- Consideration of specific material properties
- How to prepare the walls
- What mixtures to use
- Preparation for plastering
- Plastering technique
The gas block is one of the most popular masonry materials, which has a number of features related to preparation for decoration. will tell you how to properly cover gas silicate walls with cement and gypsum plaster, to ensure a long service life and crack resistance.
Consideration of specific material properties
Unlike conventional brickwork, aerated concrete has almost zero deformability. There are no thick semi-plastic seams in it, due to which the wall can perceive subsidence of the base without cracking. Seamless or thin-seam gas silicate masonry behaves almost like a monolithic body, and therefore the wall can be covered with a fairly thin layer of hard, albeit fragile, plaster. There is only one condition – ensuring high stability of the structure due to a solid foundation, seismic belt, flexible connections at the abutments of the walls and lintels above the openings.
The second characteristic feature of aerated concrete is its relatively high gas permeability. When choosing a material, it is imperative to take into account such a parameter as the final gas transmission capacity. Indoors, it should be larger than that of gas silicate, thus the interior rough finish serves as a vapor barrier. For external (facade) plaster, the requirement is exactly the opposite – the coating must freely let water vapor into the external environment so that the wall remains dry from the inside.
Ensuring a normal moisture accumulation regime for aerated concrete is especially important. The fact is that during storage and construction of the box, aerated concrete gains a lot of atmospheric moisture. Even if all the requirements for the vapor transmission capacity of the coatings on both sides are met, the removal of excess moisture will take a lot of time. Therefore, the interior decoration of the walls must be performed first and only after that proceed to pouring the floor screed and other wet works. Exterior decoration is done only after the house is completely finished from the inside and warmed up to reduce the humidity of the walls. The moisture content in aerated concrete has an extremely negative effect on the heat-saving characteristics, besides, the walls lose a lot in fire resistance.
Another feature of aerated concrete walls is their relatively low adhesion. Despite the roughness, plaster compounds on a water-soluble binder do not adhere well to aerated concrete. The reason for this is the dust generated during the cutting of blocks and clogging the open pores. Therefore, neither cement nor gypsum plaster can be applied to the wall “as is”; preparation is required.
How to prepare the walls
Before starting work, make sure that all the seams of the gas silicate masonry are filled and not rubbed. The seam material should not protrude on the surface, otherwise the adhesion will be uneven, which can cause cracking and peeling of the coating. It is necessary to carefully inspect the entire surface on which the plaster will be applied, and make sure that there are no greasy streaks or traces of building materials. To reduce the consumption of chemicals, it is recommended to additionally remove dust from the pores using a vacuum cleaner or compressed air.
The main problem of plastering gas silicate walls is that you have to work with a perfectly flat and smooth surface. The retention of the plaster on the surface of aerated concrete is provided mainly not by mechanical, but by electrostatic forces, since the binder hardly penetrates the pores of the material. Therefore, you should first treat the walls with an acrylic primer for poorly absorbent surfaces. Optimal compositions include coarse stone flour – this will strengthen the contact zone and increase the adhesion of the layers to each other.
What mixtures to use
For rough finishing of gas silicate, light thin-layer plasters are used. The material consumption is very low, but its special properties lead to a higher cost. The composition of the plaster mixture includes polymer binders – as a rule, acrylates and air-entraining agents. Special plaster has a large number of micropores and improves the thermal insulation properties.
Standard mixes based on cement and gypsum binder can also be used, but only indoors. Under them, you need to prime the surface more thoroughly, marking areas on the wet track where the liquid is absorbed unevenly, and re-prepare them. The cement plaster mixture also needs modification – the addition of a superplasticizer.
The compatibility of the plaster mixture with aerated concrete is also determined by the operating conditions. In dry rooms, lime and gypsum compositions can be used, in wet rooms – on a cement base. Unlike interior decoration, the facade is performed in two layers: first, the base reinforcing is applied, and then the finishing one, which ensures the final leveling and protection of the base.
Preparation for plastering
If during the erection of the masonry there was no geodetic support and for leveling it is necessary to apply a layer of more than 10 mm, it is recommended to install beacons on the wall. An exception is plaster applied by a machine method and only if the operator is sufficiently qualified..
The installation of beacons is carried out on lumps of solution, the composition of which is identical to the main plaster coating. To facilitate the alignment of the beacons and accelerate the setting, hardening accelerators can be added in small quantities to the mixture:
- for example, stucco – up to 5% by weight of dry components;
- potash – up to 7%;
- sodium carbonate (soda) – up to 0.5%;
- proprietary hardening accelerators based on calcium and sodium chloride in the amount specified in the instructions.
After installing the beacons and forming the base planes, perforated plaster corners should be installed on all edges. In this case, the same composition is used as for fastening beacons.
When the mixture is delivered in dry form, it should be mixed with water, in the ratio indicated in the instructions, and then mixed until smooth with a mixer. Both cement and gypsum mixtures require infusion from 3 to 10 minutes, after which they should be mixed again.
Internal plaster can be applied both manually and by machine. Provided that the surface is properly prepared, there are no problems with fixing the composition on the wall, you just need to “pull” the strip along the beacons and corners of the excess mixture. After partial setting, small unevenness and voids are removed with a float. After the completion of finishing work, artificial drying of the atmosphere in the room is unacceptable, a high level of humidity must be maintained for at least 5-7 days.
When performing cement preparatory plastering for laying tiles, there are some peculiarities. Such a coating is heavier, therefore, it is necessary to include in the work the mechanical forces that hold the plaster layer on the wall. This can be done by invoicing the surface, applying numerous notches and chips, or using a galvanized plaster mesh. To fasten it, be sure to use special fasteners:
- Anodized self-tapping screws, unlike conventional screws, will not lead to the formation of rusty spots;
- Special plastic screw caps provide a secure hold even in thin partitions.
Plastering work from the street side is carried out in two stages. First, a layer of base plaster is applied, a fiberglass mesh is glued to it, which is covered with a base layer of 3-5 mm. After that, a mixture is applied that does not have such a pronounced adhesion, but has water-repellent properties. To improve the aesthetic perception, the finishing plaster can be coated with a special paint after drying..