Plastering aerated concrete: what you need to know for successful implementation

Working with aerated concrete for plastering can differ slightly from other wall materials. Because of its porous nature, plaster application requires extra care even though it’s great for insulation. An improper application could result in a finish that breaks easily or even detaches.

A durable and smooth plaster finish on aerated concrete requires knowledge of the proper methods and supplies. Every stage of the project, from selecting the right primer to applying the finishing coat, is vital to its success.

This post will walk you through the essential elements to guarantee that the plastering job you do on walls made of aerated concrete is done correctly the first time.

Aerated concrete has special qualities that must be carefully considered when plastering. Because of its porous structure, a long-lasting finish can only be achieved by carefully selecting the plaster mix and performing surface preparation. You can achieve a smooth and long-lasting plastered surface that improves the look and functionality of aerated concrete walls by being aware of these crucial elements.

Features of aerated concrete

You must research the characteristics of aerated concrete blocks in order to determine the best mixtures to use for plastering walls. The production technology is to blame for them. Porous artificial stone can be made in two ways: by autoclaving or by natural hardening (hydration or non-autoclave).

The variations are as follows:

• color (hydration – pronounced gray);
• geometrical accuracy (autoclaved is more accurate);
• strength (autoclaved has higher indicators);
• density, thermal conductivity (autoclaved has the optimal ratio of indicators);
• brittleness (hydration is in the lead);
• durability (autoclaved is in the lead).

Lime, quartz sand, cement, water, and a gas-forming reagent (typically an aluminum powder or paste) are combined to make aerated concrete. Lime and aluminum react when the mixture is mixed, releasing hydrogen. As the gas is released throughout the volume, many tiny pores are formed. Additionally, gaps appear between the pores because light hydrogen tends to escape.

As a result, air channels flow through the tiny pores that dot the aerated concrete structure. The material stands out for their increased permeability to vapor and water.

The following are the drawbacks of the porous material, regardless of how it was made:

• high water absorption;
• ability to cause corrosion of metal fasteners;
• poor adhesion;
• unaesthetic appearance;
• blowability (through channels that retain heat in calm weather lose their thermal insulation properties in windy weather);
• rapid destruction in the absence of a protective finish.

As a result, aerated concrete in particular needs to be covered with appropriate materials.

The protective techniques employed:

• ventilated facade (granite tiles, clapboard, siding, etc.);
• "wet facade";
• protective coloring;
• brick cladding;
• plastering.

You should be aware of the superiority of each of the current finishing materials when selecting plaster protection.

Basic requirements for plaster

A healthy microclimate should be facilitated by the compositions used indoors for the protective plastering of aerated concrete walls. Aerated concrete facade plaster should also be water- and weather-resistant, with low water permeability and the capacity to tolerate temperature swings.

Regardless of the application location, the aerated concrete plaster needs to possess the following qualities:

• reliable adhesion to the aerated concrete surface (≥0.5 MPa);
• vapor permeability;
• strength;
• water requirement of no more than 200 ml per 1 kg of SS (dry mix);
• fire resistance;
• environmental friendliness;
• biostability;
• durability;
• decorativeness.

What plaster is best for plastering aerated concrete walls

Plaster compositions designed especially for aerated concrete blocks have been developed with the aforementioned requirements in mind.

• mixtures for interior work;
• general-purpose compositions;
• facade plaster.

Since aerated concrete plaster is used in the most adverse conditions, it is the most durable of the specified compositions for exterior work.

The compositions’ objectives are:

• regular (for leveling – rough finishing);
• special (perform additional functions, such as insulation, wall sanitation, waterproofing, etc.).d.);
• decorative.

By kind of base for binder:

Information regarding the solution’s shelf life is crucial for novices. Plastering must be done quickly because the solution takes a short time to set.

Silicate plaster

Silicate plaster is bound together with liquid glass. This material is strong and has the following benefits:

• vapor permeability;
• durability;
• resistance to aggressive substances of a gassed atmosphere;
• strength;
• resistance to biological damage;
• resistance to long-term exposure to UV radiation;
• fire safety;
• strong adhesion to the base;
• no shrinkage during hardening;
• easy cleaning (dirt is washed off by rain or watering from a hose).

Porous and "soft" materials are perfectly protected by silicate coating.

• it requires primers (as well as paints and varnishes) on a related basis;
• this product is not cheap;
• poor range of ready-made mixtures;
• requires work skills, since the shelf life is limited (presents a problem for beginners);
• under the influence of precipitation, the coating darkens, becomes spotty for a while;
• work clothes are not cleaned after plastering.

Seldom used to decorate interior spaces. They create dry, pre-made mixtures.

Silicone plaster

Silicone, a relatively new binder, works well in plaster compositions when it takes the form of silicone resins. The expensive price is the only real downside.

• vapor-permeable;
• very strong;
• durable;
• highly elastic (cracks do not form even when cracks form in the walls);
• firmly adhering to any surface (except for metal bases);
• resistant to chemicals;
• not affected by bioorganisms;
• preserving strength and appearance at high temperatures;
• with unlimited layer thickness;
• does not collect static;
• easy to wash;
• hydrophobic.

Applications that are universal.

Acrylic plaster of aerated concrete

Has become more well-liked as a result of an alluring value and quality combination. developed using acrylic resins, which are derivatives of acrylic.

• elastic;
• strong;
• ecologically friendly;
• waterproof;
• easy to lay;
• durable;
• has a rich palette;
• is not susceptible to damage by fungi, rot, mold;
• washable with a hose.

• accumulates static;
• low vapor permeability;
• not resistant to flame;

Additives are employed in order to offset the drawbacks. Nevertheless, living rooms and bedrooms do not use these mixtures.

Cement-sand

We instantly dismiss the notion of utilizing traditional cement compositions. For example, standard sand-cement mixtures (CPM) are too heavy and dense for brittle aerated concrete; as a result, surface cracks are unavoidable due to low adhesion.

The primary cause of cement-sand mortar’s inability to be plastered over is its lower vapor permeability than that of cellular concrete. It gets hard to create the ideal microclimate for habitation.

With the aid of additives, top companies have altered the cement mixture to make cement-sand mortar appropriate for porous bases.

Lime-cement

Lime is added to cement compositions to overcome low vapor permeability and poor adhesion to aerated concrete. You can prepare these compositions yourself, which will save money.

• high vapor permeability;
• plasticity (easiness to place);
• strength;
• environmental friendliness;
• ability to maintain a microclimate favorable for health;
• good adhesion;
• bactericidal properties;
• fire resistance;
• cheapness.

• the coating does not withstand vibrations;

Gypsum

The most popular mineral composition for interior plastering is aerated concrete plaster with a gypsum base.

• hardens quickly, gaining strength;
• non -shaped, when solidify, cracks do not appear;
• It has vapor permeability;
• plastic, easily fits, holds the applied shape;
• firmly adheres to aerated concrete;
• does not give his water to a porous base;
• environmentally friendly;
• fireproof;
• forms coatings with low weight;
• repairs;
• lightly grinds;
• capable of forming a smooth surface.

• "rabies";
• low frost resistance;
• Small life life.

This composition works the best for plastering residential buildings’ aerated concrete surfaces out of all of them. Aerated concrete walls and partitions typically have a smooth surface, so plastering can be done with the least amount of thickness. This is 1 mm for mixtures of gypsum. For cement solutions, the answer is 10 mm.

The most popular manufacturers

All of the major plastering manufacturers have plaster mixtures available for finishing aerated concrete. Combinations of well-known brands can be identified by how closely the attributes match the stated indicators.

The following businesses are well-known manufacturers:

• German concern Henkel (develops and produces plasters under the Ceresit brand);
• Austrian brand Baumit;
• Knauf company, which initially produced gypsum mixtures, also produces cement-based mixtures;
• Krasland company;
• Bolars (Uniplast mixture);
• A number of plasters for aerated concrete are produced by the Pobedit company.

The most popular brands of aerated concrete from the Ceresit line are CT 24 and CT 77, among others. CT 24 is a lightweight, frost-resistant, vapor-permeable plaster mixture for general use that is based on cement. For aerated concrete, CT 77 is an acrylic facade plaster, and CT 35 is a decorative mixture for use as "bark beetle" on facades.

Popular cement-lime composition Baumit HandPutz for all-purpose use, silicone composition in the Baumit line Mixture of silicates, SilikonTop SilikatTop, Nanopor acrylic top.

Knauf mixes like gypsum Knauf-Profi, gypsum polymer Eisberg, and gypsum with polymer additives are appropriate for aerated concrete walls. Cement Grunband (thermal insulation), Rotband, Goldband, and Sevener.

Aerated Concrete-2 is one of the compositions made especially for aerated concrete walls by the Krasland company.

Plastering features

Upon production, aerated concrete blocks are transported straight to the building site, where they retain up to 30% of their unweathered moisture content. Water seeps into the blocks during installation from precipitation and the masonry mortar. As a result, moisture is trapped within a newly constructed building’s walls. They must remain under the roof for at least six months in order to dry out. In the first year, aerated concrete shrinks as well.

New construction is not plastered as a result. Additionally, because the walls need time to dry, it is impossible to plaster aerated concrete both inside and outside the house at the same time.

General layout of a plastered wall "pie" with multiple layers: the exterior coatings are the most vapor-permeable, while the interior coatings are the least.

In moist climates, plaster now rather than waiting for the next season. High vapor permeability, highly plastic compositions are employed.

The external plaster coating should have a higher vapor permeability than the interior finish.

How and what to plaster aerated concrete inside the house

Given the greater variety of mixtures available, choosing a composition for internal plastering of aerated concrete walls is less complicated than external plastering. Mixtures are appropriate for external work in addition to interior plastering. Furthermore, gypsum compositions can be used indoors. It is recommended to use compositions whose vapor permeability is less than that of aerated concrete. Denser compositions or waterproofing mixtures are used in damp rooms.

There are certain choice-related issues. They appear if foam plastic or expanded polystyrene was used as facade insulation (without a ventilation gap). Since moisture cannot be removed from aerated concrete walls and enter the room, these materials are essentially vapor-impermeable. See our articles for more information about plastering foam plastic or expanded polystyrene.

Plaster compositions with vapor permeability significantly lower than that of aerated concrete blocks inside the room are used to block access to aerated concrete because moisture builds up inside the wall. That is, thick plaster made of cement. In this instance, the ventilation system plays a bigger part in clearing the space of moist air.

For facades, silicate, cement-lime, and silicone mixtures are appropriate; for rooms, gypsum-lime, cement-lime, and gypsum-perlite compositions are appropriate.

If plastering inside is done first, steps are taken to prepare the base, which has very low adhesion and can readily and extensively absorb water, in addition to selecting plasters that work well with aerated concrete. Deep penetration primers must be applied to the walls in accordance with the manufacturer’s instructions. Even tiny excesses of water in the primer and plaster compositions are prohibited.

When plastering aerated concrete walls indoors, a rough plaster layer (at least 0.5 cm) is applied, and fiberglass or polyurethane reinforcement is used to address low adhesion.

How and what to plaster aerated concrete outside the house

They use the guideline that the vapor permeability of the external material should be at least as high as that of the aerated concrete when determining how best to plaster aerated concrete outside. The compositions have to be universal or meant for facades. The loads and impacts on the surface of the structure are greater outside the house. As a result, reinforcement is essential.

It is preferable to use plasterboard, mineral wool, or heat-insulating plaster for exterior insulation.

It is coated with a water-repellent compound a year after the finishing layer is applied, giving the surface water-repellent qualities.

Optimal conditions for applying plaster

In order to achieve the desired qualities in a plaster coating, a number of requirements must be met, including the circumstances surrounding plastering. The temperature range for plastering aerated concrete walls during interior work is +5 to +30 °C. The room is not permitted to have drafts or humidity levels above 60%. Timing the start of plastering to coincide with the end of the heating season makes more sense.

Select a period of time when the temperature stays at least +8 °C for several days when plastering externally on aerated concrete. When there is more than 80% humidity, a chance of frost, wind, or extreme heat, do not plaster the facade. The area where the work is finished is shielded from the sun and rain.

In the event that plastering the facade is not feasible before the season ends, it is primed twice using a deep penetrating agent and left until spring. In addition, a film covering is occasionally applied to the walls for the winter.

Technology of plastering aerated concrete facades

What is the best way to plaster aerated concrete block walls?

For aerated concrete walls and partitions, there are two ways to apply solutions:

• thick-layer (the solution is applied in one layer, then rubbed);
• thin-layer (the mixture is applied in several passes).

Here is a general, step-by-step breakdown of plastering:

1. Prepare the base.
2. Apply a primer.
3. Prepare the solution or prepare a ready-made mixture.
4. Apply the first layer, reinforce, process with a notched trowel, dry.
5. Apply the second layer, leveling the comb of the first. Dry.
6. Apply the third (smoothing) layer. Rubbed. Dry. Sand. A layer is performed if it is necessary for finishing, for example, painting.

Surface preparation

A fairly even masonry can be created by builders thanks to the accuracy with which aerated concrete blocks are manufactured. Such walls need to be prepared in advance. The blocks are typically placed on an adhesive substance. In this instance, the walls dry faster and the blocks do not become as damp as they would if they were laid on mortar.

If the adhesive solution extends beyond the wall’s plane during preparation, it is planed using a plane or a float made for aerated concrete. Some protrusions can also be chopped off. If there are any chips or cracks, they are filled with an adhesive mixture, to which dust created when cutting blocks is added. Using a narrow spatula, fill the depressions, remove any excess, and allow the adhesive composition to dry. The surface is then rubbed after this.

Sweeping away the dust completes the aerated concrete’s plastering preparation.

Priming

A brief discussion of primers for aerated concrete prior to plastering.

The most widely used formulations are Siltek E-110, Aerated Concrete-Contact-1, and Knauf Grundiermittel, which penetrate deeply. Aerated concrete blocks with an acrylic siloxane primer have a water-repellent surface. Using a roller or brush, apply a layer of primer in two or three passes, then let it dry. A single layer may be adequate in arid regions; three layers are needed in humid regions.

Aerated concrete plaster and reinforcement

What questions beginners have are: do they need a grid? Reinforcement is not necessary if the solution is applied in a single layer up to 10 mm in the presence of a premium primer in the space. On the other hand, the mesh is an extra strength that is necessary for the facade coating.

Using a spatula, add fiberglass mesh (stable to alkalis!) with 3 x 3 mm cells to a newly laid layer of the solution (at least 5 mm) and feed it in. There is a 5 cm gap between the panels. Using a notched trowel, a layer with mesh is created, resulting in horizontal stripes and ribs, and is then dried.

Beacons are used if the coating thickness is ≥7 mm. Apply two additional layers when working outside: one for leveling, and another for creating a sturdy, even surface. The latter, wiped with abrasive nets or sandpaper.

The finish layer

Wallpaper, paint, and plaster are the most common decorative materials used on walls. Vapor permeability should be present in these materials. Prior to applying the finish, the dried plaster coating’s surface is primed. The section on decorative plaster presents wall plaster technology with decorative compositions.

Aspect	Key Information
Surface Preparation	Ensure the aerated concrete is clean, dry, and free of dust. Use a primer to improve plaster adhesion.
Plaster Choice	Select a plaster specifically designed for aerated concrete, such as lightweight or breathable options.
Application Technique	Apply the plaster in thin layers, allowing each to dry before adding the next to prevent cracks.
Drying Time	Aerated concrete absorbs moisture quickly, so allow adequate drying time between layers.
Finishing	Use a float to smooth the surface after the final layer, ensuring an even finish.

Paying close attention to detail and having a thorough understanding of the special qualities of aerated concrete are essential for successful plastering. Because of the high absorption capacity of this kind of concrete, adequate surface preparation is essential to ensuring long-lasting and excellent plaster adhesion.

Making the proper plaster mix choice is also crucial. It’s critical to choose a plaster that will both provide a smooth and long-lasting finish and allow the aerated concrete to breathe. Correct application of the plaster in thin, even layers will help prevent common problems like peeling and cracking.

These instructions will help you achieve a high-quality, long-lasting plastered surface on aerated concrete that looks fantastic. The success of your project will be entirely dependent on careful planning and execution.

Video on the topic

Why do we not cover the seams in aerated concrete?

Plaster-spacecoma of aerated concrete.

A house of aerated concrete cracked . Why aerated concrete crack ? Answer in comments

Cement-sand plaster, part 1 theory

How to plaster a gas block?! | Cement or gypsum plaster?!

Such plaster in aerated concrete will never fall off!

How to plaster aerated concrete, preparation of the base of the block