- What you need to know
- What are the options for plaster
- Spray plaster
- Manual gypsum plaster
- Cement and cement-lime plaster
Aerated concrete walls are initially quite flat, no significant efforts are required to level them. Plaster is one of the best preparatory finishing methods in such cases, from our review you will learn about the methods of plastering and the materials used..
What you need to know
Aerated concrete is a very specific material that requires strict adherence not only to masonry technology, but also to a number of rules for the construction of protective coatings. Due to this specificity, aerated concrete has overgrown with many myths, most of which are only partially true..
The most common misconception is the inadmissibility of using cement-sand mortar for plastering. Say, due to too strong water absorption and smoothness of the walls, the plaster will not be able to normally adhere to them during the application process and will necessarily peel off over time due to a lack of moisture for normal cement hydration. In fact, the hygroscopicity of aerated concrete is greatly exaggerated: it really actively absorbs moisture, but this process is greatly slowed down after saturation of the surface layer to a depth of 10-15 mm.
Another myth stems from the fact that aerated concrete walls practically do not require leveling, and therefore the thickness of the plaster should not exceed the minimum values of 6–8 mm. In practice, the tolerances for aerated concrete construction are much higher, and the thickness of the adjustment layer of plaster can sometimes reach 20–25 mm, which is absolutely normal. In addition, an increase in the thickness of the plaster layer may be necessary to eliminate blow-through and normalize gas exchange, as well as to relieve the wall covering from shock rumble.
When decorating houses made of aerated concrete, it is imperative to make a pause between indoor and outdoor plastering work – this is no longer a myth. The best option is to tie the box with an armored belt and cover it with a roof, and finish it the next year. After the air temperature has stabilized at a level above +10 ° C for at least two weeks, an internal preparatory finish is carried out, and with an interval of 20-30 days – an external one. During this time, the excess moisture, which the walls have managed to absorb, manages to evenly distribute over the thickness of the wall and erode.
What are the options for plaster
One of the most budgetary methods for rough finishing of gas silicate is the classic plaster with cement-sand mortar of the M15-M25 strength grade. The main disadvantage of this method is the need for careful preparation of the walls and strict adherence to technology. However, in the end, significant cost savings can be achieved, but at the same time, finishing work can only be continued after a full set of plaster strength for 28 days. For internal work, it is allowed to use cement-lime mortars, in which two-thirds of the cement used is replaced with fluff.
Manual gypsum plaster on lighthouses is the most common method for rough leveling of aerated concrete buildings. The method is used mainly for interior work, although compositions for facade decoration are also quite common. A distinctive feature of gypsum plaster is that it uses factory-made mixtures, which are equipped with detailed application regulations, which means there is some guarantee of the quality and durability of the coating. With this method of finishing, a smooth and even surface is formed, suitable for applying Venetian plaster or painting without additional puttying..
A mixture of cement-polymer binders is a kind of analogue of gypsum plaster. Due to its increased resistance to weathering, this finish is ideal for the facade, but can also be used in rooms with high humidity: baths, swimming pools, kitchens and bathrooms. Mixtures of this kind are the most expensive, therefore it is advisable to purchase them for covering walls made using the technology of seamless or fine-seam masonry, characterized by smaller errors of flatness and geometry.
Recently, gunning plastering of walls is gaining popularity, especially in large cities, where professional finishing teams work. As a spraying material, gypsum or cement-polymer plaster is used. This method of rough finishing is distinguished by a high speed: the productivity of a team of plasterers with one shotcrete machine can reach 300 m2 per work shift, while finishing works can be carried out after 5-7 days.
Although machine spraying of plaster can be done independently only if it is possible to rent highly specialized equipment and if you have certain skills, it is recommended to take a closer look at this method first. First of all, for the reason that when gunning does not require a thorough preparation of the walls: there is no need to install beacons, and the problem of relatively weak adhesion is solved due to the intensive compaction of the mixture when it hits the wall. The only preparation requirement is the treatment of aerated concrete with a primer for highly absorbent surfaces..
When spraying plaster, the uniformity of the application is controlled automatically, it is only necessary to maintain a constant working speed. As a rule, spraying is carried out in several stages by sequential application of layers 5–7 mm thick. At the same time, the total thickness of the coating is practically unlimited, therefore, by gunning, it is even possible to apply heat-saving plaster with a perlite filler. Shotcrete is also well suited for throwing in a warm “fur coat” for facade finishing.
Manual gypsum plaster
Before plastering with factory gypsum mixtures, the capital preparation of aerated concrete is carried out. Since the hydrophilicity of gas silicate at the first stages of wetting is extremely high, a significant part of the water necessary for normal hydration is taken from the plaster mixture. This effect is not as pronounced as in cement compositions, however, with insufficient preparation after drying, a web of cracks may form, if the walls were not prepared at all, delamination is guaranteed..
Preparation before applying gypsum plaster consists in a generous treatment of aerated concrete with a primer for highly absorbent surfaces. This should be done with a brush, carefully saturating the wall until most of the applied primer begins to flow down it. For facade work, it is possible to recommend the use of high-pressure car washes, while instead of a primer it is better to take a concentrate or contact emulsion diluted with water according to the instructions. After use, the device itself must be desalinated by pumping a large amount of clean water through it.
The second prerequisite when working with gypsum plaster is to strengthen the finishing layer with a reinforcing mesh. If the plaster is carried out without beacons, the mesh is laid about 2/3 of the total layer thickness closer to the base. Thus, plastering work is carried out in two stages: wiping and gluing the mesh, and then applying a cover layer. If the plaster is carried out on the beacons, the mesh must be glued to the aerated concrete, which is previously wiped off with a gypsum mixture with a minimum layer thickness. After the installation of the lighthouses, the main layer is applied, then the lighthouses are removed, the furrows are sealed, and at the final stage the walls are putty using fiberglass with a density of 40-50 g / m2.
Cement and cement-lime plaster
Cement-based formulations are the most demanding for surface preparation. It is necessary not only to limit the absorbency, but also to provide increased adhesion of the cement to the relatively smooth surface of the gas silicate. For these purposes, after the walls have been impregnated with a primer that limits absorbency, they are coated with an adhesive compound such as “Betonkontakt” containing stone dust. You can also use a facade primer of the same type, but not indoors, because often volatile toxic substances are present in the composition..
The process of performing cement plaster itself differs from the basic technology only in that the primary spray layer is made thinner using a solution of a very liquid consistency, while a regular broom is often used instead of a bucket. It is possible to spray in the classical way, but in this case, a set of plasticizers should be added to the solution to normalize the setting. When covering aerated concrete walls with cement plaster, the use of a reinforcing mesh is mandatory, as a rule, it is fixed at the stage between spraying and the installation of beacons.
Of all the proposed methods, the process of applying cement and cement-sand plaster is the most time consuming, but at the same time it is it that allows you to preserve the limited vapor permeability of the walls, which is very often chased by developers. However, gypsum plaster, which is capable of reversibly sorbing excess moisture, copes with the normalization of the microclimate..