To prevent clay from cracking in the oven: rules for choosing a solution

Such a popular material as clay is actually a sedimentary rock. In the initial state, clay is a dusty powder, but when water is added it acquires plastic properties. The composition of clays can vary significantly, since in addition to the main components they contain various impurities. Typically, the base is made up of substances such as kaolinite, montmorillonite, and silica sand.

It is the composition that largely determines the plastic properties of the final material.

Why does clay crack?

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.

Fireclay clay

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.

Clay-sand mortar

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

What to do to avoid drying cracks

• First of all, of course, follow the technology for making ceramics.
• Secondly, to achieve a relatively uniform thickness of the walls and bottom of the product. If you are sure that the thickness of the walls and bottom is approximately the same, then this is already half the success. Sometimes you can remove excess thickness before finishing the job. If you did not have time to “finish” the product directly during creation, grooving the bottom can help, but for this the product must dry enough so that no deformation occurs during post-firing processing.
• Thirdly, artificially slow down the rate of drying of ceramics. In such cases, ceramics are placed to dry in cool rooms, but without drafts, since a sharp change in the rate of moisture evaporation from the surface can again lead to uneven drying. In any case, the batteries should be kept away from the ceramics, otherwise the drying will again be uneven. You can also artificially and slightly increase the air humidity in the room, or moisten the drying ceramics. But slowing down the drying speed is not always possible, especially when the workshop has only one room.

Therefore, the solution is often to accelerate the drying time of raw products while maintaining its uniformity. Sometimes the bottom of a ceramic product is dried with a hairdryer immediately after production. But here it is important not to overdo it, since a hairdryer can cause uneven drying of the outer surface of the work, which, on the contrary, should be avoided. If the goal is to achieve uniform drying, then proceed as follows

First of all, the product must be placed with its bottom on a moisture-absorbing surface; the classic option is a plaster circle or plaster stand. But plastic will not work. As a last resort, you can put regular newspaper, which, due to its “looseness,” absorbs moisture very well. Our next task is to ensure uniform drying of the walls and bottom. When drying, ceramics are sometimes placed in bags or covered with glass caps

If the goal is to achieve uniform drying, then we proceed as follows. First of all, the product must be placed with its bottom on a moisture-absorbing surface; the classic option is a plaster circle or plaster stand. But plastic will not work. As a last resort, you can put regular newspaper, which, due to its “looseness,” absorbs moisture very well. Our next task is to ensure uniform drying of the walls and bottom. When drying, ceramics are sometimes placed in bags or covered with glass caps.

For uniform drying, the thin wall needs to dry in the same amount of time as the thicker bottom. Therefore, the optimal option is when the walls of the product are covered (a plastic bag selected according to size is quite suitable), and air access is provided to the bottom. However, here you need to take into account the dimensions and not leave the drying ceramics unattended, periodically checking the uniformity of drying of the mass throughout the product.

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.

Dust

In order not to think about what to do if the plaster of the walls is cracked, it is necessary to remove dust from the surfaces being treated in advance and to the maximum extent possible. Its presence significantly impairs the adhesion of the liquid solution, as a result of which cracks will appear on the walls or ceiling, but not immediately.

It is worth noting that dusty sweeping of all walls and ceilings is not necessary. It is enough to lightly moisten them with a spray bottle, but only before starting finishing work, and not in advance.

Gypsum plaster: subtleties of use

The answer to the question of why gypsum plaster literally cracks immediately after drying sounds different than the situation with its cement sand counterpart. In this situation, the main sources of defects are:

1. Gypsum plaster, after drying, shows cracks where the treated surfaces were not roughly prepared. That is, cracks and voids have not been removed from them, into which gypsum will gradually penetrate, causing ruptures in the decorative layer.
2. Excess water is the reason why plaster on walls cracks, because gypsum mixtures are extremely sensitive to large amounts of moisture, which weakens their structure. This is especially true when diluting a slightly dried working solution with water.
3. Another important indicator is the thickness of the applied layer, which cannot be less than 0.5 cm, otherwise the moisture evaporates very quickly and the coating will inevitably “burst”.

It turns out that cracking of plaster is the result of an irresponsible attitude towards its use and non-compliance with the recommendations specified by the manufacturers. In general, this coating is quite easy to use, allowing you to make a cheap and high-quality base, and most importantly, an environmentally friendly base for a future decorative coating.

Clay plaster, the composition of which is simple and literally stands under your feet, is increasingly found on construction sites as a facing material for interior and exterior decoration. It is known that many centuries ago this was the main material for craftsmen, why do we still return to this experience?

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.

To make the clay more plastic, you can add glycerin to it.

To prevent the clay from cracking after drying, you need to clean it of various debris and small pebbles. To do this, you need to fill the clay with water, for example, in a basin. Once it is soaked, stir it until creamy and pass through a large sieve. Then you can leave it for several days to evaporate excess water. And in order for the clay to be more plastic, a little simple office glue (it is also popularly called liquid glass) is added to that mass (creamy state). I hope this method will help solve your problem. It was recommended by a professional ceramist on one website.

Best answers

Garni Pop:

Now listen to the correct answer from a professional. To "loosen" oily clay, add up to 30% fired clay. Sand causes problems during cooking, so it is not used. The mixture is called CHAMOT. This mass can be up to 10 cm thick if it dries slowly. The refractory shrinkage of fireclay is also small, which is why all monumental ceramics are made from it.

Veloria Granta:

yolk and possibly liquid glass

VASILY gets access:

add regular sand, and the proportions depend on the purpose

Doctor Man:

The drying method, plasticizer additives, including organic ones, depend on the purpose and further technological process: firing, coating, etc.

Vladimir Ivanov:

Guys, don't worry: Asbokroshka has been added.

Konstantin:

if the clay cracks when drying. it means it is “oily”. sifted sand is added. better than river...

Anastasia Babashkina:

Sand is sand, but there is a similar point: the clay needs to be finely crushed, all in parts, in order to remove all the fragments of stones, glass, and debris from it. Because it is because of foreign bodies that in half the cases the product cracks, and even during cooking it simply falls apart.

Reasons for furnace failure

Before looking for the best way to fix the problem, it is necessary to determine the causes of cracks. It could be:

• low quality of the solution used;

• violation of finishing technology;

• shrinkage of the brick structure;

• non-compliance with the rules for operating the stove.

If the stove sank due to an improperly poured foundation, smoke will pour out of all the cracks during the fire, the doors will no longer close tightly, and the brick will gradually begin to collapse. If such problems are discovered, you should immediately dismantle the entire structure, strengthen the foundation and lay it out again. However, in some cases you can do without radical measures.

All other reasons can be easily eliminated; it is only important to figure out how to cover the stove so that it does not crack.

Determining the extent of damage

Before getting started, you should consider the damage and determine the scope of work. If small cracks appear on the surface of the stove (even if in large numbers), to eliminate them you will need to remove the lining and clean the brick from the plaster.

For these purposes, you can use one of the following mixtures:

• made of clay and sand;

• from special grouts for ovens;

• made of fireclay clay;

• from oven glue.

Can’t decide what to cover the stove with to prevent it from cracking? Consider each option individually.

Types of cracks and features of their repair

Having figured out how to coat a brick stove when deformations appear, you need to familiarize yourself with the types of cracks that appear. Conventionally, they are divided into cobwebs and other types. The first type of cracks is classified as non-through, and therefore their treatment is much easier. To seal a sealed surface in this way, you need to follow a step-by-step algorithm:

• clean the surface and use a chisel to remove excess plaster and debris that is stuck in the cracks;
• then clean the surface nearby with a metal brush, sweep away excess dust;
• treat the prepared surface with a primer so that it penetrates into the cracks;
• mix cement with water until the consistency of liquid sour cream is formed, take a brush and treat the damaged areas with it.

Go over the cracks several times to ensure the damage is completely filled. Otherwise they will appear again very soon.

A mixture of clay and sand

Sealing cracks with clay mortar is the simplest and most economical way to restore a stove. At the same time, the quality of repairs will be no worse than using newfangled and expensive materials.

For these purposes, you can take absolutely any clay, the main thing is that it contains as few impurities as possible. After soaking, high-quality raw materials should become oily, homogeneous and plastic. Before covering the stove with clay (to prevent the surface of the fireplace from cracking in the future), pay attention to the specifics of preparing this solution.

How to make your own clay putty

Mixing the mixture is carried out in several stages.

1. Before mixing clay with sand, it should be soaked in warm water for at least 12 hours.

2. The wet solution should be thoroughly mixed and all lumps formed should be broken up. In this state, the clay combines with sand much better.

3. To prepare the working mixture, it is recommended to take 4 parts clay and 2 parts sand. The last component should be as clean as possible and pre-sifted. The volume of liquid depends on the degree of humidity of all components.

4. If you do not plan to whiten the stove, add lime to it at the stage of mixing the solution. All components are mixed until the consistency of sour cream. The finished mixture is covered with plastic wrap and left for 12 hours.

5. The settled solution is kneaded again. To check if there is enough water in it, take the putty in your palm and roll it into a ball. If it starts to crack when you squeeze it, add more water.

6. The oven should be lightly heated, water should be poured over the cracks, after which you can begin sealing.

7. To prevent the appearance of new cracks in the clay, you can add straw, but a more reliable way is to use a plaster mesh. If you apply a clay solution to a stove lined with such material, you can forget about the cracks for a long time.

Special putty is what you need to coat the oven with to prevent it from cracking

You can buy this mixture for eliminating cracks or make it yourself. Fireproof putty for stoves and fireplaces purchased at a building materials store is ideal for repairs. It perfectly withstands temperatures of 1000 degrees. Before applying it, the stove and cracks should be treated with water.

You can do the grouting yourself, following the instructions:

1. Pour clay into a container and break up the lumps.
2. Fill it with water and leave for 12 hours.
3. Pour sand into the clay and knead the mixture.
4. Finely chopped straw is added in small portions.
5. Add one pack of salt.

Sand and clay are mixed in a ratio of 1:4. For 4 buckets of clay you will need about 50 kilograms of straw.

Fireclay clay

Fireclay clay is often used to restore old stoves. This material is characterized by fire resistance, so stoves finished with it are reliable and durable.

You can purchase this type of clay at any construction market. It is sold in 20 kg bags and is not expensive at all. The working solution is prepared strictly following the instructions on the packaging.

Grout

To seal a brick oven, you can purchase a special grout. In stores there are various formulations that are produced specifically for these purposes. It’s worth noting right away that this option will cost you quite a lot, however, it is optimal for lining stoves and fireplaces.

If you cannot afford to purchase a specialized composition, prepare it at home. To do this you will need the following components:

The clay needs to be thoroughly kneaded, filled with water and set aside for 12 hours. After the specified time has passed, the required amount of sand should be added to the mixture. In the process of kneading the two components, finely chopped straw and salt are gradually added to them. Clay and sand are taken in a ratio of 4:1, with about 50 kg of straw and a pack of salt added for every 4 buckets of clay.

The resulting composition can withstand temperatures of more than 1000 degrees.

How to eliminate cracks in a metal structure?

The main solution to the problems of cracks in metal stoves is obvious - welding is used. But if this option is not suitable, you can use special fire-resistant putties.

Recipes for preparing mixtures are presented in the tables.

Table 1. Ratio of water-based mixture components

Table 2. Ratio of components of a mixture based on natural drying oil

Oven glue

To prevent the stove from cracking in the future, you can use heat-resistant glue to repair it. It belongs to the category of ready-made materials for finishing fireplaces, which are sold on construction sites. Its main qualities include resistance to high temperatures and durability.

This adhesive mixture contains fireclay powder and fire-resistant types of cement. Today, there are two types of glue - plastic and hard.

The first option is used for sealing cracks, and the second is intended for plastering the entire surface of the stove.

The main advantage of oven glue is its very fast drying, so you should not mix the solution in large quantities.

How to repair a firebox in a brick stove

If the question arises of how to repair cracks in a brick stove inside, you should try to minimize the heating of the walls using additional lining. This process involves the installation of special barrier partitions that absorb the entire thermal shock. The inside of the firebox is lined with one of the following materials:

• Cast iron. This is a fairly reliable type of raw material, it is distinguished by its durability and can withstand both loads and constant high temperatures. When introducing it, be sure to leave a small air gap between it and the brick wall.
• Steel. The material will last less than the previous one, since it tends to burn out quickly. An air cushion must be created behind such a layer. To maintain it at the same distance on all sides, a corrugated layer is laid. It will burn out after the first use of the stove, and the back space will remain free.
• Fireclay brick with markings ША-6 and ШБ-6. These models are not installed tightly to the stationary walls of the furnace. The approximate gap will be 7-10 mm. The brick is laid on fireclay mortar, which has increased stickiness.

Restoration of the firebox and removal of cracks in a brick kiln Source pechdoc.ru