- What is the specificity of aerated concrete
- What type and format of blocks to choose
- Base for aerated concrete house
- Block processing
- Masonry technology
- Formation of openings and overlap arrangement
High-quality aerated concrete is one of the best building materials that combines sufficient load-bearing capacity with low thermal conductivity. This material is quite specific and requires adherence to masonry technology for a high-quality result..
What is the specificity of aerated concrete
Aerated concrete or gas silicate is a material of finely seamed masonry, the task of which is to form the most monolithic structure of the walls. It can be compared to gluing together joinery, but only on the scale of the whole house..
In essence, aerated concrete is a natural mineral such as pumice, recreated in artificial conditions. The chemistry of this process is quite complex, but the production technology is well mastered, which allows us to supply materials of very high quality to construction sites, you just need to learn how to choose the right one. It is important not to confuse gas silicate with foam concrete: with all the external similarity, these are materials with completely different qualities.
Aerated concrete is very good as a load-bearing material for walls: it does not give significant shrinkage, has high compressive strength, but only if the load is sufficiently evenly distributed over the block. Its thermal conductivity is lower than that of wood, the material is not characterized by internal microconvection, and a closed pore system excludes capillary suction of moisture to a great depth.
Gas silicate blocks are deservedly popular among those who know how to work with them. When handled correctly, this material provides high precision and construction speed at a relatively low cost. One of the main features of aerated concrete buildings is a low load on the foundation, which allows building in a complex geomorphological environment. But this requires knowledge of technology and a special tool for cutting blocks and applying glue..
What type and format of blocks to choose
Aerated concrete blocks are classified by type and size according to GOST 21520–89. The form of designation of aerated concrete established by him consists of the type of block, strength class, grade of average density and frost resistance, as well as the category of application. If the seller does not explicitly indicate the nomenclature designation, then, most likely, we are talking about products of dubious quality, for example, manufactured in local artisanal conditions.
For convenience, aerated concrete blocks are designated with an index D with a three-digit number indicating the average density and the conditional limit of breaking capacity. This does not in any way replace the need to indicate the exact designation according to the standard, however, it allows you to distinguish separate classes of blocks: for the construction of load-bearing walls, filling the cells of the frame structure, or for insulation. The higher the number in the reference designation, the higher the bearing capacity and the lower the energy efficiency of the blocks.
The sizes of the blocks can be selected according to standard norms, taking into account the required load-bearing capacity and heat transfer resistance. Manufacturers are also willing to cut blocks according to individual orders with certain delivery volumes. In general, the overall dimensions of aerated concrete are determined by the layout scheme, which must be thought out in advance for odd and even rows. In the process of calculating the layout, special attention should be paid to the nodes of the ligation of the masonry in the outer and inner corners, perhaps blocks of non-standard sizes will be required here. By the way, they can be made locally by cutting or gluing a whole block with an additional element.
Base for aerated concrete house
The foundation for an aerated concrete house must have dimensions that exceed the dimensions of the box by the thickness of the thermal protection belt and taking into account certain tolerances for geometry distortion. With proper installation, this tolerance is about 20 mm per 10 meters of the length of each enclosing structure and no more than 40 mm difference in the length of the diagonals.
Most types of foundations are suitable for building from gas silicate. In reality, reinforced concrete foundations for aerated concrete are greatly underestimated in cross-section compared to brick or wooden houses, guided by considerations of ensuring a sufficient thickness of protective layers and correct distribution of reinforcement for effective perception of loads. This approach is acceptable only in a civil self-construction building with a height of up to 2 floors, more serious objects require a detailed calculation of loads, taking into account geomorphological data.
The standard version of the foundation for an aerated concrete house is a MZLF 80–100 mm wider than the predicted wall thickness, which for the middle climatic zone fluctuates in the range of 400–550 mm. Of this tolerance, at least 70 mm is allocated for the device of an internal protrusion for lag or dressing with a tie, the remaining 10–30 mm serve as a correction for geometry curvature. At the same time, aerated concrete can be released beyond the foundation line up to 1/4 of the block width, although this is not recommended simply for reasons of common sense. It is better to provide an excess protrusion of the base for a more technologically advanced installation of insulation of the foundation or basement.
Aerated concrete is easy to process: in general, each block is the result of cutting a huge array. On-site processing will have less surface cleanliness, but even hand tools are often enough to comply with technological rules.
Usually, aerated concrete is cut using a hand saw with a special blade. In this case, the correctness of the cut is controlled by an eye, which cannot be called a method of confident control. In more or less organized construction teams, blocks are sawn using a device that acts as a miter box. Correct processing of aerated concrete reduces glue consumption and well contributes to adherence to the basic principles of technology.
There are some differences in working with blocks with flat edges and special products with a profile poke, designed for groove-and-tenon connection of vertical joints. In this case, no glue is applied to the vertical surface of the blocks, but it may be necessary to make a longer block by gluing the two pieces together. Usually, groove-ridge blocks are used in the outer heat-insulating lining, where a slight blow-through will even be useful.
Processing blocks is not limited to cutting them. According to the original technology, the masonry of gas silicate blocks must be reinforced, for which it is necessary to manufacture technological grooves. Cutting them during the production of blocks means significantly increasing the cost of the material, therefore, grooves for reinforcement are usually made locally. This can be done either with a hand scraper or with a wall chaser..
On a note:despite the apparent homogeneity, the structure of the blocks varies from surface to core. This is due to the manufacturing technology, namely the cutting process, due to which the structure of the surface layer is disturbed. Because of this, blocks can, for example, more intensively absorb moisture to a depth of 20–30 mm, which, in general, does not critically affect the strength characteristics. Nevertheless, for this technology, a large format of blocks is more preferable, limited only by their weight, because one person must freely handle the elements of the masonry in the process of performing work..
In terms of the masonry technique, aerated concrete is very similar to silicate brick. Of course, there are fundamental differences in the performance of tie seams, but in general, the alignment technique is similar to the classic two-row masonry: you can use only mooring cords and “Egyptian” triangles.
There is a lot of controversy about how to properly tie the blocks between the rows. The best guideline in this matter will be the standards of the original technology, according to which, for a reliable bond, a shift of vertical joints of at least 70% of the block height is required, and when laying walls up to 200 mm thick – at least 1/3 of their length.
The brickwork of the walls of industrial and technical premises is monolithic; a two-layer scheme is provided for residential buildings. This method of masonry is beneficial not only in terms of improving energy efficiency, it also helps to shape the geometry of the internal and external walls independently, due to which the accuracy is comparable to that of modern concrete panel houses. The inner layer of gas silicate performs the main load-bearing function, its thickness is determined by the predicted loads. The outer layer is laid out from lighter blocks, the sufficient width of which is established by thermal engineering calculation.
The very same block laying technique is quite simple. The first row is laid on a thicker layer of glue in order to level the unevenness of the base. When the starting plane is removed, and this may be the second or even the third row, the laying continues to be performed using fine-seam technology. A thin seam of liquid glue is applied to the surface of the laid blocks using a special device. The block to be installed is dipped into the container by the sides with which it will contact other elements, and is positioned in place with a tolerance of about 5 mm. After that, the block must be moved until a characteristic squeak appears between the contacting surfaces, and then finally align in the plane of the wall and in level using a mallet. The protruding excess glue must be rubbed back with force with a spatula, this limits the absorption of moisture through the edges of the blocks.
Formation of openings and overlap arrangement
One of the typical flaws of an aerated concrete house is the reinforcing lintels of the openings. Their calculation is carried out according to the standard methodology: the lintel is provided with absolute rigidity, while the weight of the structure above the opening should not exceed the permissible load on the blocks for a certain support area and the self-supporting capacity of the masonry. Because of this, lintels in aerated concrete houses are longer than usual, respectively, the number of gaps in thermal protection increases relatively. In practice, the issue is solved by a thermal break device in the lintels: either by using special aerated concrete trays as a fixed formwork, or by inserting expanded polystyrene partitions before pouring. The side edges of the opening can be laid out with the formation of a quarter, for which either blocks of a special shape are used, or a flange of the required thickness is glued.
Gas silicate blocks fully manifest their bearing properties only in the presence of a structural element that distributes the load. As a rule, for this purpose, a reinforced concrete belt with reinforced reinforcement is used – 250-300 mm high and the thickness of the entire load-bearing layer of the wall. Armopoyas is a serious vulnerability of aerated concrete buildings in terms of thermal protection. To eliminate the cold bridge, you can use the same techniques as when installing jumpers in openings: foam dividers or special trays, in the case of erecting two-layer masonry, the outer wall simply closes the ends of the belt and floors.