Clay is a sedimentary rock. When dry it is dusty, but when moistened it becomes plastic. It contains one or more minerals of the kaolinite or montmorillonite group, but may also contain sandy compounds.

The clay is predominantly gray in color, but there are varieties in white, red, yellow, brown, blue, green, purple and even black. This is due to the substances contained in each type of clay. Depending on these same substances, the areas of application of clays are different.

Since this rock has high ductility, fire resistance, excellent sinterability and good waterproofing, it is widely used in pottery and brick production. However, often clay products develop cracks at the stage of modeling or drying, or at the final stage - firing. This can happen for several reasons: the clay is dry, the clay is “skinny”, that is, it contains a large admixture of sand, or, conversely, the selected variety is too “oily”.

Additives for clay mortar

To prevent the possibility of cracks forming on the product, it is necessary to choose the “right” type of clay from the very beginning. Blue and white clays are ideal for pottery. But sometimes the right choice of material is not enough.

If the product cracks due to insufficient moisture, the issue can be resolved by simply adding water to the clay solution.

However, sometimes a clay product cracks due to excessive “fat content” of the solution. Clays with high plasticity are called “fat.” When soaked, they give a tactile sensation of a fatty substance. The dough made from such clay is shiny, slippery and practically free of impurities. In this case, so-called “lean” substances are added to solutions made from such clay: “lean” clay, burnt brick, pottery scrap or sawdust and sand - ordinary or quartz.

But the opposite situation also happens - the product cracks due to the clay being too “thin”. This material is non-plastic or low-plastic, rough to the touch, has a matte surface and crumbles easily even with simple finger pressure. It contains a very large amount of impurities in the form of sand and earthy particles. In this case, it is necessary to carry out the reverse operation - add fatter clay to the “lean” clay or use other additives that increase the fat content of the solution, for example, glycerin or chicken protein.

There is another method - to soak the solution. Its essence is to add water to the solution and mix it thoroughly. The solution is allowed to settle. Water remains in the top layer, which is drained. The next layer contains liquid clay, and underneath it are unwanted additives. The liquid clay is carefully scooped out and poured into a basin, leaving it in the sun to evaporate excess moisture. As a result, plastic clay with the consistency of hard dough remains.

A home is a symbol of home comfort; it warms the body and soul. A good-quality stove will protect you from any weather conditions and create a comfortable atmosphere at home, so it is extremely unpleasant to find cracks on the surface of the stove. Putty for stoves is the only way to restore their original appearance.

Causes and danger of cracks

Violation of the integrity of the top layer or brickwork occurs for several reasons. In general, we can say that this is the result of the master’s mistakes. With proper selection of bricks, finishing materials and professional performance of the work, the formation of cracks on the stove, and especially cracks, is unlikely.

Most often, cracking occurs due to the influence of the following factors:

• non-use of the fireplace for a long time, especially in winter (due to sudden temperature changes);
• haste, manifested in the heating of a recently made stove;
• performing masonry using a method that creates large temperature differences in different places of the structure;
• inconsistencies in the thermal expansion capacity of bricks and mortar for laying;
• overheating or using fuel that produces significantly more heat than what the stove is designed for (for example, burning a wood stove with coal).

If the stove begins to crack for such reasons, then it is easy to fix the problem with your own hands. You need to properly seal the cracks, coat the surface - and the job is done.

It is much worse if the stove begins to crack due to an incorrectly made foundation or an illiterate choice of refractory materials. In this case, it will not be possible to simply seal the seams; you will need to lay the entire stove again.

Repairs cannot be delayed because cracks can leak carbon monoxide, which can poison residents. In addition, over time, the cracks increase, the stove can let flames pass through and completely fall apart.

Putty materials

Inventive people are ready to give advice on any matter, including the choice of materials for repairing stoves. Recommendations must be taken carefully, separating the wheat from the chaff.

A mixture of clay and sand

There are well-known putty compositions that have been tested many times over. You can use them without any doubt.

It is customary to cover stoves with clay. The material definitely inspires confidence, but first you need to check what type and grade of clay is suitable for making mechanically strong clay. The stove should be sealed so that it does not crack later.

The composition is prepared by mixing equal parts of clay and sand. Both components must first be sifted and separated from large impurities. Due to the fact that the clay composition in different deposits varies greatly, it is advisable to check the strength of the mixture.

Advice! You need to make balls from the slurry formed after adding water, let them dry well and examine them carefully. If cracking is not visible, the materials are suitable.

It would be advisable to tighten the inspection requirements by throwing dried cakes from a low height. If they did not collapse and successfully passed the tests, the chances of making a high-quality repair of the furnace increase.

When preparing homemade putty, monitor the condition of the wooden mixing spatula. The gruel should not stick to it. If clay adhesion is noticeable, it is better to increase the amount of sand in the mixture.

Of course, if possible, it is advisable to take . It is characterized by fire resistance and strength. You can buy it in building materials departments. Before use, fireclay raw materials should be kept in water for a couple of days.

Adding straw and horse manure

A popular folk method of preparing grout for stoves is to add chopped straw or chaff (husks, chaff) to the mixture of clay and sand. You need a lot of it. So, if 4 buckets were taken of clay, one bucket of sand will be needed, and straw - from 40 kg to 45 kg. You can hear advice about the benefits of adding salt to the grout at the rate of half a regular glass per bucket of the mixture. It is recommended that the quality and quantity of additional components be determined based on the local situation.

Important! You cannot use mortar with straw for laying. It is only suitable for covering surface cracks, for plaster.

Special formulations

If there are building materials stores nearby and you are willing to spend money, it is better to buy ready-made adhesives: soft or hard. The viscous solution is convenient for covering small cracks. Complete work can be done with solid compounds. Sometimes cracks in the masonry are sealed with a special heat-resistant sealant, and small cracks are filled with asbestos fiber.

Note! The finished product contains clay, sand, cement of proven quality, mineral and synthetic additives.

If the solution or paste is prepared correctly and the work is done correctly, the result is guaranteed by the manufacturer. What is important is that special putty compounds can be used if the stove is finished with tiles or decorative bricks. They are plastic, prevent the formation of repeated cracks and provide reliable adhesion to the masonry.

How to properly caulk a stove

The experience of repairing furnaces has a long history. Each area has its own characteristics of work. The tools you will need are a trowel and a grater (a grater, as a rule). Some people finish trimming the plaster directly with their hands. In general, the main stages of work are the same:

• First, the surface of the stove must be thoroughly cleaned and swept;
• then it is advisable to heat it; existing cracks can be sprinkled with water to moisten;
• after which a thin layer of putty should be applied. The main thing is not to overdo it;
• after the smeared layer has dried, if necessary, large cracks can be strengthened with reinforcement with a special mesh;
• then the surface is covered with plaster. It is advisable to do this in two stages, each time applying a layer up to 5 mm thick.

If the stove is covered with decorative finishing, then the coating is removed before covering the cracks. If necessary, the doors are reinforced with wire. Special adhesive compositions are prepared in small portions, since they can harden strongly.

Ultimately, by spending a little money, you can get rid of defects on the stove surface. The result will please the appearance and ensure safety for the home owners.

Sooner or later, any stove owner will ask how and with what to cover the stove to prevent it from cracking. Even if it is made of refractory bricks held together with fireclay clay mortar (such a structure can withstand severe temperatures), it can crack over time. The reasons may be as follows:

• uneven surface heating;
• violation of masonry technology;
• use of low-quality material.

Through cracks are dangerous for the health of the residents of the house, because carbon monoxide will penetrate through them from the furnace. Therefore, repair work must be carried out immediately.

Let's divide the process into three stages, you will need:

1. Diagnose the damage.
2. Prepare the solution.
3. Plaster the stove.

Damage diagnostics

First you need to inspect the extent of the damage and decide on the scope of work. If the damage is minor, then you can get by with superficial work - clean the brick from the finishing and plaster, seal the cracks and plaster the stove. If you observe large through gaps, damage to the cladding or masonry, you will have to disassemble and repair it.

Preparation of the solution

Regardless of the damage, you will need to prepare a mixture. Depending on the funds allocated for repairs and available materials, the following types of mortar can be used for repairs:

• from fireclay clay;
• ordinary clay and sand;
• grout for the stove (you can buy it or make it yourself);
• oven glue.

Proportions of components of different mortars for masonry and plastering of stoves

Let's look at these options in more detail.

Fireclay clay is the most used material for stove restoration. Fireclay has excellent fire resistance; stoves made with this material are durable and reliable.

You can buy fireclay clay at any construction supermarket (usually in 20 kg paper bags); before work, it is soaked in water and left to infuse for 2 days. This material is not very expensive; it is often used to plaster the stove.

Clay and sand

A solution of clay and sand is the cheapest option for restoring a stove. This method is often used, despite the low cost, the material is plastic and viscous, and after firing it is strong and durable. To prepare the solution you need:

1. Pour water over the clay and let it sit for more than a day. Proportions – 1 to 3.
2. Stir the clay, adding water. Then you need to strain it through a small sieve (3x3 mm) and let it stand.
3. Drain the water.
4. The thickness of the clay should resemble sour cream.
5. Mix clay and sand in equal proportions.
6. By stirring the solution with a stick, you need to determine its readiness. If there is a lot of clay on the stick, then you need to add sand (add 0.5 parts at a time). When small clots begin to stick to the stick, the mixture is ready.

Typically, one part clay requires two and a half parts sand.

VIDEO: How to knead clay for plaster

Oven grout

You can buy oven grout at the store or make it yourself. The store-bought option is quite expensive, but it is ideal for repairing stoves and fireplaces. Oven grout copes well with temperatures over 1000 degrees. Before applying the material, the oven and cracks are treated with water.

If it is not possible to purchase oven grout in a store, you can make it yourself. To do this, follow the instructions:

1. Pour the clay into a container and break up the lumps.
2. Fill with water and leave the solution for 12 hours.
3. Pour sand into the clay and knead it.
4. Gradually add finely chopped straw.
5. Add a packet of salt to the mixture.

The proportions of sand and clay are 1 to 4. If 4 buckets of clay were used, then about 50 kilograms of straw are needed.

Furnace glue

In construction stores you can buy special glue for stove repair; it is heat-resistant and durable. In the manufacture of such material, fireclay powder and refractory cement are used. There is a hard and plastic mixture. The plastic one is applied in the cracks, and the hard one needs to be plastered over the entire surface of the stove. The advantage of this material is that it dries very quickly. It needs to be mixed in small batches.

How to coat a stove

The coating method is selected depending on what you decide to coat the stove with (what mixture). Regardless of the material chosen, the brick will need to be cleaned of the decorative layer and plaster. Next, you can coat it with the solution.

If oven glue is used, you need:

1. Mix a small batch of plastic mortar.
2. Treat cracks with water.
3. Apply the mixture into cracks and crevices.
4. Mix the solid solution.
5. Coat the stove.

Almost immediately after this (the glue dries in less than half an hour), you can plaster the stove and apply a decorative layer.

VIDEO: How to plaster a stove so it doesn’t crack

If you decide to restore the stove using a solution containing clay, then the instructions will be as follows:

1. Stir the infused solution one more time.
2. Check the quality of the mixture. To do this, roll a ball in your palm; if it cracks, there is not enough water in the mixture.
3. Moisten the cracks with water.
4. Push the solution into the cracks. This can be done by hand and is safe for the skin.
5. Now you can plaster the stove.

The renovation is complete! But don’t rush to light the stove; this can be done after the solution has completely dried. Do everything according to the instructions and you can forget about cracks for a long time.

During operation, a crack may form on the surface of the stove masonry. This is caused by uneven heating of the material from which the masonry was made. Through cracks pose a danger to people because carbon monoxide enters the room through them. This means that damaged areas must be repaired immediately. But first, it is recommended to find out what needs to be done to prevent the clay from cracking.

The surface of the clay layer can crack for various reasons, and yet why this happens, consider the probable reasons and find out what to do to prevent the clay from cracking when drying:

• excessively thick layer. To avoid this, plaster with clay, applying a maximum two-centimeter layer. If there is a need to apply a second one, then the previous one should set well. In good weather, this takes at least a day. If it is intended to apply a plaster layer more than four centimeters thick, the surface must be reinforced with steel mesh;
• the plaster dries too quickly and begins to crack. Optimal conditions for this are 10 – 20 degrees Celsius. If the weather is hot, it is recommended to suspend work and moisten the walls more often. Perhaps the base of the wall quickly absorbs moisture. In this case, it is also moisturized abundantly;
• the solution turned out to be too greasy. Replace the clay or reduce its amount in the solution. The same applies to cement material.

Types of clay-based plasters

Let's consider the main options for plasters and the technology for their preparation.

Difficulties arise in the work, the bricks hold weakly in the masonry, the plaster layer is covered with numerous cracks. This is due to the fact that during the firing process the clay almost completely loses its plasticity, which must be returned to it when preparing the solution. In these cases, craftsmen recommend adding quartz sand or a special adhesive composition. The procedure for preparing the solution is as follows:

• you will need a pack of fireclay powder, which is poured into a container;
• water is added gradually until it covers the entire mass;
• it is necessary to wait three days for the material to infuse;
• after this sand is added. If the solution turns out to be thick, you can add water, otherwise the clay layer will crack when it dries;
• The mass is thoroughly mixed.

A properly prepared solution should resemble thick sour cream in thickness, only in this case it will not drain and will adhere perfectly to the surface. To speed up the drying process and take measures to prevent the clay from cracking, it is necessary to add cement at the rate of two kilograms per package of fireclay.

It is possible to purchase ready-to-mix formulations that do not require steeping for three days.

How to properly make such a solution so that the clay does not crack? First you need to sift the sand, for which you will need a sieve with a hole size of 2 - 3 mm. Its amount will depend on the degree of fat content of the clay.

The clay is pre-soaked. It is placed in a tank and filled with water, leaving for one to two days. After this, the mass is mixed and passed through a three-millimeter sieve. The result should be a solution that is similar in thickness to sour cream.

We start adding sand. As a rule, one and a half times more sand is required per liter of solution. But when the clay is oily and the solution is prepared in such proportions, then cracks will definitely appear. And with low-fat clay, the layer of plaster will not be durable.

The ratio of sand and clay should be accurately determined. For this purpose, take a liter of solution, to which sand is added in doses, while stirring the mass. The end result should be a material that easily slides off a metal shovel, but does not spread over it.

Clay-sand mortar with added fiber

What other clay solution can be used to cover the stove so that it does not crack? To do this, a small amount of cement is added to the working composition - a trowel per bucket.

If it is necessary to coat the stove to seal cracks, add simple table salt to the solution - up to five hundred grams per bucket. This gives the mixture strength and allows it to be more reliably held on the masonry surface.

Some craftsmen add a small amount of sheet asbestos soaked in water to the mortar mass. It is simply torn into small pieces and soaked in water. After a few minutes, the asbestos separates into individual fibers that reinforce the solution. The slurry obtained in this way is added to a solution of sand and clay, mixed and used as the first coating layer.

Nuances of testing clay plasticity

Different clays differ in their plasticity. There are:

• “fat” clays with high plasticity;
• material of medium ductility;
• “lean” clays with a low level of plasticity.

I determine the level of plasticity using a simple method. The clay is poured with water to turn it into a dough-like mass suitable for molding. The material is used to make cylinders seven centimeters long and 30 mm in diameter, the ends are pinched with fingers and slowly torn apart. Plasticity is judged by the shapes that the cylinder takes at the point of rupture, by its elongation. A plastic material is characterized by the formation of a long and thin neck, and if the clay is thin, the neck will be thick and short.

The level of plasticity is determined in another way. Flagella about twenty centimeters long and 1.5–2 mm in diameter are rolled out of the working material and bent into semicircles or pretzels. If cracks appear on the materials at this time, the clay is thin. Cracks that form during bending indicate that the clay is of medium plasticity, and fatty clay can be identified by the complete absence of cracks in the samples.

Advantages and disadvantages of clay compositions

The following features are highlighted as advantages:

• clay is a natural and environmentally friendly product;
• solutions perfectly absorb water and release it, which prolongs the service life of coatings;
• reasonable cost;
• the remains of the used solution are stored for a long time;
• the material perfectly protects the surface from mechanical impacts;
• the elasticity of the material allows it to be applied without any problems;
• Not only internal, but also external surfaces are finished with a clay mixture;
• using the solution, level and decorate the surfaces.

In addition to the positive aspects, clay-based plaster has a number of disadvantages, which explain most cases why clay cracks:

• There is no exact recipe for preparing the solution; craftsmen prepare the mixture using their own experience;
• there is a possibility that the surface will become covered with cracks;
• Such compositions are rarely used; there are few experienced craftsmen who know how to cover a stove with clay so that it does not crack.

Criteria for choosing a solution

Previously, classical solutions were used, taking into account combinations of heat resistance, increased heat capacity and thermal expansion equal to the brick material. To make such solutions, fatty clay was used.

Today you can purchase dry mixtures, certain types of clays and other compositions that simplify construction and repair work. It should be noted that not every such composition has the necessary characteristics - fire resistance, heat resistance, gas tightness.

The solution must be heat resistant, withstand high temperatures and exposure to chemically active substances. In addition, the gas density level must be quite high. The seams do not allow flue gases to pass through, but moisture must pass through the finished mixture for the stove to “breathe.”

Instructions for applying clay plaster

The work is performed in the following sequence:

• mortar cakes are applied along the wall at regular intervals, and the material is stretched over the entire surface with a wide spatula, a rule or a trowel;
• Evenness is checked using a level. If necessary, apply a second layer;
• the surface is given time to dry completely: from 1 to 3 months, depending on the season;
• finishing is being carried out. To do this, use a solution consisting of clay, cement and sand in a ratio of 1 to 1 to 3. The mixture is applied in a thin layer and leveled. After three to four weeks, the stove can be whitewashed with lime.

We now know how to coat a stove with clay so that it does not crack. But you should know that half the success depends on the correct preparation of the solution.

The heart of the house is the stove and it needs constant care. The stove (or - rough) can be stone, brick or metal.

Like a house, it is built to last, every detail is thought through. It bears the main temperature loads and periodically needs repairs. A thrifty owner will take care of preventative measures so as not to end up without a fire in the house. But troubles still happen, and the hearth cracks.

Causes of cracks

There are more serious reasons. A crack may appear if the physical characteristics of the material from which it is made are not taken into account. Red, refractory, refractory brick and stone expand differently when fired.

Without reserve in thermal seams, the masonry on cast iron appliances will begin to tear. In other cases, the foundation does not match the dimensions of the furnace or has shrinked unevenly. Then the oven will have to be moved over time.

Remedies

Stove lined with tiles For cladding, you can use porcelain stoneware, clinker tiles, terracotta, majolica or tiles.

If all the nuances and subtleties are observed, such decor will not require cosmetic repairs for a long time.

The most budget-friendly finishing option is plaster.

To plaster without cracks, you need to follow a certain sequence of actions, which are the same for both initial application and repair:

1. After installing the furnace, time must pass before final shrinkage and drying (from six months or more).
2. To coat, the oven must be heated strongly. The masonry will warm up and expand in volume, which will prevent cracks from appearing immediately after coating.
3. All surfaces must be thoroughly cleaned: remove the layer of old coating, clear out cracks in depth and widen them, clean off deposits from the masonry.
4. Cover with a thin layer of liquid putty and let it dry.
5. It is better to lay burlap or fine mesh metal mesh on top of the first layer. This will increase the strength of the plaster. The burlap is soaked in the same solution that is supposed to cover the entire surface. Then it is glued overlapping, starting from the top. The metal mesh is secured to the surface with nails, which are driven into the seams between the bricks.
6. If the repair is spot-on, then the cracks are covered very tightly with mortar and also lined with burlap.
7. the actual plaster. It is laid in two layers of 5 mm. Large thickness will lead to uneven and unstable coating.
8. The dried surface is rubbed to level it.
9. The plastered surface, after complete drying, is covered with lime or chalk whitewash. Heat-resistant pigments can be added to the whitewash solution.

How to cover it up

If brick (stone) and cast iron are held together by clay mortar, then it is advisable to prepare putty for cracks or plaster from it.

Clay solution. Prepared on water from clay and sand. There is no universal recipe.

The approximate ratio: the same amount of sand for one part of clay does not always justify itself. The required proportions can only be calculated experimentally due to the heterogeneous composition of the clays.

It is recommended to mix several solutions with different ratios. Make several rounds and cakes from each. When they have dried well (without sun and wind), you need to see what solution the cakes are made from cracking.

Continue the experiment with it: take the round pieces and drop them from a meter height. The solution from which the figures did not crack or crumble when dropped is the most suitable.

The solution will give minimal shrinkage if there is a lot of sand, but the strength will be greatly reduced. Water in the solution plays an important role: the more there is, the greater the risk of repeated cracking.

A high-quality solution must have a homogeneous structure. The sand must be sifted, and the pre-soaked clay must be strained. The water from such clay is drained after settling.

Most often, fireclay powder, lime, gypsum or cement are used as additives to increase strength. Rich folk experience suggests mixing clay mortar with wood ash and salt to give it greater strength.

Ready-made mixtures. If the rough structure was built using factory mixtures, then cracks must be repaired and plastered with mortar. It is prepared according to the manufacturer's instructions and used in the same way as clay.

Metal Furnace Processing

The elimination of cracks in metal furnaces deserves a separate topic. Usually welding is used for this.

However, if welding is unavailable for some reason, there are many recommendations for making heat-resistant putty for metal furnaces.

You can make solutions with water from the following components:

• clay, metal filings, manganese dioxide, salt, borax in a ratio of 30:4:2:1:1;
• magnesite and liquid glass take 10 to 3;
• metal filings, ammonium chloride, colloidal sulfur – 96:2.5:1.5.

On natural drying oil:

• graphite, lead, manganese oxide in a ratio of 5:1:1;
• clay, zinc white, manganese oxide – 4:2:1;
• graphite, lead, chalk – 12:4:3.

On liquid glass - from manganese oxide, zinc white and borax with a specific gravity of each component of 2:1:1. Glass is added to the required consistency. Using dehydrated glycerin or ethylene glycol, the putty is prepared with lead litharge in a ratio of 1:9. Clay and white for heat-resistant putty must be used in dry form, lead - in the form of calcined oxide.

To ensure that the stove does not cause unnecessary trouble, even at the planning stage it is necessary to provide for all design features and select materials that guarantee warmth, peace and security in the house.

Watch the video in which an experienced user explains in detail the process of preparing a clay solution that can be used to cover the stove so that it does not crack: