Distinctive feature houses built from aerated concrete blocks are lightweight, allowing a little savings on the foundation, and good thermal insulation characteristics, thanks to which sufficient thickness walls can be done without additional insulation. But, like all other wall materials, aerated block masonry has its own nuances.
If you decide to build a house from aerated concrete, we recommend that you familiarize yourself with the nuances and subtleties of the foundation, construction of walls, ceilings, cladding and finishing of a house made of aerated concrete.
The light weight of a house made of aerated blocks can help save on the width of the foundations, but that’s all! The deepening of the foundation and its reinforcement must be carried out in accordance with all the rules.
The most common problem associated with foundations is the appearance of cracks in the walls after the first winter. You can often come across the misconception that cracks appear due to the low weight of the blocks, as a result of which the house seems to “float”. Even more erroneous is the recommendation to be sure to fill under such houses. foundation slab. In conditions of frost heaving, the heaving forces will be greater the larger area contact of the soil with the underground part of the building. With a significant increase in level groundwater the Archimedean force will be proportional to the volume of the part of the building immersed in the ground. In both cases slab foundation won't help anything.
The main nuance of constructing a foundation for the construction of a house made of aerated concrete is its insulation. A properly reinforced, sufficiently deep foundation is not a guarantee that there will be no cracks in the walls after the first winter. Especially if you have a basement.
Let's look at a real case using a specific example.
Cracks in the corner of the building not high from the floor.
Cracks in the corner of the building at the ceiling level of the first floor.
There is a crack in the corner of the building - the middle of the floor.
The walls are built from high-quality aerated block. The foundation is strip, reinforced. There is a basement. Before the onset of cold weather, the house was covered with a roof, windows and doors were installed.
The causes of cracks were:
As can be seen from the above list of factors, it is highly undesirable to leave a newly built house for the winter without insulation or heating. The limiting depth of soil freezing is determined by the presence of molten magma in the center Globe. The top (freezing) layer of soil is a kind of jacket, deeper than which the cold cannot penetrate due to the presence of heat in the center of the planet. Excavation of soil under the basement opens the way for freezing to even greater depths.
The method for solving this problem is obvious - if the building is not put into operation before the onset of cold weather, the foundation (especially its basement part) must be carefully insulated. This is critical for heaving soils. Insulation can be done by backfilling expanded clay gravel or blast furnace slag, spread mineral wool mats or straw, etc. It is highly undesirable to backfill the pit openings (trenches) with ordinary soil. Preference should be given not only to materials that are not heaving, but also to warmer ones.
Perlite sand is ideal. If it is not possible to purchase it, you can limit yourself to the usual one. In this case, the negative heaving effect on the underground part of the basement walls will be completely eliminated.
The appearance of cracks not in winter, at the height of frost, but in spring, is associated with the fairly high stability of the soil in a frozen state. During thawing, the soil is reconsolidated, forming shrinkage. The result of these processes is shown in the photographs above.
For the construction of load-bearing walls from aerated concrete blocks, blocks of grade D500 and higher are used. The numerical index means volume weight in kg/m3. For internal non-load-bearing walls and partitions, the use of grade D400 is acceptable. The lower grade D300 is usually used as insulation for walls made of more durable material.
When the number of floors is three or more, blocks with a grade of at least D600 are used.
The thickness of the walls is determined thermotechnical calculation. Thermal resistance wall is determined by the sum of the coefficients of resistance to heat transfer internal and outer surfaces walls, as well as each layer of the wall itself.
Let's consider thermotechnical calculation resistance to heat transfer of a wall made of D500 blocks 375mm thick, insulated with a 50mm mineral wool board.
The thermal resistance of a wall layer to heat transfer is determined by dividing the layer thickness by the thermal conductivity coefficient (see table).
Very often in advertising brochures you can find a thermal conductivity coefficient for the D500 brand equal to 0.1. Is not more than marketing ploy. This value is either deliberately rounded down or simply provided for a completely dry block condition. In real operating conditions, the thermal insulation properties are worse - their values are given in the column calculated coefficients. The letters “A” and “B” indicate the humidity zone corresponding to the construction site. For the coasts of large bodies of water, zone “B” is accepted, for other places, as a rule, zone “A”. The higher the water saturation of the material, the worse its thermal insulation properties.
Characteristics of other materials are given below.
The sum of the coefficients of resistance to heat transfer by wall surfaces (external and internal) is equal to 0.158 W/mS.
We determine the thermal resistance for masonry made of D500 blocks with a thickness of 375 mm (0.375 m) in the humidity zone “B”:
0.375 / 0.16 = 2.344 W/mS
Insulation with a 50mm (0.05m) mineral wool board will give the following indicators:
0.05 / 0.09 = 0.556 W/mS
The total heat transfer resistance of the wall will be:
R=0.158 + 2.344 + 0.556 = 3.058 m2/W*S
Is this result enough? It depends on the climatic zone of construction. Determination of the required value of R is carried out according to table. 4 SNiP 02/23/2003. The calculation is relatively cumbersome, it’s easier using any search engine Find out the required R value for your region. The higher the value of this indicator, the warmer the house.
Reinforcement of walls made of aerated concrete blocks is a mandatory measure aimed at reducing the likelihood of cracks appearing in the walls. Leading manufacturers of aerated concrete blocks (for example Aeroc) have developed over many years of experience general recommendations for wall reinforcement.
In general, the first row, the window sill and above the window rows, the row at the level of the mauerlat and the middle of the gables are subject to reinforcement. It is also recommended to reinforce the 1m support area of the lintels.
Saving on wall reinforcement can end in disaster.
Reinforcement is performed with two reinforcement bars with a diameter of 8-10 mm of class A-III (A400) or galvanized Aeroc perforated strip with a cross-section of at least 1x15 mm. In the first case, you will need a groove device for laying reinforcement.
Fines are made with hand scrapers or power tools (grinder, grinder, jigsaw, reciprocating saw or even a milling cutter).
When reinforcing with perforated strip, a fine device is not required.
Filling of grooves with reinforcing bars and masonry joints with perforated strip is carried out with the same glue that is used for the construction of walls.
For houses with walls made of aerated concrete blocks, the use of all types of floors is allowed: wooden, lightweight (for example, Teriva), prefabricated (from hollow-core slabs), monolithic.
In case of device monolithic ceiling It is allowed not to make a monolithic belt. The latter is required for supporting prefabricated floor slabs.
In the case of lightweight overlap, it is advisable to make a monolithic belt in a simplified format. As formwork, two rows of 100mm thick blocks are installed with glue in such a way that a cavity is formed between them along the walls. A reinforcement frame is installed into it, consisting of four longitudinal reinforcement rods (usually 10-12mm class A-III or A400) and transverse clamps and filled with concrete of class B15-B25. Before pouring concrete, be sure to let the glue dry, otherwise there is a risk of spontaneous demolition.
In cold regions, it is advisable to pay more attention to insulating the outer edge of the belt. In this case with outside a series of blocks are laid. On the inside, formwork is installed.
When constructing a wooden floor, beams may be supported directly on the masonry or on a wooden lining.
The wooden floor, which is usually installed under the attic (and not under a full floor), does not place large loads on the masonry, so you can do without an armored belt, but the supporting row of gas blocks must be reinforced.
Separately, we note that laying one or more rows brickwork Although it helps distribute the load from beams or floor slabs, it is not a full replacement for the reinforced belt.
When building a house on subsiding soils, even with wooden floors refusal of the armored belt is highly undesirable.
An important nuance of houses built from aerated concrete blocks is the critical need for free vapor permeability of the walls. Otherwise aerated concrete block picks up moisture from the air (since it has high absorbent properties) and sharply loses its thermal insulation efficiency. This entails the requirements for cladding, external insulation, and interior finishing.
Manufacturers of aerated concrete blocks strongly recommend for exterior finishing walls ventilated facade systems or cladding facade brick(silicate is suitable) with a ventilated gap of 20-40mm. Ventilation of the gap is carried out by installing holes in the lower and upper parts of the wall. The area of the holes should be 1% of the wall area.
Connection facing masonry with a wall made of aerated concrete blocks is done using spiral nails, ordinary galvanized nails, at least 4 pieces per square meter hammered in pairs at an angle of 45 to each other, perforated strip releases from masonry joints.
Ventilated fastening facade systems is carried out in accordance with the requirements of the manufacturer of this system.
For external insulation of walls made of aerated concrete blocks, it is necessary to use vapor permeable insulation. Rigid or semi-rigid mineral wool slabs work well. All types of polystyrene foam should be abandoned, since its vapor permeability is at least 10 times worse than mineral wool.
The same requirements are imposed on interior decoration - vapor permeability. It is better to use light plasters as plasters. gypsum mixtures. Particular care should be taken when handling acrylic finishing putties, instead you should pay attention to gypsum ones. For painting surfaces, it is preferable to use water-based paints rather than acrylic or latex paints.
Resistance of structures to cracking is the key safe operation buildings. Prevent the formation of cracks in aerated concrete walls and choose a method for eliminating it, perhaps having an idea of the parameters of cracks and the nature of their formation.
A crack is a structural defect resulting from the occurrence of critical stresses in the composite. Stress can be caused by external aggressive factors or internal imbalance of the system. Simply put, if the composition of aerated concrete is incorrectly calculated, the properties of the finished blocks can be deteriorated. If the strength of a block or monolith does not meet the specified strength, the wall begins to collapse. Cracks can be divided into two types:
The main parameters of a crack are its depth, opening width, and length. The location of the crack is important. There are regulatory documents that specify acceptable and unacceptable cracks for different types structures, including vertical load-bearing and enclosing elements. In addition, regulatory documents establish requirements regarding crack resistance for concrete itself and products made from it.
The nature of crack formation has been the subject of the works of many researchers. Aerated concrete is a complex composite with a porous structure, which, on the one hand, compensates for shrinkage deformations, but on the other hand weakens mechanical properties systems. The main reasons for the formation of cracks can be divided into three groups:
To prevent the occurrence of cracks, we will analyze each group in detail.
Compliance with everyone's requirements regulatory documents, as well as attracting highly qualified specialists is prerequisites for any aerated concrete production. Ordinary consumers should choose products from trusted suppliers who have proven themselves in the market building materials. When choosing blocks, you need to familiarize yourself with their characteristics. Size, density, strength, frost resistance - all these indicators are indicated in the quality certificate for the block. The passport or certificate of conformity must bear the blue seal of the manufacturer, and in some cases the mark of the organization that conducted the tests. Quality indicators must meet the requirements of your project.
Advice: If your project involves the construction of a building higher than one floor, you should choose aerated concrete with a density D of at least grade 500.
It is worth noting that a high-quality autoclave unit has light color, homogeneous structure and smooth edges. If there are stains on the block, dark spots, oily film, then it is better to refuse the purchase.
If the technological operation of swelling the aerated concrete mass is followed, the pores of the block will be smooth, round, closed, evenly distributed throughout the body of the element. When purchasing, pay attention to the cut of the block. The presence of pores that clearly differ in size do not have round shape, indicates poor thermal conductivity, as well as low sound insulation properties.
When using monolithic aerated concrete, you need to pay attention to the surface of the mixture. The separation of water indicates non-compliance with the recipe. Monolithic aerated concrete is more susceptible to shrinkage deformations. In order to avoid cracking of aerated concrete walls during monolithic concreting, it is imperative to comply with all preparatory work(clean formwork, absence of cracks and holes), as well as care of hardening concrete.
The foundation has a major influence on the operation of all building structures. From correct device The durability and reliability of the structure depends on the foundation. If aerated concrete walls are cracked, first of all you should pay attention to the condition of the foundation. A “weak” foundation undergoes irreversible mechanical changes; in other words, it “floats.” In this case, deep vertical cracks appear on the walls. The location of the cracks can be different, most often in the middle of the walls. Such cracks are critical. They weaken bearing capacity walls and pose a threat to the overall strength of the building.
Attention! If cracks occur due to a “weak” foundation, it is prohibited to repair them. In 50% of cases, it is necessary to strengthen the foundation and soil with the subsequent elimination of wall defects. In 10%, the structure is dismantled.
When plastering aerated concrete walls, it is not advisable to use conventional plasters. They are prone to cracking on porous substrates. Preference should be given to plaster compositions special purpose. Such compositions do not transfer moisture to the porous block, and, as a result, are not a catalyst for the formation of shrinkage deformations leading to the appearance of cracks.
The service life of the building depends on the correct operation of the structures. If you want to make major changes, you should take into account the characteristics of the blocks and realistically assess the possibilities of carrying out a certain number of works. For example, if you decide to build a ventilated facade, and a block with a density of D 500 is used for the walls, then it is better to abandon the idea. The façade structure is experiencing strong dynamic loads, therefore, weak wall strength will lead to the formation of cracks in aerated concrete walls.
When using newly installed walls, minor defects may form, such as small cracks in aerated concrete masonry. These cracks are not dangerous and can be easily repaired. They occur when exposed to atmospheric humidity, as well as aggressive reagents. environment. You can avoid the occurrence of small cracks in aerated concrete masonry by using the device protective coating(plaster, putty, paint).
If it is still not possible to prevent the formation of cracks, there are a number of methods for eliminating them independently. So, what to do about cracks in aerated concrete? First, you need to understand what kind of crack you are facing: mechanical or shrinkage. Mechanical indicates a problem in the base or foundation, or a “subsidence” of the entire structure. In this case, it is necessary to conduct an inspection of the foundation, as well as the basement part. You will have to expose part of the foundation under the crack. If possible, determine the depth and length of the crack, and also understand the rate of its growth. Shrinkage crack is less dangerous. It has a small opening width and is often called hairline. For example, if cracks appear on aerated concrete walls in winter, then most likely you are dealing with ordinary shrinkage defects that form due to temperature changes in the operating environment. Such cracks can be easily repaired.
Procedure for eliminating small cracks in aerated concrete masonry:
If the crack is deep, after jointing it is worth reinforcing the seam with nails, mesh or wire. Then seal the crack with a solution using coarse aggregate, and in some cases chemical additives. Stabilize the seam (install a plywood sheet on screws opposite the seam).
If the crack is very deep, then you should seek the help of specialists, since do-it-yourself repair can only make the situation worse.
Remember! Your strong home is your reliable fortress!
One of the most effective and cheapest wall materials, which are used in private construction, are considered aerated blocks. The advantages of such products are obvious - they are sufficient strength, good heat and sound insulation, resistance to high temperatures, fungus and mold, and the price of such materials is quite affordable.
Some builders who used aerated concrete to build walls may have noticed various defects appearing on the walls, especially after wintering. Many people are looking for an answer to the question: why do cracks appear in aerated concrete? Some attribute this phenomenon to wall shrinkage, but in fact this is not the only reason. Let's look at the answer in more detail.
We have figured out the reasons for the appearance of cracks, and now we will get acquainted with the technology of masking them and ensuring the solidity of the wall.
The affected area must be cleaned of dirt, dust removed with a vacuum cleaner or spilled with water. Next, the crack is primed, and when the liquid is completely dry, it is sealed. cement mortar. If the damage is significant, remove dirt, clean and prime the crack, and then fill it with a solution containing aerated concrete particles.
ElenaRudenkaya (Builderclub expert)Good day, Sergey.
You see, there is no point for us to tell you something that doesn’t really exist or to somehow hide something that we can help eliminate. On the contrary, we want you to find the causes of your cracks, eliminate them and live in your beautiful house many more years to come.
I will try to explain to you and answer all your questions.
1. Yes, your monolithic slab is a whole mechanism (structure), which has its own loads, deformations, and it has its own “work”. It works both in deflection and compression. This is a structure that does not have a rigidly fixed frame and adapts to work depending on various influences. According to the project, you should have calculated and taken into account all these deflections. In your case, it also works on vertical forces (“plays” like a raft rises and falls up and down on small waves). The hot water level rises in the spring, the slab, together with the grillage and piles, rises up in the garage area, since the piles do not support the walls at the entrance to the garage. There is no basic drainage system from the rains that wash away this same part. The water receded into the reservoir after spring, and the slab settled into place like a raft. But, for example, if we talk about walls, then they have a rigid frame and it is enough for the slab to rise only 2 - 3 mm from the design level, then the wall begins to break and a crack occurs. Where different direction cracks. You yourself described everything correctly about the directions of the cracks. The slab rose, a crack opened towards the roof, the slab fell into place, the crack moved in balance along the second wall, only to open towards the ground. It’s strange that the builders can’t explain this to you.
2. We can absolutely say that if during construction you did not pour the piles onto a solid foundation, and they “hang” or float in the water, then 2 m is very little. They are simply connected by a grillage, loaded with a slab of variable cross-section and in one part the weight of the house, in the other - the garage, and accordingly there are vertical movements from the hot water. They build houses in swamps, but at the same time they deepen the piles at least 5 - 6 m. A specialist cannot help but know this.
3. It is very bad that the floor slab has a variable cross-section of 25 mm and 45 mm, although the house and garage have different loads, so a monolithic slab cannot work as a single whole. And the tension was initially in the foundation, and then went along the walls (what your specialist is talking about), but since the monolithic slab has a certain margin for deformation, therefore, no cracks have formed in it yet. But you see, this is temporary. With such progress, everything can happen very quickly.
The sooner you start, the better it is to follow our recommendations described above. This is the first and main thing we can advise you. It is necessary to monitor the house after installing the blind area for several years, so that there are no more openings and formation of new cracks. If this does not help, then we have another very difficult way for builders to strengthen your piles in the garage area. It may be easier to dismantle the garage than to do what I’m writing about, but more on that later. And we are almost sure that the blind area and drainage of hot water will be sufficient in your situation.
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