Perhaps no cozy private house can be imagined without a good stove or fireplace. In addition, to this day, many people living in non-gasified areas are simply forced to heat with firewood. On the one hand, this is the most environmentally friendly heating method, and on the other, it is economically profitable. Prices for alternative fuels and electricity maintain a steady upward trend, so it is necessary to look for the best way out of this situation.

Many people want to learn how to lay stoves, and this is due not only to the desire to save on heating in winter. Practical skills gained in the course of training can be an excellent help in the development of personal business. The demand for furnace work is growing every year, creating prospects for a fairly high income.

Heat resistant, heat resistant, fire resistant - what's the difference?

Novice stove-makers often experience some difficulties associated with the correct understanding of terminology. With regard to mortars for oven masonry, the greatest confusion arises with the concepts of heat resistance, heat resistance and fire resistance of the material. These parameters are fundamental in the furnace business, so now we will try to clarify their meaning and clarify the understanding of this issue.

Heat resistant called a material that can withstand heating to high temperatures. At the same time, during its subsequent cooling, the structure and chemical composition are preserved and there are no irreversible changes in shape. In addition, heat-resistant materials, when heated, are still able to withstand the initial specified physical stress without the risk of possible fracture.

Main property heat-resistant materials - resistance to temperature, provided that the original mechanical properties are preserved. Heat-resistant substances and compounds have an order of magnitude less thermal expansion than heat-resistant ones. Such materials are used in the design of not only furnaces, but also mechanical devices operating in extreme temperature conditions, while being subjected to powerful dynamic effects.

Finally, refractory materials are heat-resistant or heat-resistant compounds, which, among other things, calmly withstand the action of chemically active (often aggressive) substances contained in gaseous substances. Specifically, in the case of stove masonry, this can be smoke or products of thermal decomposition of fuel.

All solutions and materials used in the construction of furnaces must be heat-resistant and refractory. This requirement applies even to those elements that, in the normal operation of the stove, do not heat up by more than four hundred degrees. None of the standard building mixtures meet these parameters.

The main elements of the furnace and the requirements for the solutions used for their masonry

The choice of solution for work must be carried out depending on which part of the stove it will be used for masonry. Using the diagram below, let's take a closer look at each of them.

1. Reinforced concrete base (1) of the furnace foundation, which is also called a pillow or root. It is made according to standard technology, however, without fail, in order to avoid unpleasant consequences, it must be physically separated from the foundation of the house itself. The need to comply with this condition is explained by the differences in the degree of shrinkage of the building and the furnace in it.
2. Waterproofing layer (2). To create it, roofing material is perfect, which must be laid on top of the foundation in several layers.
3. Actually, the furnace foundation itself (3). Since it is not exposed to powerful thermal effects, it does not require the use of particularly heat-resistant mixtures during masonry. At the same time, the reliability of the entire structure depends on the assembly quality of this furnace element. There are cases when, due to mistakes in laying the foundation, it was necessary to completely disassemble the stove and remake it in a new way. For work, complex, three- and more-component cement-lime mixtures are used. Well, as the main building material, red solid brick is best suited here.
   

   For the manufacture of compact stoves or stoves with a large base area (for example, a Russian stove), you can also use a conventional lime mixture.

4. Thermal insulation layer with fire protection blind area (4). It is made of mineral cardboard or asbestos sheet, on which a sheet of iron is placed on top, covering the entire structure with a finishing layer of felt cloth impregnated with so-called clay milk (this is a solution of very thinly diluted clay).
5. Heat exchanger (5), which stores the energy released during the burning of wood. It is one of the main parts of the so-called furnace body. During kindling, it rarely heats up above six hundred degrees, but it is very actively influenced by the smoke and other gaseous substances released during combustion. It is not uncommon for destructive acid condensate to settle on the inner surface of heat-storage masonry. Special bricks are used here: stove, grade M150, ceramic corpulent red. The bricks are fastened together with a simple one-component clay mortar. It should be noted that the term "simple" refers only to the composition of the building mixture. Its preparation is a rather laborious process, the features of which we will consider later.
6. The hot part of the body of the stove is also called the combustion chamber (6). It is exposed to the average chemical influence of gases, but it heats up to very high temperatures, up to 1200 degrees. For masonry, so-called fireclay bricks and a clay-fireclay type refractory mortar are used.
7. Chimney source (7). It is made of the same brick and fastened with the same mortar, which is indicated in paragraph 5, since this element of the furnace is subjected to the same temperature and chemical effects as the heat-accumulating part of its body.
8. Chimney "fluff" (8). Its task is to create a flexible mechanical connection that connects the ceiling and the chimney itself. Allows you to avoid a situation in which a sinking of the ceiling is possible. The fluff can be repaired separately; it does not require a complete disassembly of the entire structure. Brick for masonry is taken with a standard stove, and the mortar is used of a lime type.
9. Fire cut (9) is a special metal box filled with a non-flammable heat-insulating substance.
10. Chimney pipe (10). This element is susceptible to wind and precipitation. It heats up poorly, so the pipe is laid out of standard red brick. However, for greater reliability and heat resistance, a lime solution is used.
11. Chimney flare (11). It is made from the same materials that are used for laying the main part of the pipe.

Types of mortars for oven masonry and their main properties

After reviewing the previous paragraph of the article, you may have noticed that it is recommended to use your own type of mortar, which is most suitable for work, for laying different components of the furnace. Let's take a closer look at each of them.

Clay oven mortar

Clay mortar is the cheapest building material. It can usually be obtained and prepared at home by yourself. We will consider this process in detail later, since the preparation of composite components is quite laborious in itself and requires a separate instruction. The strength of the clay mortar, as well as its heat resistance, is average. The composition is able to withstand exposure to temperatures up to 1100 degrees Celsius without consequences. With regard to refractoriness, here clay is practically unmatched: it does not ignite, and only hydrofluoric and fluorine-antimony acids can dissolve it. It also has absolute gas density indicators. The stove folded on a clay solution can be easily reassembled, since the mixture moistened with water will again deteriorate. In addition, such material is suitable for work for an almost unlimited period of time: a container with a solution covered with a damp cloth will not dry out even after a couple of months. On the other hand, this is also its disadvantage: clay is completely unsuitable for laying outside the room.

Video instruction. Correct mixing of clay mortar

Lime and cement-lime building mixtures

Lime mortar, in any case, will cost more than clay. To prepare it, you will have to purchase a special lime dough or lump quicklime. It should be noted that quicklime will allow you to save money, but later this will come back to haunt with serious labor costs: preparing a solution from boiling lime is a meticulous process, because you need to extinguish all the particles to the last. If quicklime is present in the mixture, then the masonry seam can then burst. The mortar itself has a reduced heat resistance and fire resistance. It is able to withstand inactive flue gases with temperatures less than five hundred degrees. In comparison with clay mixture, it has a lower gas density. On the other hand, lime mortar does not absorb atmospheric moisture, so it can be worked with outside the building. The ready-made mixture is suitable for use for a relatively short (relative to clay) period of time: it can be used to put the oven on from one to three days after mixing.

The cement-lime mortar costs more than the usual lime mortar. However, this is partially offset by its increased strength. On the other hand, the resistance to heat is about two times lower here: the cement-lime mixture will withstand temperatures only up to 250 degrees without consequences. The gas density index of the solution is low. It is, in most cases, used for the construction of the furnace foundation. It dries up rather quickly, therefore it remains suitable for work only within an hour after preparation.

Clay-fireclay and cement-fireclay mortars

Clay-fireclay the solution has all the properties of an ordinary clay mixture, but to a greater extent it is heat-resistant (its maximum operating temperature reaches 1300 Celsius). This material, of course, is more expensive than clay, since for its preparation it is necessary to purchase special fireclay sand. Clay-fireclay solutions, for the most part, are used for the construction of a furnace furnace.

Cement-fireclay the solution is quite expensive, since it requires the use of high quality ingredients. In terms of strength, the mixture has equal indicators with cement-lime, while it is heat-resistant as clay-chamotte mix. On the other hand, it has an average level of fire resistance. However, it is quite enough for laying the furnace part of the furnace. The shelf life of the finished cement-chamotte mortar is about forty minutes. It should also be noted that the mixing of the components in it is not done manually.

The names of multicomponent mixtures for masonry are usually composed in such a way that the name of the strongest binder is in the first place. Moreover, the percentage of its content in the solution can be the smallest. For example, cement in a cement-lime mixture is 10-15 times less than lime.

Two terms used above require a separate explanation: "gas density" and "fireclay". Let's understand their meaning.

The term "gas density" refers to the ability of a material to pass gaseous substances. If the solution has a high gas density, then it will not let particles out and they will not, due to diffusion, get inside the heated room. It should be noted that gas tightness and hygroscopicity are not mutually exclusive concepts. Water vapor molecules are smaller and more mobile than smoke particles. A good quality solution must combine both qualities in optimal proportions, both gas tightness and hygroscopicity. The stove must "breathe" and, at the same time, not let the smoke inside. It is these requirements that are key for the formulation of kiln building mixtures.

As for the second concept under consideration, "chamotte" is a special refractory and heat-resistant material. It is produced by deep firing a mixture of special clay (the so-called "high-alumina"), zirconium compounds, garnet crystals and some other components. Deep firing differs from ordinary firing in that it provides for the continuation of heating the substance even after the complete separation of all crystallization water from it, up to sintering and the formation of lumps.

How to save on masonry materials?

The answer to this question, it would seem, is quite obvious: it is necessary to make the most of the materials at hand, which can be obtained for free right at the construction site of the furnace. In our case, on our own we can get the following components: clay, sand and water. But, as practice shows, in reality, everything is far from so simple. You can't just take any water, mix it with the first sand and clay that comes along, and as a result get a good high-quality mixture for masonry. A number of serious requirements are put forward for each component for creating an oven mortar. Let's find out more about each of them and learn how to select all the necessary components.

Clay. How to distinguish quality clay from other minerals?

Quite often, broken clay can be purchased cheaply from local stove-makers, but we do not recommend that you go the easy way. Such material is usually heavily contaminated with organic impurities. Subsequently, they will rot and decompose, deteriorating the consistency of the mixture and the quality of the finished joints. It is much more profitable to find good clay in the surrounding area and dig it up yourself. The difficulty lies only in learning to distinguish quality deposits from polluted ones.

Clay, in essence, is a mixture of aluminum oxide Al 2 O 3 and silicon oxide SiO 2 (in simple terms, sand). The main determining parameter for clay is its fat content. In turn, the strength of its structure, plasticity, indicators of adhesion (ability to adhere to other surfaces), hygroscopicity and even gas density will directly depend on it. As a standard, the fat content of clay containing 62 percent alumina and 38 percent sand is taken equal to 100%, and the fat content of pure sand without impurities is taken as the zero point of reference - 0%. To knead the oven solutions, we need clay with an average fat content, because the seams from a material of too high fat content will crack during drying. "Lean", or as it is also called, "skinny" clay also does not differ in strength.

Clay has several twin fossils that are often confused with it. However, kiln work with other mineral materials is not possible, so it is important to be able to distinguish them from what we need.

Shale and marl. The material is a brittle rocky rock. It lies in horizontally discernible layers that are rounded at the edges. In addition, if you take a sample of shale for a sample and break it, then the shale structure will be clearly visible on the resulting cut.

The most difficult to identify is bentonite, also known as bentonite clay (benthoclines). It is a valuable mineral, but it is completely unsuitable for use in ovens. Sometimes bentonite of bright colors is found, practically identical in appearance to the clay we need.

Bentonite clay, consisting of sodium-calcium compounds, montmorillonite and other impurities, has found its application in pharmacology, medicine, perfumery, wine-making and even in mining. The uniqueness of this mineral compound lies in its ability to absorb moisture. Bentonite saturated with water can without consequences increase in its volume by a factor of one and a half, passing into a gel-like state. But, unfortunately, it does not possess the properties of ordinary clay, such as fire resistance, gas tightness and heat resistance. It is quite simple to distinguish bentogline from the building material we need. It is enough to take a small test sample and place it in a glass filled with water. After a short period of time, bentonite will absorb moisture and noticeably increase in size. After waiting a sufficient period, you will be able to contemplate the transformation of the sample into a bentonite gel, which looks like a jelly, somewhat similar to jellied meat. Clay in water will not turn into anything like that.

In the figure below you can see a schematic section of the soil structure typical for our country. Clay located in the upper layers of the earth is heavily contaminated with organic impurities. Above, the main layer of clay deposits is covered with so-called loam - a layer of soil with a significant admixture of alumina and sand. In the diagram, loam is marked in yellow. Actually, the main layer of clay has uneven fat content: from above it is minimal and grows as it goes deeper into the soil.

We will determine the fat content of clay using a special test. Raw materials for analysis must be collected after passing through a layer of loam. In this situation - starting from five meters from the surface of the earth.

The clay sample itself is very simple: we take in our hands a lump of material with a volume of half a fist. We wet our hands with water and begin to knead it, like plasticine, gradually giving the sample the shape of a ball.

After the ball is ready, we begin to slowly press it with two flat plates on both sides exactly until the first cracks form. If you managed to squeeze the ball by at least a third of its diameter, then this clay is quite suitable for our tasks. We take another five kilograms of material into the bucket and carry it home for further tests, which we will talk about later.

Water. Home water quality analysis

It is necessary first of all to check the quality indicators of the water that we plan to use to create the furnace solution. For work, only the so-called "soft" water is suitable, or at least water with medium hardness. Hardness is measured in units called German degrees. One such degree means that there are 20 milligrams of calcium and magnesium salt in each liter of the tested water. The kiln solution can be mixed only if the water hardness is below ten such degrees.

What sand is suitable for oven masonry? Sand preparation

As for the sand, there is no need to take samples of it. Near clay deposits, you can always find interlayers of white quartz sand and yellow, containing feldspar. The first one is suitable for creating any furnace structures, and the second one can be used in the masonry of all elements, except for the hottest part - the firebox. Remember that preparing the sand for work will require a significant amount of water. That is why you should take care of the solution of issues regarding uninterrupted water supply in advance.

The sand accumulated on your own must first be passed through a sieve with a mesh size of 1-1.5 millimeters. This allows you to get rid of various large debris and get the required set of fractions. The biggest problem for self-excavated sand is organic impurities and various living microorganisms that live in it. Sand must be cleaned of them, otherwise the seams of the masonry may deteriorate over time.

There are many industrial methods for cleaning sand, but all of them are associated with significant energy costs. In order to save money, we will use a simple and affordable way of flushing.

For the manufacture of the purification apparatus, we need a piece of pipe 15-20 centimeters in diameter. Its height should be about three times its thickness. We fill up a third of the volume with sand and supply water from below under high pressure. The power of the water jet must be selected in such a way that the washed sand swirls, but does not flow into the drain located on top. After clean water flows into the drain, wait about ten more minutes and finish the procedure. The first batch of cleaned sand is ready. It remains only to dry it.

The method of sand filtration by the washing method also allows us to remove from it various inclusions of alumina that we do not need.

Determination of basic proportions. How much sand, water and clay should be in the solution?

An important step in preparing the mortar is to determine the optimal proportion between sand and clay. After we bring home the clay sample selected according to the above algorithm, it is necessary to divide it in two. Set aside the first half, and divide the second into five identical pieces again. We place each of them inside a separate dish and add water (hardness up to 11 German degrees) there, about a quarter of the volume of the clay itself.

Next, we leave the clay to soften in water. Typically, this process takes approximately 24 hours. After a day, stir it thoroughly and pass it through a sieve with a mesh size of three millimeters to sift out large lumps.

Re-put the container with the strained solution on the sludge. When a muddy slurry (the so-called "sludge") appears on the surface of the solution after settling, we remove it by pouring it onto the ground.

That's it, now you can start adding sand to each container with prepared clay. This must be done in the following proportions:

• First container - do not add sand;
• The second is one part of sand to four parts of clay;
• The third is two parts of sand into four parts of clay;
• Fourth - 3 parts of sand and four parts of clay;
• Fifth, sand and clay are added in the same amount.

Adding sand to each of the containers must be done gradually, in small portions, in several approaches (optimally, at least three and no more than seven). Stir everything very carefully. Do not rush to add the next portion of sand before the previous one is completely evenly dissolved in the mixture. A well-mixed clay-sand mortar is quite easy to identify: just try to grind it between your fingers. If the roughness of individual grains of sand is not felt, then everything was done correctly.

The next step in preparing the clay-sand mortar will be the production of prototypes. We take clay in each of the five containers and do it in turn:

• Two bundles of about 35 centimeters in length and a centimeter and a half in diameter;
• We mold a ball with a diameter of five centimeters;
• A round clay cake with a thickness of 12-15 millimeters and a radius of 7.5-8.5 centimeters.

As a result, we will have exactly 20 samples on our hands, which must be marked and left to dry inside the building. For proper drying, samples should not be exposed to drafts and direct sunlight. Usually tourniquets dry out in a couple of days, but cakes and balls may take up to two dozen days. If the ball does not wrinkle, and the cake has ceased to bend in half, then the material is completely dry.

When the samples are ready for testing, we proceed to the next classic experiment to determine the fat content of the clay solution. To do this, we wrap a clay tourniquet around the handle of the shovel, then tear it apart and observe the results:

• The greasy clay marked in Figure G (from German “greesy” - greasy) will practically not crack, and when the rope is torn in half, the break will have tear-shaped ends.
• Clay of normal fat content (marked as N) will have a cracked dry top layer and, after breaking the rope, its thickness at the separation point will be equal to about a fifth of the original. These are the samples we need to select.
• Dry (skinny) clay, designated as L (from German "Lean" - lean), will be marked by the maximum number of deep cracks and, when broken, will have the largest area at the point of separation of pieces of rope.

As a rule, after the selection is carried out, several (usually 2 or 3), at first glance, suitable samples remain.

Dried balls and cakes will help us to carry out the final "clay casting". We drop samples from a meter above the bare floor. The most durable of them will indicate the required consistency of sand with clay. If, after falling from a meter, all the samples remain intact, we begin to gradually increase the height until we can determine the most durable of them.

The next step in the preparation of the mortar will be to calculate the required ratio of water to the proportion of sand in the mixture. The physical limits within which a clay mixture will have normal fat content are quite wide. Our main task, since we put the stove for ourselves, is to make the most robust structure, with excellent indicators of gas tightness of the material of the connecting seams.

First of all, we sift the clay remaining during the test fence. Squeeze the clay through a fine mesh sieve so that it mixes evenly with the sand. Add the required amount of prepared washed sand. We learned the proportions of sand and clay earlier thanks to our experiments. We begin to add water and mix the solution. Remember that the water must meet the hardness parameters that we talked about earlier.

• A torn hollow indicates that there is not enough water (Fig. 1)
• If the hollow immediately behind the trowel begins to float, it means that we have gone too far with the water (Fig. 2). Defend the solution, remove the sludge in a separate bowl. The difference in volume between poured water and squeezed out sludge will show us the optimal proportion required.
• In the case when you have guessed right away with the required amount of water, the trowel will leave a clear, well-distinguishable even track with highlighted edges on the surface of the mixed solution.

Kneading the clay solution according to the calculated proportions. Test of strength.

To find out whether our solution will be sufficiently strong and possess the necessary degree of adhesion will allow the so-called cross test. This final experiment will show how correct the results of all our preparatory material checks were and how well we cleaned the constituent components of the kiln mixture.

To check, we need a couple of bricks, one of which we lay flat on the ground and cover its largest plane (the so-called "bed") with a thin layer of prepared test clay solution. We put a second brick on top, and, hitting it with a trowel, let the mixture dry for about ten minutes. After that, we grab the brick located on top with our fingers and pull it up. Having raised it to a certain height, we shake the structure by weight: if the lower brick did not come off at the same time, then all the preparatory work was carried out carefully and we correctly calculated all the proportions for the oven solution.

You can also familiarize yourself with the principles of preparing clay solutions for laying a furnace by watching the videos below:

Video: Preparation of mortar for laying ovens

Video:How to prepare the composition of the clay oven mortar