What and how to plaster stoves and fireplaces: refractory mortar + finishing

More than just a decorative element, plastering stoves and fireplaces is crucial to assuring their longevity and safety. The correct plaster shields against the extreme heat these structures produce while also improving the appearance.

Selecting the right refractory mortar is essential for a job well done in plastering. Because of its high temperature resistance, this kind of mortar is perfect for stoves and fireplaces. Without it, the plaster may eventually break down or deteriorate, jeopardizing the structure’s appearance and functionality.

After choosing the appropriate mortar, applying plaster requires meticulous planning and attention to detail. It’s a task that calls for perseverance and the appropriate methods to guarantee a seamless, long-lasting finish.

What is the need for plastering?

A stove or fireplace should never be left unfinished. This is due to a few factors:

• attractive appearance;
• creation of an additional sealed layer: after all, even if the brick joints crack, the likelihood of carbon monoxide leaking into the room is significantly reduced;
• hygiene: leveling the masonry joints prevents dust from settling on them.

Because of this, it is preferable to plaster over stoves and fireplaces or cover them with stone, porcelain stoneware, or ceramic tiles that withstand heat. The most common choice is the first one. Ultimately, the plaster mixture is reasonably priced, presents well, and has a considerable lifespan.

I suggest watching Alexander Zalutsky’s video course if you want to become a professional decorator of stoves and fireplaces with twenty years of experience. The technologies of the tile, stone, and plaster foci are thoroughly examined in the lessons. Just the expert’s knowledge and useful advice without water?

Than to plaster: select a refractory solution

Heat resistance, temperature tolerance, high elasticity, and resistance to crack formation are the fundamental requirements for mixtures used to decorate residential furnaces and fireplaces. Typical building solutions are inappropriate in this situation. Plastering furnaces and fireplaces requires the use of the following kinds of heat-resistant mixtures:

• clay-lendrum:
• Cement-Gliny:
• clay-gypsum;
• mixed using several binders.

The rate at which the solution hardens is controlled by the manufacturers by adding various plasticizers and moisture-retaining additives to these mixtures. Because they set more slowly, working with them is more convenient.

Two categories of refractory compounds are typically produced. For rough primary finishing, use the first. Up to 10 mm of thick layer application is possible. The second kind of mixtures is exclusively utilized for the last stage of surface leveling. A layer like that is up to 3 mm thinner. The finishing solution’s composition is altered with finely dispersed components to produce a perfectly smooth and level surface that is ready for painting or covering with decorative plaster.

Terracotta is a commonly used mixture in prefabricated heat-resistant plasters for stoves. It is composed of functional additives and kaolin fireclay dust. tolerates temperatures as high as +400 °C.

The work is done between +5 °C and +35 °C. One kilogram of plaster should be mixed with 250 milliliters of water, then left for fifteen minutes. The mixture is used again and then left for sixty minutes. The mixture is applied in layers of up to 10 mm at a time, with a consumption of 10 kg/m2. You must wait until the previous layer is totally dry if you need to apply a second layer. To prevent the plaster from cracking in this situation, natural ventilation is preferred and accelerated drying is not permitted.

Is it possible to use a gypsum mixture?

Ordinary gypsum solutions should not be used in their pure form for finishing brick stoves and fireplaces because they do not contain clay additives, which makes them inappropriate for use in high temperatures. After such plastering, a smooth surface will rapidly develop cracks all over it, rendering the stucco useless.

Purchasing pre-made mixtures would be the best course of action if you lack experience preparing solutions. In this instance, you can be positive that the surface will be able to tolerate exposure to both high and low temperatures.

It’s crucial to use a refractory mortar that can tolerate high temperatures without cracking when plastering stoves and fireplaces. This plaster ensures that the structure is safe and aesthetically pleasing by providing a decorative and protective finish. The secret to longevity and a smooth finish that blends in with the interior decor of the room is proper application.

Making heat-resistant plaster with your own hands

Making a mixture for plastering is not hard, but there are a few subtleties you need to be aware of. Thus, we will require:

• clay is a must: due to its high thermal conductivity, the solution will be able to withstand high temperatures; it is important that the clay is not too fat, since such a solution will crack when drying; but excessively lean clay is also undesirable, because it has a low plasticity index, so it is problematic to get a smooth surface with it;
• sand, providing strength to the solution;
• lime: a plasticizer that increases adhesion (adhesion); it must be slaked in advance so that unslaked particles do not destroy the surface;
• cement: since the main disadvantage of clay is low strength and slow drying, a small amount of cement is often added to the solution;
• fiberglass or asbestos, used to enhance strength characteristics; such additives are especially important when creating thick layers when leveling strong slopes; in this case, the wall is additionally reinforced with shingles and wooden slats.

There are numerous ways to make plaster that resists heat. The ratios listed below are appropriate for manual mixing:

• a mixture of clay, sand and asbestos 1:2:0.2;
• a solution prepared on the basis of sand, lime, asbestos and, of course, clay: 2:1:0.1:1;
• when using cement with the addition of clay, sand and asbestos: 1:1:2:0.1.

The dry clay lumps are first crushed, then they are submerged in water for a minimum of one day. It is best to place a film over the container to stop the liquid from evaporating too quickly. Make sure to remove any leftover water after that.

The combination of sand, clay, and other additives is thoroughly mixed without the addition of water in order to ensure uniform distribution of the components. The easiest method to accomplish this is using a drill with a mixer attachment. Make sure to strain the completed mixture through a sieve to prevent lumps.

Please be aware that skilled stovemakers do not always adhere to the exact measurements when preparing a refractory mortar. After all, the clay’s plasticity and fat content determine how much of the constituents are added. Attempt to roll it into a tiny ball and place it on the ground. Normal clay must have some tiny fissures but not crumble away entirely.

Use a wooden stick to measure the solution’s fat content after adding water. It is normal if it adheres to it in an even layer of two to three millimeters. An excessively thick layer suggests insufficient sand. Add clay if it slides off the stick.

Stoves and fireplaces should not be plastered right away after construction; instead, the structure needs to shrink and dry thoroughly for about a month. First, heat the house’s fireplace or stove to between 50 and 60 degrees.

Oil stains and efflorescence are removed from the masonry surface prior to beginning work. In order to prevent the brick from drawing moisture from the mortar and losing its firmness, dust must also be removed and the area must be moistened with water. When wetted, the seams shouldn’t be too thoroughly removed. It’s best to start small when doing this work because water on the surface of a slightly heated oven dries quickly.

Plastering (video)

Consequently, you must carry out the following actions in order to plaster a stove or fireplace correctly:

• to obtain a flat surface, beacons are first placed on it using a building level – mortar slaps; further work is carried out only after they have dried;
• at the same stage, if necessary, corner steel pads are also attached, which serve to protect the corners of the structure from crumbling;
• if such pads are not provided, since clay is prone to chipping, the corners are brought out with a slight rounding;
• to strengthen the surface, you can use burlap or steel plaster mesh; it is attached to ordinary 100 mm nails driven into the seams between the bricks; self-tapping screws should not be used in this case, since the plastic sleeves will immediately melt when kindled;
• the solution is applied with a trowel or thrown onto the surface and leveled with a float;
• It is not necessary to immediately apply a layer of solution immediately, it is better to do this in several stages, applying, and then drying 2-3 hours layers, the thickness of each of which is 4-5 mm; In this case, the surface will turn out to be more durable;
• small cracks that form during drying are quite typical for such solutions, they are embroidered with a painting knife and plaster; do not forget to wet the surface with water when working;
• lastly, a thin finishing layer is laid on a completely dried wall.

The plastered surface will crack if the stove or fireplace is heated before it is completely dry. It takes three days to carry out the first kindling. Additionally, the stove or fireplace’s heating shouldn’t use more than half of its power.

The following video illustrates the technology of work:

Clay plaster

Can be covered in ceramic tiles with a base made of cement plaster. Cement to sand ratio of 1:14. Because there is significantly less draft in a fireplace chimney than in a stove chimney, it does not heat up as much.

For extremely heated surfaces, lime-cement mortar works well. While it is more difficult to repair, it is far stronger than clay.

Chimney lining outside the house

The chimney’s brick walls are subject to significant temperature variations, particularly during the winter. There was cold air on one side and hot smoke on the other. Over time, the brick is ruined by this temperature differential. Sulfur and nitrogen oxides are other substances found in stove smoke. When water vapor condenses on the walls of a cold chimney top and combines with oxides, acids are created. The brick pipe is destroyed by both the temperature differential and this acidic condensate.

A portion of the chimney outside the house needs to be insulated in order to avoid this kind of situation. This is accomplished by installing a frame, covering everything with tin sheets, and installing insulation on top of it. Plastering the brickwork alone won’t cut it.

To ensure durability and safety when plastering stoves and fireplaces, the proper materials and techniques must be used. Refractory mortar is essential for shielding these constructions from intense heat and for giving them a smooth surface on which to be finished.

Adding the right finishing touches to your stove or fireplace, such as plaster, tile, or stone, gives it a polished and useful appearance. Appropriate application guarantees both durability and a pleasing appearance.

By doing these simple tasks, you can improve the appearance and functionality of your fireplace or stove, turning it into a lovely and useful feature of your house.

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