- Porous blocks: characteristics and essence of the material
- Varieties and formats of blocks
- Use with care: how to avoid building defects
- Correct wall laying technique
- Recommended floor types
There are not many ways to integrate the load-bearing structure with thermal insulation, so porous ceramic blocks are definitely worth considering. Today we’ll talk about the properties of this building material, the peculiarities of working with it, the technique of masonry and wall decoration of buildings of different storeys.
The situation with porous ceramic blocks is quite ambiguous. Distributors praise warm ceramics, while some well-wishers scold her. Let’s try to get to the bottom of the truth, it’s not for nothing that these blocks are so widespread.
Porous blocks: characteristics and essence of the material
The main problem in the production of red building bricks has always been a high degree of rejection: in the process of firing, the clay mass tends to change its linear dimensions and deform, moreover, a considerable amount of breakage is formed during transportation. To create building blocks of large sizes from such material was, for some time, a very difficult task..
The question was solved by the method of extrusion molding of ground clay mixture. The composition of the latter can vary depending on the mineral additives and pore-forming inclusions. Thus, in addition to the presence of large vertical channels that lengthen the path of heat outflow, the whole brick itself can have micropores that increase the resistance to heat transfer..
At its core, warm ceramics are nothing more than a kind of hollow brick. But the linear dimensions of the blocks are nine or more times larger, which gives a tangible increase in the speed of wall erection. The voidness is also much higher and can reach 80%, this is a huge plus in terms of thermal conductivity and in terms of reducing the structural load on the foundation..
Oversized blocks, oddly enough, do not have high dimensional tolerances. First of all, because the cellular format, in combination with mineral and pore-forming additives, negates shrinkage during firing, besides, some types of warm ceramics can have polished ends. In general, the deviation from the stated dimensions is up to 2–3 mm for each block. Material is packed on pallets rather than in bulk, so the amount of breakage during transportation is minimized.
Varieties and formats of blocks
There are two main types of PCB – for insulation and masonry of the bearing layer. The addition of ground wood flour to the clay at the stage of mixture preparation results in its burning out during firing. The brick becomes brittle and is not suitable for the construction of the supporting layer (strength grade M30-M50).
Various kinds of mineral additives, which have good sintering properties along with clay, can increase the strength to the M100 grade, which makes the warm ceramics suitable for laying the pillar of external and internal load-bearing walls. The thermal conductivity of such blocks is higher, but this is eliminated by a relatively thin outer layer of insulating lining..
In construction practice, materials are usually combined in one wall. The inner load-bearing layer occupies 50–70% of the total wall thickness; it is laid out in blocks of increased strength. It is followed by a layer of 20-30% of the total thickness with a high resistance to heat transfer, and the structure is completed by an external cladding in half a small-sized brick with a voidage of about 30%. Such a scheme is generally accepted, and later we will describe its advantages..
Ceramic blocks are available in a wide variety of formats. Regardless of the material, structure, blocks are divided into basic masonry and additional facing. Both types have a strict direction of masonry: grooved side edges complicate the outflow of heat by convection, and such a connection of blocks of the same row is necessary. Choosing a format in advance, you can be guided by the final thickness of the bearing walls 25, 38, 44 and 51 cm.Facing blocks provide a thickness of the heat-shielding layer of 8, 12 and 20 cm..
Use with care: how to avoid building defects
The main argument of critics of porous ceramic blocks is insufficient compressive strength. “Experts” tend to compare the incomparable and give out the low strength of the insulation blocks for the complete technological unsuitability of the material as a whole. However, the combination of different brands allows you to correctly distribute the load along the wall: its main part is taken over by the inner bearing layer, and the outer cladding, although it does not perceive the axial vector directly, serves for the general strengthening of the array.
Technically, such a three-layer wall is equivalent to a pillar of two and a half solid bricks of grade 100, while in terms of thermal conductivity it corresponds to 60–80 cm of hollow bricks. Therefore, the construction of a PCB in four floors (including the attic and basement), with proper design, is quite real. If the building is being built on a reinforced concrete frame, there are no restrictions on the number of storeys.
Another argument against warm ceramics is their insufficient holding capacity. The blocks are really fragile and practically do not hold standard dowel-nails, which makes it difficult to finish using hinged systems. Special fasteners for aerated concrete and chemical anchors come to the rescue: in the end, they do not cost much more, at the same time, the benefit from a light and warm wall is much more important.
One of the specific subtleties of working with the PKB is cutting grooves for laying electrics or pipes. A common mistake is chipping with a hammer drill in impact mode, leading to strong crumbling of a porous wall. You should work only with chasing cutters or angle grinders, but it is better to hollow out the channels by hand – with a chisel and a hammer, this is not much longer, but it will save you from dust.
It is impossible to argue with the fact that PKBs require the involvement of qualified personnel for the construction of walls. Warm ceramics are only part of the technology, but not its basis. The material must be of high quality and certified, this is not even discussed. But the masonry technique, the final protective cladding, the use of special materials – all this is of no less importance so that the walls made of warm ceramics are really warm and correspond to the declared characteristics..
Correct wall laying technique
One of the alleged disadvantages of porous blocks is the partial elimination of porosity during the masonry process due to the cement slurry spilling into the cells. This phenomenon is eliminated by using a special mesh, which is placed in each aisle and retains the binder. Ordinary fiberglass mesh can be used for facade plastering, but experts recommend using basalt mesh in order to increase the uniformity of the masonry array.
Strictly speaking, cement mortar or sand concrete is not used in the masonry of warm ceramics. They have insufficiently high resistance to heat transfer, therefore, in technological construction, liquid adhesive mixtures are used for sanded blocks and lime mortar for unpolished ones. The dry block is dipped in a solution or glue mixture, the adhered layer is quite enough for reliable fastening of the rows.
Cold bridges are not completely excluded, but their number is minimized. To completely eliminate thermal conductivity between layers of masonry, it is customary to lay 30–50 mm of extruded polystyrene or cheaper PBS. At the same time, the vapor permeability of the wall is artificially limited by membranes of different types, and on the outside of the separator there is a gap of 30–50 mm for air. If there is no insulation between the layers, when laying each row, roll out a 10 cm strip of foamed polyethylene.
No binder is used in the dressing of elements of the same row. Technically, such a wall remains blown through, therefore, it is so important to have facade plastering with a thickness of 30 mm or more or cladding with traditional bricks on cement mortar. Sometimes this rule is deviated from in low-rise construction, and the outer layer of the wall is removed from the insulating blocks with fine masonry. In the absence of insulation between the layers of the wall, from the inside, the gaps between the blocks are filled with polyurethane foam, the consumption of which is minimal due to the precise adjustment of the blocks.
Recommended floor types
Despite its low own weight, it is not recommended to load walls made of porous ceramic blocks with prefabricated and monolithic reinforced concrete floors in buildings more than two stories high. It is much more correct to arrange frame floors on wooden trusses or beams.
There is a myth that a reinforced crown is not required under the ceiling. However, it is still necessary to distribute the load over the spacing of the beams. The crown has a minimum thickness: 12 mm of reinforcement and two protective layers of 30 mm each. In multilayer walls, it is cast on a panel formwork attached from the inside; outside, an insulating masonry acts as a fence.
For single-layer walls, special trays made of warm ceramics are used as a permanent formwork. They not only provide protection for the floor, but also create a uniform surface on the front of the building.