sifting the dry mixture through a sieve, it is best to use DK0355, this is approximately 400 holes per square centimeter. Next, the required amount of water is heated to 40 o C and poured into the mixer container. Gypsum is added in small portions to the water, and then a thin film formed on the water surface is immediately broken with a trowel.

In theory, the strength of a cast gypsum block depends on the consistency of the mix. The thicker the solution, the smaller the size of the pores and anhydride crystals. When there is an excess of water, the crystals quickly increase in size, which leads to intense pore formation.

Material storage

The only reliable way to properly store dry gypsum material is to use glass jars with a sealed lid. Dry calcined gypsum can be used to drain containers or floors, but to restore its original qualities, the material must be deoxidized with an aqueous solution of sulfuric acid, remove water by calcination and re-grind into dust to a grain size of 0.01-0.003 mm. Industrial polyethylene packaging provides reliable storage of the dry mixture only for the first two months. Dry plasters based on gypsum material in paper bags after opening must be used within 3 days.

Plaster substitute

The only material that can replace building gypsum is considered to be alabaster, both in its pure form and with the addition of lime or polymer emulsions. Dry lime in an amount of up to 1% must be added at the stage of preparing the building mixture for mixing. The material is intensively ground on a metal or stone surface to make the batch as homogeneous as possible. If it is necessary to prepare a casting mold, then white clay and flake graphite can be added to alabaster at the rate of 2% and 1%, respectively.

What is the difference between plaster and alabaster?

Both materials are a product of firing natural sulfuric anhydride, but due to the large amount of impurities of iron oxide and aluminum oxide, the alabaster material is obtained with a slight reddish tint. Unlike gypsum, alabaster sets in 3-5 minutes, so any castings made from alabaster stone have high surface hardness. Alabaster takes mechanical loads worse and gives a high degree of expansion followed by shrinkage.

Size and weight of white sand-lime brick

Construction gypsum is a fine powder of extremely white or light gray color, obtained by grinding and firing (or exactly the opposite - firing and grinding) natural gypsum stone. The advantage of this material over others is its very fast setting and the same hardening.

The beginning of setting occurs within 5 minutes after its application. In some cases, these advantages can turn into disadvantages, therefore, to slow down the setting and hardening reactions, lime mortar, water-soluble animal glue, etc. are added to it.

Areas of application of gypsum in construction

During the hardening process, this material is capable of increasing in volume, which is characteristic only of prestressing cements, but, unlike the latter, our object of discussion is a fairly light material and can be used in interior finishing work.

Its undeniable advantages include environmental friendliness, non-flammability, and the ability to “breathe”. The disadvantage of the building material is its relatively low strength and water resistance; in addition, it is quite easy to scratch.

This material is used for finishing plastering work, the manufacture of any products, drywall, molds, castings, as an additive to other binders, wood concrete, for ventilation ducts, etc.

Also, chemically or using traditional technology, they obtain high-strength gypsum. This is a material of the highest quality, used where all its unique characteristics are needed, and the strength of ordinary building gypsum is not enough.

Types of gypsum - why is there such diversity?

This material has a large number of varieties. And each has found its practical application in life. There are the following types of gypsum:

• Pure material combined with a mixture of lime and blast furnace slag is called waterproof plaster. In addition, to increase the water resistance of products, surface-active organic additives (sulfite-alcohol stillage) can be added to its composition. And the use of an aqueous solution of certain resins (carbamyl), in the form of a mixing liquid, can provide fairly high levels of mechanical strength and water resistance;
• Lightweight plaster obtained by using special technologies in the process of processing conventional raw materials. This material is used in the manufacture of high-quality ceiling moldings and wall panels;
• When the raw material is heated to approximately 140 °C, it turns into a white or grayish powder. This material is perfectly soluble in water, it is used for the manufacture of high-strength, construction and other gypsum compositions. We can say that the received semi-aqueous gypsum– this is a semi-finished product for further processing of this material;
• Raw ground gypsum used as an additive in the production of cellular concrete, aerated concrete, and for soil treatment.
• Fine-grained gypsum needed in construction for filling joints, joining slabs, finishing, etc. This material is also called a translucent type of gypsum. It is part of construction alabaster;
• Architectural plaster, another name is molding, intended for the production of stucco molding, decorative stone, restoration of building facades, production of souvenirs and various forms.

The above examples are not all types of gypsum, but, as can be seen from what is written, it has firmly and permanently entered many areas of construction. This is due to its excellent characteristics and environmental friendliness.

The online store of building materials "MasterSmesi" offers to evaluate high-strength gypsum G-16, which is often called sculptural or architectural. Its strength indicator is 160 kg/cm 2. In addition, G-16 gypsum has a fine grind, which makes it suitable for decorative finishing.

Areas of application of G-16 gypsum

• production of dry construction mixtures;
• production of artistic details for the home (decorative plates, cornices, bas-reliefs, sculptures, etc.);
• production of molds in the ceramic industry;
• in medicine (traumatology and dentistry).

A product unique in its properties, which is used both for construction and for the manufacture of stucco molding. Gypsum G-16, like construction gypsum, has astringent properties. The G-16 has found wide use among the people. It is often used for grouting putties, primers and for sealing seams.