How to properly prepare clay for coating the oven

Over time, cracks can form in the masonry of a brick oven. This is due to a number of reasons:

• the influence of temperature difference
• uneven heating of refractory bricks bonded with chamotte clay
• poor quality putty used in the construction of the furnace
• furnace slump
• improper oven drying
• poor quality work in finishing
• condensation formed on the walls of the stove

  

Deep cracks pose a threat of collapse of the structure, as well as penetration of poisonous carbon monoxide, dangerous to human health and life. A natural question arises - how can you cover up the stove so that it does not crack? If only installing a new foundation will help to get rid of cracks resulting from the sinking of the furnace, then in other cases you can get rid of them.

How can you cover up the stove so that it does not crack

If the damage is small, superficial, you can remove the old finish from the bricks to re-plaster. If the damage is through, you will have to dismantle the damaged area and restore it.

Several options for what you can cover up the stove so that it does not crack:

• chamotte clay composition

It is a widely used material for restoring oven surfaces. Before use, fireclay clay should be kept in water for about two days.

• clay and sand composition

The cheapest option of the material, often used due to the ductility and viscosity of the mixture, as well as the durability after firing. For a high-quality solution, you will need any clay, the main thing is that it does not contain any impurities. You can prepare it as follows:

1. Clay is poured with water in a ratio of 1 to 3, after which it is infused for at least a day.
2. After it has been infused, it must be mixed with the addition of water. Then strain through a fine sieve and let it brew again.
3. A properly prepared mixture should have a thick consistency.
4. Mix clay and sand in a ratio of 1 to 2.5.

After mixing the solution, you can check its readiness by rolling a small ball. If it cracks, then there is not enough liquid in the solution. To increase the strength of the clay mortar, you can add asbestos, cement or gypsum to it.

Stove mix

• oven glue

This material can be purchased at the store and is durable and flame retardant. The composition of the kiln glue includes fireclay powder and refractory cement. It is of two types: solid and plastic mixture. The first type is rubbing the entire surface of the furnace, the second one is used to putty the seams and cracks. To prepare the glue solution, you need to dilute it in small portions, because it dries up quickly. For 1 liter of plastic mixture, 5 liters of solid must be kneaded. A plastic mixture is applied to the wetted bricks, all defects are repaired. Then a finishing coat is applied in the form of hard oven glue.

• special compounds for grouting stoves (you can purchase or make yourself).

If it is not possible to purchase a ready-made oven grout, you can prepare it yourself. For this, as in the first two cases, it is necessary to soak the clay, let it brew for 24 hours. Then add sand in a ratio of 1 to 4 and stir thoroughly. In the process of stirring, it is necessary to gradually add finely chopped straw, at the end add a pack of salt.

How to cover the stove with clay so that it does not crack?

All existing cracks must be knocked out with a chisel, the brick must be cleaned.If the surface is completely plastered, the seams must be cleaned to a depth of about 1 cm. Before covering the stove so that it does not crack, it is necessary to moisten all cracks, seams and cracks abundantly with water or a primer.

Stove

Before you coat the stove with a solution of clay, you need to heat it up to such an extent that its surface warms up a little. Then the stove is covered with a thin layer of liquid clay solution, left to dry for a while. Then the surface is reinforced: burlap or a thin metal mesh is applied, this will strengthen the plaster. The burlap is glued with an overlap, starting from top to bottom, and the mesh is attached with nails in the seams between the bricks. This sequence of actions is the same both for plastering the entire surface area, and when it is necessary to cover up individual areas.

Next, two layers of plaster, 5 mm thick, are applied. Too thick layer will be uneven and uneven. When the surface is dry, it is rubbed, and after complete drying, it is covered with a lime mortar. If you do not plan to whitewash the stove, you can add a little lime at the stage of mixing the clay solution, the clay will become lighter.

After the coating is completely dry (this will take at least 7 days), you can start heating it, but not earlier, otherwise it will continue to crack.

How to cover up cracks and plaster the stove?

Figure 4. Plaster over reinforcement mesh
In order not to crack the furnace, you need to competently approach its construction and operation. But if the cracks do appear, they must be eliminated as quickly as possible. Regardless of the type of mixture, the structure must be prepared before restoration. The surface is cleaned of dirt and debris, and cracks deepen and widen. If there are bumps and rushes on the base, they are knocked down.

Remember! If the oven begins to crack due to insufficient shrinkage, let it sit completely. Otherwise, after the repair, the structure will again be covered with cracks.

The hearth must be heated before coating. Due to the high temperature, the furnace materials will increase in volume. This will avoid re-cracking immediately after the post-restoration firing.

If there are few "seams", they are sealed locally before plastering. Otherwise, a holistic coating is used - the entire surface is covered with a liquid heat-resistant putty.

Scheme of work

Figure 5. Local filling of cracks
In general, the procedure is as follows:

• clean the base and perform other additional work;
• thinly cover the surface with a liquid mixture and allow the putty to dry;
• reinforce the base (or slots, if the repair is local); for this, a metal mesh with small meshes is used; fix the reinforcement with nails or dowels; as an alternative to the mesh, you can use burlap soaked in putty; it is preferable to patch up cracks with it;
• after the starting layer has dried, the hearth is plastered; the oven is coated in two layers - the thickness of each layer is not more than 5 mm.

The next steps are at the discretion of the oven owner. The structure is whitewashed or decorated in some other way.

Alternative ways

A more radical way to get rid of cracks is to install an aluminum frame or other metal. This requires two metal sheets, scissors for cutting metal, as well as corners. The size of the sheet is measured along the height and length of the surface to be repaired, cut out and applied to the furnace. On top and on the sides, the sheet is fixed with metal corners. After installation, the frame can be painted.

In addition, you can make ceramic tiles on the stove surface. It can also be attached on top of the frame, but if the cladding is of poor quality, cracks will still appear on the stove, only under the tiles.

The reasons for the smoke of the stove

The reasons why the smoke does not leave through the chimney, but spreads through the house, can be varied. The most common of these is a soot-clogged chimney. When the soot is removed, the heating is quickly adjusted and problems no longer arise.

If no one has lived in the house for a long time, then putty for the stove will not be needed. A stale chimney starts to work incorrectly, but the malfunction is easily eliminated. It is enough to warm up the riser by burning the paper, and the smoke will go along the right path.

If you do not know if the stove has worked before, then malfunctions in its operation may be caused by improper laying of the chimney or clogging of the channels with parts of the bricks. In this case, you cannot do without a major overhaul.

Well, and, of course, cracks in the chimney or in the stove itself lead to disruption of its operation and the appearance of smoke in living quarters.

Elimination of cracks on a metal surface

If a metal stove begins to crack, welding will be the best solution for repairing it. If it is impossible to use this option, you can prepare a heat-resistant mixture for sealing defects:

1. Clay-based mortar with the addition of metal filings, manganese dioxide, salt and borax in a ratio of 30 to 4: 2: 1: 1
2. A mixture of liquid glass and magnesite in a ratio of 3:10. Also, on the basis of water glass, a mixture of two parts of manganese oxide, zinc white and borax is made in one part. The glass is added until the desired consistency is obtained. Whitewash is used dry.
3. Colloidal sulfur, metal filings and ammonium chloride are mixed in a ratio of 1.5: 96: 2.5.
4. Based on natural drying oil: you need graphite, lead, manganese oxide in a ratio of 5 to 1 to 1. Lead is used in the form of a calcined oxide. Another solution with graphite, lead and chalk is diluted in a ratio of 12: 4: 3. Elimination of cracks on a metal surface

Why do furnace cracks appear?

Most often, problems appear in brick hearths. There are 4 main reasons for the violation of the integrity of the masonry:

• prolonged lack of heating in the house; if the stove stood in an unheated building for the winter, then cracks cannot be avoided - and not only in this structure, but also in the walls of the building;
• ignoring operational rules; The “fresh” oven must stand - the masonry mixture will set, and the structure should dry well; heating a damp hearth will certainly lead to the appearance of cracks;
• uneven heating of the furnace zones; the structure must be made so that the heat spreads over it evenly; otherwise, the line of the border of thermal contrast will become clearly visible - in this area the masonry will crack;
• the difference in the coefficients of thermal expansion of the masonry mixture and the masonry; the furnace material and the solution should be characterized by approximately the same indicators of thermal expansion, otherwise the surface will be covered with a network of microcracks; this is not the biggest problem - the slots are not visible on the cold design.

Figure 2. The resulting cracks along the masonry seams

These four causes lead to trouble that can be removed relatively easily with putty. But there are also more solid reasons:

• improper foundation design; if the latter, for example, does not correspond to the dimensions of the heat source, the furnace monolith will be broken; the oven will begin to crack even if the shrinkage of the base does not go according to plan;
• incorrect calculation of the physical characteristics of materials; for example, without a margin in the thermal seams, the metal structure will "break".

Reasons for cracking

Defects in masonry and coating may appear on the stove due to the following features:

• The use of low-quality or cheap materials. If the putty or grout has been mixed incorrectly, sooner or later it will crack. When working with a furnace, you should not save on coating work.
• Failure to comply with the finishing technology. When finishing the oven, it is very important to remember the intermediate steps, such as wetting the masonry and drying.You should not rush and apply the coating when the mixture has not yet dried out.
• Improper drying. Some craftsmen use building hair dryers or heat guns to speed up drying. This process is contraindicated in ovens, especially clay ovens. The structure must dry naturally to ensure uniform hardening.
• Drawdown. If the oven base or the first row of masonry was not made correctly, it will sag. Such a defect is more difficult to eliminate; in extreme cases, a complete or partial dismantling of the masonry may be required.

Drawdown is the most difficult defect to correct. It is never worth saving on the foundation of the stove. A good quality stove can survive even after the house is destroyed.

Note! Households often believe that the smoke in the room accumulates precisely because of the cracks. But sometimes the reason lies elsewhere.

Often, combustion products accumulate at home due to the following shortcomings:

• Chimney clogged. You can clean the smoke channel in different ways, but this should be done at frequent intervals.
• Clogging of the stove riser with brick chips. The brick gradually crumbles, which leads to clogging of the riser systems.
• Violation of internal masonry technology. In such a situation, you will have to completely redo the chimney.
• Hypothermia of the riser due to downtime. If the stove is not heated for a long time, it can smoke. To prevent this from happening, the first kindling is done gradually, heating the oven with paper and wood chips.

If you cannot independently determine the cause of the smoke at home, be sure to invite a professional for this. An experienced stove-maker will not only help to detect furnace defects, but also make an estimate of the work.