Is it necessary and how to plaster aerated concrete blocks indoors

Because they are lightweight and have excellent insulation qualities, aerated concrete blocks are becoming a common material for building homes and other structures. But a lot of builders and homeowners question whether plastering these blocks inside is really necessary. Plastering can require a large time and financial commitment, so this question comes up frequently.

Plastering not only makes walls look better, but it also creates a smooth surface that is simple to decorate or paint. It can also increase the interior walls’ general durability and shield the blocks from moisture. However, is it always necessary, or are there instances in which you can omit this step?

This post will discuss the pros and cons of plastering aerated concrete walls as well as situations in which leaving them unpainted may be acceptable. Acquiring knowledge about the advantages and possible drawbacks of plastering can assist you in making an informed choice, regardless of whether you intend to undertake the work yourself or hire experts.

Features of aerated concrete

In order to identify the tasks, the appropriate choice of plaster composition, and the technology, it is necessary to study the primary characteristics and properties of the material before plastering a house made of aerated concrete, either inside or outside the premises. Similar to foam concrete but with a different structure, aerated concrete is a kind of cellular lightweight concrete.

In the process of making aerated concrete, special additives—typically aluminum powder—are added to the concrete mixture to create foam and increase the number of pores.

Gas bubbles escape into the concrete mixture during the hardening process, resulting in an open, finely porous structure. It turns out that there are a lot of thin channels that penetrate the gas block, and these channels have a tendency to absorb moisture.

The number of air pores within a block determines its density, which in turn influences the mechanical strength, thermal insulation properties, and range of applications for aerated concrete. Blocks with higher strength and density but lower thermal insulation qualities (fewer pores in the structure) are used for load-bearing walls and internal partitions. Low-density, low-strength blocks with lots of air pores are used for thermal insulation.

The following table lists the attributes of the most well-known aerated concrete brands:

• The material is lightweight, as the density and weight increase, the strength increases, but the insulating properties decrease. Nevertheless, the thermal insulation properties of aerated concrete are high, regardless of the brand (if compared with other materials).
• Aerated concrete is hygroscopic, vapor-permeable, therefore it requires mandatory protection from moisture both inside and outside. Otherwise, the material quickly absorbs water, which, when frozen, destroys it (first cracks appear, then deformations and complete destruction).
• Aerated concrete blocks are characterized by low mechanical strength (even with the highest density), therefore they do not tolerate accentuated impact, which causes cracks to spread and chips to appear.

• The porous structure of concrete easily passes air flows, therefore, without finishing the external walls and partitions, the building will simply be blown through.
• Gas blocks are not very aesthetic – if a house made of natural wood or red, white brick can be left without finishing and it will look good, then aerated concrete requires mandatory decorative finishing.

Facades of aerated concrete blocks are frequently finished with curtain systems to preserve and beautify the walls. Plastering the walls and painting or finishing them with other kinds of appropriate materials is also relevant.

Gas block compositions are chosen specifically, adjusted to operating conditions, and able to carry out all tasks assigned to them. Additionally, installing an extra layer of thermal insulation is necessary in some areas when using aerated concrete.

Dependence of the technology of plastering from the inside on the external finishing of the facade

Aerated concrete blocks must be used to complete the structure while taking into account the properties of the material and going in the right order. The vapor permeability index must be considered, as external and internal finishing are interdependent. It is preferable to abide by the following guideline: Materials have a higher degree of vapor permeability from the inside out.

Aerated concrete has a high vapor permeability, which can cause condensation to form. The actions of people living in the house, such as breathing, cooking, boiling water, drying and washing clothes, bathing or showering, wet cleaning, etc., cause a significant amount of water vapor to appear.

Although some moisture escapes through ventilation systems, most of it tries to escape through the outer walls during the winter months when windows and doors are closed and the pressure of saturated vapors inside the room can be higher than that of the outside.

Additionally, vapors can freely exit the building if the wall’s structure is properly designed. In other words, materials should have a higher vapor permeability in the direction of the street. Steam escapes through an unfinished wall in this way (though this isn’t a viable option because aerated concrete needs to be protected from moisture):

Through a brick-faced facade with vents and a ventilated gap that permit natural air circulation, steam can escape as follows:

Plaster with a vapor permeability index equal to or less than that of the gas block may be used to finish the interior of the wall. This requirement is met by the majority of putties, or plasters for interior work (on a gypsum base, for example).

In order to prevent moisture from becoming trapped inside the wall, specific compounds used for the exterior finish must be vapor-permeable. A material with good vapor permeability is also chosen in the event that the gas block needs extra insulation; typically, this is mineral wool and other materials of a similar nature.

Steam passes poorly and condensation builds up on the wall when the external decoration is composed of materials with low vapor permissive ability, without a ventilation gap, and with insulation from non-permitting steam materials. Finishing work both inside and outside is planned ahead of time, every detail is well considered, and the indicators are computed to prevent this.

There is only one option if the external finishing is already composed of materials with low vapor permeability: build an internal barrier that can actively thwart steam seeping into the wall. Special hydrophobic compounds are applied to the surfaces, and the work involves the use of vinyl wallpaper, thick plasters made of cement and sand, and specialty paints. In this situation, maintaining a strong ventilation system is crucial to preventing moisture buildup inside, on window glass, and at the corners of slopes.

After 6-7 months from the time the house’s construction is completed, finishing work can be done because, in the absence of such time, the aerated concrete will shrink and the entire finish may develop a network of cracks. Furthermore, the exterior finishing must be completed before the interior.

After all, priming and other wet procedures are used during interior work, and moisture must be allowed to exit the structure. Once the work is finished and the internal humidity level has stabilized, move on to the external finishing.

How and what to plaster an aerated concrete wall from the inside of the premises

Plastering an aerated concrete surface follows a similar technique to that of working with any other material. However, there are some subtleties that need to be considered.

• Due to the open porous structure, aerated concrete cannot be simply covered with putty – a thin layer will not stay on the surface. Therefore, even ideal flat walls need to be plastered with a layer of at least 5 millimeters.
• Without reinforcing with a reinforcing mesh, the layer can become covered with cracks, so it is imperative to use a mesh. It is better to choose fiberglass, resistant to an alkaline environment.
• Aerated concrete has high water absorption, taking moisture from any applied solution, which is why it dries quickly, becomes covered with cracks, crumbles. This happens with the gypsum composition when the normal hydration of cement is disturbed. Therefore, it is desirable to use special plaster mixtures designed to work with aerated concrete.

• It is advisable to use special primer penetration primers.
• It’s not worth giving a thick sketch right away – it is better to apply a minimum layer first, drown a fiberglass grid in it, after drying the main plaster layer along the beacons.

1. Special plastering compositions based on gypsum with light perlite sand in the composition. The instructions should indicate that the composition is suitable for aerated concrete. Example: “Esnovit – Gypswell”, “Plaster”.
2. Plaster based on liquid glass – finishing limits the choice of finishing coating, since silicate mixtures are not compatible with other decorative compositions based on organic type (latex, silicone, acrylic, etc.).d.).
3. Cement-lime based mixtures – optimized for aerated concrete, do not require priming. Example: "AeroStone" and "Baumit HandPutz". Plasters are made on the basis of cement, construction lime, plasticizing additives, special lightweight fillers, purified fine-grained sand. The coating allows steam to pass through well, suitable for internal/external work.

The majority of finishing materials with low vapor permeability are cement-sand plasters that have plasticizers added to them to increase adhesion, but do not contain lime or dolomite chips. Since most specialty mixes for aerated concrete are highly costly, many artisans explore the possibility of using do-it-yourself plaster solutions, which frequently results in issues.

The only way to save finishing costs is to prepare aerated concrete walls for plastering as instructed. Once this is done, practically any mixture can be applied without worrying about over-wetting, drying out, the solution slipping, cracks spreading, etc.

Aerated concrete block plastering indoors may be a sensible option based on your objectives and the layout of your room. It provides a polished, seamless appearance that can improve the visual appeal of your interior. Plaster also serves as an extra layer of insulation, assisting in temperature regulation and enhancing energy efficiency.

But it’s crucial to think about the kind of plaster you use. For example, gypsum plaster is frequently used due to its smooth finish and ease of application, but it might not be the best choice in moist areas. Although cement-based plasters are more resilient to moisture and more durable, they can be more difficult to work with and may need to be applied evenly by a skilled hand.

Plastering aerated concrete blocks should ultimately be determined by considering the unique requirements of your area, such as moisture content and desired aesthetics. Plastering can give an interior a more polished and insulated look, but before beginning the project, it’s important to consider the advantages and disadvantages. Plaster can add both beauty and functionality to your home, making it a worthwhile investment with the right materials and application.

Aerated concrete block plastering is crucial indoors for multiple reasons: it makes the space look better, is more durable, and offers a level, smooth surface suitable for wall coverings or paint. Despite its reputation for being lightweight and having good thermal insulation, aerated concrete can absorb moisture easily and can be porous. Plastering correctly contributes to surface sealing, preventing damage and preserving a cozy interior atmosphere. For homeowners who want to finish their walls, this is an easy do-it-yourself project that only needs basic tools and supplies.

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