Aerated concrete is increasingly used in private construction, competing with traditional bricks. Such houses are much warmer, and less time is required for construction. In terms of technical characteristics, aerated concrete differs markedly from other materials, and these differences must be taken into account when choosing an exterior finish for walls. Plastering is considered the most popular option, and in order for the coating to match the base material as much as possible, you need to choose the right composition.
Facade plaster for aerated concrete
Let's consider in more detail the types of facade plasters for aerated concrete and the correct technology for their application.
Aerated concrete has a cellular structure with open pores, which provides not only thermal insulation properties, but also high vapor permeability. Thanks to this quality, an optimal microclimate is created inside the house, the accumulation of condensate is excluded, and the risk of mold development is minimized.
Aerated concrete walls
Aerated concrete house
But there is also a downside: open pores increase the hygroscopicity of the material, and absorbed water, when frozen, destroys the cells. For this reason, the exterior finish must necessarily be waterproof in order to reliably protect the walls from moisture, and have a vapor permeability not lower than that of aerated concrete, so as not to impede the escape of vapors.
Disadvantages of aerated concrete
Important! According to the standards prescribed in SP 50.
13330. 2012, in heated houses, the vapor permeability of materials should increase from the inner to the outer layers. Only under such conditions is the normal functioning of the supporting structures possible. Since for aerated concrete this parameter varies within the range of 0.11-0.
23 mg / (m · h · Pa), then the plaster composition must be chosen with a vapor permeability of at least 0.12 mg / (m · h · Pa).
In addition, the facade plaster must have the following qualities:
In principle, aerated concrete surfaces can be operated without a protective coating, but after a few years the visual appeal will disappear: the blocks will darken, delamination will appear, and mold may develop. So it is better to immediately complete the facade decoration and then only periodically renew the coating with painting.
Renewal of plaster by painting
The most common and most budgetary plaster for outdoor use is cement-sand. But since its vapor permeability is only 0.09 mg / (m · h · Pa), it is not at all suitable for aerated concrete structures. Other types of plaster mixes, such as mineral, silicate and silicone, have the required parameters.Let's consider the characteristics of each of them in more detail.
Mineral-based plaster belongs to inexpensive materials and is easy to make with your own hands. The main disadvantage is the limited color gamut, but since this coating lends itself well to staining, this is not such a big problem. The ready mixes contain lime, white cement, marble chips and other fillers, as well as some additives that improve the quality of the plaster. Homemade mixes are most often made from cement, lime paste and sand, or only from sand and lime. It is worth noting that sand-lime solutions have low water resistance, and the direct effect of precipitation is destructive for them.
Lime plaster on the wall
High-strength medium-grain exterior (facade) mineral lime-based coating
Decorative plaster Ceresit CT 35
Liquid potassium glass acts as a binder in silicate plaster. Such compositions are more convenient to apply, they are not afraid of moisture and are perfectly permeable to fumes, which allows them to be successfully used for finishing aerated concrete walls as a topcoat.
Silicate plaster - photo
Facade wall, decorated with silicate plaster, will serve you for at least 25 years
The range of colors is rather limited, but, again, this drawback can be easily eliminated by coloring. Silicate plaster goes on sale in a ready-to-use form, and the cost is slightly higher than dry mineral mixtures.
Silicone plaster is based on organic silicon polymers.
It has the best characteristics in comparison with other types of plasters: it does not absorb water, it is easy to apply, it is resistant to atmospheric influences, it is vapor permeable and does not lose its visual appeal for a very long time. In addition, such a coating remains elastic and does not crack when the aerated concrete blocks shrink. Silicone plasters are also sold ready-to-use and come in many color options. Thanks to the presence of special fillers, silicone plasters make it possible to create a variety of coating textures. The only negative is the high price of the material, so not everyone can afford such a finish.
Silicone plaster can be of different fractions
Texture of bark beetle from silicone plaster
But acrylic plasters for aerated concrete can be used only under the condition of enhanced waterproofing on the inside of the walls and high-quality ventilation of the premises. This is due to the low steam permeability of the material, which is closer to cement-sand compositions.If you do not provide sufficient protection for the internal surfaces, water vapor will begin to accumulate in the thickness of the walls and provoke the peeling of the finishing layer.
Facade decoration with acrylic plaster
Ceresit CT 24
| Dry mix on a mineral basis. Differs in plasticity and ease of application. |
The finished solution must be used within an hour. Application thickness - from 3 to 30 mm. After drying, the coating can withstand temperatures from -50 to + 70 ° C, and at least 100 freezing cycles. Dry mix consumption per m2 is about 14 kg when applied 10 mm thick. The coating can be painted 7 days after application
Osnovit Startwell T-21
| Cement-lime dry mix. |
It has good resistance to shrinkage, firmly adheres to the base, and is not afraid of moisture. It is applied with a thickness of 5 to 30 cm, consumption is 14 kg with a layer thickness of 10 mm. The ready-made solution should be used within 3 hours. Frost resistance of the coating is equal to 50 cycles, can be operated in the temperature range from -50 ° C to + 65 ° C
| Ready mix based on silicone resins. Very flexible, firmly adheres to the base, forms a strong coating with dirt and water repellency. |
The palette includes about 200 colors and shades. Consumption is 2.5-3.9 kg / m2, depending on the thickness of the application
Weber. pas silikon
| Plaster based on silicone emulsion, ready to use. |
It has a different grain size - from 1.5 to 3 mm, tinted in more than 200 colors and shades. The coating is resistant to moisture. Pollution, exposure to ultraviolet radiation and temperature extremes. Consumption is 2.
4-4.7 kg / m2
| Ready-to-use silicate plaster. Has a grain size of 1.5 to 3 mm and 200 tinting options. Forms a dense coating with high vapor permeability and moisture resistance. |
Approximate consumption 2.5-4.2 kg / m2
CERESIT CT 77
| Acrylic compound with mineral filler. It can be used for exterior finishing of aerated concrete blocks in the presence of internal water protection and ventilation of premises. Forms a thin but durable coating that is resistant to negative effects. |
Possesses frost resistance up to 100 cycles, consumption is 4.5-5.2 kg / m2
Ceresit CT 77 color palette
Plastering aerated concrete facade is possible only after all the "wet" processes inside the room have been completed and the surfaces are completely dry. This applies not only to plastered and painted walls, but also screed on the floor, from which moisture evaporates very actively. The blocks themselves must also be dry - the maximum allowable humidity is 27%.
If plastering on wet walls, the intense release of water vapor will cause the coating to flake off.
The walls of the house must be dry
It is recommended to perform plastering of the outer walls at a temperature of + 5 ... + 30 ° C, while the relative air humidity should not exceed 80%.
If for some reason it is not possible to finish the exterior before the onset of frost, you need to treat the entire area with a deep penetration primer. The best option is the Ceresit ST-17 primer, applied in 2 layers. Such protection will be enough until spring, when weather conditions will allow you to start plastering.
Ceresit CT 17. Deep penetration primer
Do not apply plastering compounds in heat, in strong winds and under the influence of direct sunlight on the walls. These factors contribute to the rapid drying of the solution, and it does not have time to firmly adhere to the base. As a result - the appearance of many small cracks and plaster flaking.
Deep Penetration Primer
As a rule, the walls made of aerated concrete blocks are quite even and smooth, so there is no need to specifically level them. If there are deep chips or dents, you need to seal them with the glue that was used when laying the blocks.
Glue for aerated concrete
To do this, knead a little glue (you can mix it with the dust formed when cutting blocks), collect it narrow spatula and fill in the recesses. Remove excess and allow the solution to dry. The empty seams between the blocks are closed in the same way. When the glue dries, the walls need to be rubbed to remove minor flaws. Use a metal flat grater for this.
In conclusion, dust is swept away from the entire surface with a brush.
Seal all cracks and dents with a mortar
For priming aerated concrete walls deep penetration compounds with strengthening properties are used under the plaster. They create a very strong elastic film that allows water vapor to pass through, but prevents the material from absorbing water. In addition, these primers increase the adhesion of the substrate and the finishing layer.Popular media: Knauf Grundiermittel, Siltek E-110, Aerated concrete-contact-1.
Gas concrete contact-1
The primer is applied in 1-3 layers, depending on the climatic conditions of the area. For example, in dry and warm regions, one layer of primer is enough, and in areas with a damp climate, coastal areas, three layers are needed. To apply the composition, use a roller or a wide paint brush. They are primed with a continuous layer, evenly distributing the composition over the base. In corners and hard-to-reach places, a narrow brush is used so that no dry areas remain.
Wall priming tool kit
Walls can be primed with a roller
It is not necessary to reinforce a layer of plaster up to 10 mm thick if the walls are properly primed. With a greater thickness, reinforcement is indispensable, and for this, a fiberglass mesh with a mesh size of 3x3 mm is used. The mesh must be alkali-resistant - this will ensure high durability and strength of the finishing layer. This information is indicated on the packaging, so when buying a mesh, pay attention to this item.
Prepare plaster mortar. The proportions of water and dry mixture are in the manufacturer's instructions, so carefully read it before starting work. For mixing, take a clean container, pour the specified volume of water with a temperature of + 15 ...
+ 20 ° C. Pour in dry components and stir with a construction mixer at a speed of 400-800 rpm. Let the solution brew for 5-7 minutes and stir again.
The solution is best prepared in small portions
How to prepare the plaster mortar
Step 2. Take a wide metal spatula , apply a solution to the edge and apply an even strip to the wall.
The spatula must be held at an angle to the surface and not pressed too hard, so the composition is distributed most evenly. The layer thickness should not exceed 5 mm.
Distribute the mixture along the wall
Step 3. A grid is placed on top of the solution, straighten it, and then gently deepen into the plaster, rubbing with a spatula over the surface with effort. If necessary, add the solution in small portions and grind well again.
After fixing the mesh, apply the solution to the next section and repeat it all over again. The mesh must be laid with an overlap of 40-50 mm to avoid cracks at the border of adjacent areas.
We attach the mesh
Step 4. In the corners, special perforated profiles are attached with a mesh fixed at the edges. To do this, apply the solution to the very corner, level it with a spatula, apply an angular profile and gently press it.
Then, like the mesh, it is deepened into the plaster and the surface is leveled with a spatula.They are placed not only in the outer and inner corners, but also along the perimeter of window and door openings.
Corners and mesh should not protrude above the plane of the wall anywhere. The surface must be flat, smooth, free of visible defects. Now you need to let the solution dry well.
Drying time depends on the composition of the mixture and weather conditions, on average it ranges from 3 to 7 days.
Mix the finishing layer solution and apply with a wide spatula onto the surface. The thickness of this layer varies between 4-10 mm. Special care is required here, since all defects will remain in sight. When plastering adjacent squares, the formation of stripes at the edges should be avoided, all excess must be immediately removed with a spatula.
Plastering on aerated concrete walls
When the plaster has set enough, but has not yet completely hardened, proceed to grouting the walls. For this, it is most convenient to use a polyurethane float, but a metal float is also suitable. The grater must be applied flat to the surface, pressed down, and smooth the plaster layer in a circular motion. Do not press too hard so as not to leave scratches and dents.
After grouting, it is necessary to wait until the plaster is completely dry, and only then proceed to the final stage - painting.
You can also apply decorative structural plaster by applying a thin layer to the prepared substrate.
After plastering, decor can be attached
Posted By: Work Style |04, Nov 2020
Posted By: Work Style |01, Nov 2020
Posted By: Work Style |01, Nov 2020
Posted By: Work Style |02, Nov 2020
Posted By: Work Style |02, Nov 2020