Aerated Concrete Walls: How And With What To Plaster Them, Tips For Plastering

2023 Author: Philip Bishop | [email protected]. Last modified: 2023-08-25 07:54

• Finishing features
• Choice of method and material
• Unsuccessful options
• Breathable finish
• Vapor barrier finish
• Features of work
• Plastering process
• The final stage

Plastering aerated concrete walls inside a residential building is one of the best options to preserve the heat-saving properties of the enclosing structures.

The use of aerated concrete blocks as a building material is almost ideal for low-rise housing. Private houses built from them have such advantages as low weight (and, therefore, do not require the construction of too strong foundations), low thermal conductivity and an affordable price. At the same time, an increase in the humidity of the blocks leads to a deterioration in its heat-saving characteristics and to a heavier structure. To protect the walls, aerated concrete wall plaster is required - sometimes external, but most often internal.

Finishing features

When performing internal plastering of aerated concrete, it is worth considering the features of this material and the differences from more traditional brick, concrete and stone. First of all, this applies to the cellular structure of the blocks, which were originally considered insulation, and only then they began to be used for the construction of the walls themselves. Due to the open structure, which is the result of adding a special blowing agent (aluminum powder) to its composition, aerated concrete has a high level of vapor permeability. This characteristic is one of the main ones when choosing a material and finishing method.

Regardless of the choice of how to plaster aerated concrete, finishing work should start from the inside, and only then deal with the facade of the building. Changing the order and performing first external, and only then internal finishing, leads to too high humidity in the room. Escaping (especially in severe frost) steam condenses in the walls at the border of aerated concrete and finishing. The moisture created during this can lead to the appearance of cracks in the plaster and the falling off of its pieces. That is why the interior finishing work is performed in the first place.

Choice of method and material

When performing finishing work, plastering of aerated concrete walls indoors is performed in one of two main ways. The meaning of the first is not only to preserve, but even to increase the vapor permeability of the blocks. The second, on the contrary, assumes complete vapor barrier. The advantages of maintaining vapor permeability lie in the creation of an optimal microclimate, and the option with insulating the walls - in the safety of the external finish, which is not affected by the steam leaving the building.

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Unsuccessful options

It is not recommended to use cement mortar for plastering aerated concrete inside. The first reason is that smooth blocks do not allow the material to stick. The cement layer quickly falls off and the finishing has to be done again. Secondly, the best option for plastering blocks is considered to be a material with the same or greater vapor permeability index as compared to aerated concrete. For cement, this characteristic is much lower, which does not allow maintaining normal conditions inside the building. For the same reason, the answer to the question of whether it is possible to plaster aerated polystyrene or polystyrene foam concrete will be negative.

In addition, the cement-sand mortar has a high humidity due to the significant amount of water required for its preparation. Aerated concrete structures with a high water absorption rate absorb liquid from the finishing material. The quality of the mortar, which requires uniform drying to cure, decreases, as does its ability to adhere to walls. As a result, cracks appear on the plaster, and its quality decreases, bringing the next repair closer.

You should not choose a special adhesive mixture for finishing aerated concrete inside. Despite the fact that it is designed taking into account the peculiarities of the material, it is advisable to apply the glue in a thin layer, which is not suitable for protection against cracks. As soon as the vapor permeability of the block is broken, they will immediately appear on the surface of the thin-layer plaster for aerated concrete from the adhesive mixture;

• cracks;
• seam marks;
• and even mold.

Breathable finish

Choosing the option of decorating the walls of aerated concrete indoors while maintaining the natural vapor permeability of the material, they use plaster mixes on gypsum and gypsum putty. Due to the slaked lime and perlite sand in their composition, water vapor easily penetrates through the plaster layer. Another advantage of this option is that there is no need to prime the surface of the enclosing structures.

Slightly less often, mixtures containing a high content of such natural materials with a high degree of vapor permeability are used as internal plaster of aerated concrete walls:

• chalk;
• marble;
• dolomite;
• limestone.

Their vapor permeability indicators are higher in comparison not only with internal, but even with external plaster, and the dried solution is easily rubbed off, acquiring ideal whiteness. The resulting coating has excellent durability and allows further finishing.

You should know: Due to the porous structure of concrete, it is recommended to putty it only after applying a primer. If this is not done, cracks will appear on the putty.

Vapor barrier finish

When choosing the finishing of aerated concrete indoors with the elimination of vapor permeability, that is, with complete insulation of the enclosing structures, one of the materials is a polyethylene film. The easiest and fastest way to fix it on the walls is to lay it under one of the finishing layers. However, the speed and ease of installation do not matter if condensation forms on the structures finished in this way and the plaster swells. A more suitable option for plastering aerated concrete inside a house is a sand-cement mixture, which does not contain additives in the form of dolomite flour or lime. With its help, the vapor permeability decreases several times, however, the possibility of plaster peeling increases after a while.

Additionally, to reduce vapor barrier, without too much affecting the quality of the finish, will help:

• oil paint, which covers the walls at the final stage of work;
• applying 3-4 layers of a special composition as a primer for aerated concrete;
• use of adhesives before applying the plaster. In this case, you can even do without using putty. Adhesives have the same properties and, in fact, replace it.

Features of work

To finish the aerated concrete with plaster with your own hands, you need to use the same tools that are needed for ordinary plastering. To prepare a plaster mixture, a special container is needed - such as a plastic tank or a bucket made of the same material. They should be large enough to accommodate all the ingredients for the plaster.

Water is added to the dry mixture that is poured into the tank. The mixture is mixed to the desired state with a drill with a nozzle or a construction mixer. As a rule, it is possible to determine the proportions of material and liquid by the inscriptions on the packaging with building materials.

Plaster of aerated concrete walls is applied inside the room by "throwing" using

such tools as:

• Master OK;
• plastering bucket;
• trowel.

The surface is rubbed with a trowel. And the excess solution from the wall can be removed with a scrubber. It is required to level the wall with the help of beacons, and pulling off the plaster mortar is the rule. Another tool that you cannot do without when performing work is a rail from floor to ceiling length. With its help, defects on the walls are checked - deviations of no more than 6-7 mm in size are considered permissible.

Plastering process

Having decided the question of how to plaster the walls of aerated concrete, they proceed directly to the work. They begin, like all surface finishing methods, with the preparation of the base. The blocks are cleaned of the mixture residues and the seams between them are closed. Before plastering aerated concrete indoors, a layer of primer is applied to the porous surface.

Solutions for aerated concrete blocks, assuming the preservation of vapor permeability, are also

capable of passing steam, differing not only in high hydrophobizing properties, but also in the ability to strengthen the enclosing structures. The primer is required to be applied not in one layer, but in several. In this case, it must be taken into account that a new application is carried out only over a completely dried old one.

Further, the technology of plastering walls from aerated concrete includes such stages as:

1. Anchoring the mesh for block reinforcement. Due to the large size of each aerated concrete product, the value of their adhesion to finishing materials is small. And to increase the strength, reinforcement with a material is used, which contains an alkali-resistant fiber. Can be used for the gas block mesh "chain-link" with a small cell size. For its fastening, the use of 120 mm nails is required, which are well driven into aerated concrete;
2. If reinforcement is not used (it is necessary to decide whether a mesh is needed when plastering aerated concrete at the stage of choosing materials), the adhesion of the finishing layers to aerated concrete is ensured by grooves intersecting each other, performed by any suitable tools - for example, a hacksaw.
3. Application of the first layer of material (pre-selected, the better to plaster aerated concrete) on the mesh. At the same time, the "spraying" technology is used, which ensures the complete filling of the aerated concrete cells, and the leveling of the first layer is not carried out, which improves the adhesion to the next layer of plaster.

When applying the priming solution over the rough aerated concrete plaster, it is required to maintain the layer thickness at the level of 4–5 mm. Adding slag sand to the primer is recommended. When applying the finishing plaster layer, it is advisable to use building material, which contains fine sand, which increases the smoothness of the blocks.

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The final stage

At the penultimate stage of plastering, the surface of the plaster layer is made almost perfectly flat by smoothing the already dried solution. The approximate time after which you can smooth the plaster is 24 hours. In order for the surface to be smoother, the blocks are moistened with water.

The last stage is painting with special paints. For this, materials are chosen that have a high degree of vapor permeability. After painting, it is advisable to apply a water repellent on top of the paint layer, which increases the strength and durability of the finishing layer several times.

The operational life of the resulting interior decoration depends on a number of factors. For example, on the quality of finishing materials, which can be determined by cost (good plaster will not be cheap). Although the characteristics of the aerated concrete itself are of no less importance - even expensive plaster will not adhere well enough to a low-quality surface.

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