Contents
Aerated concrete and gas silicate – in fact, the same material – autoclaved cellular concrete. In Russia, blocks are mainly produced on a mixed binder of cement + lime. We practically do not produce pure silicate concretes. Saying “gas silicate”, as a rule, they mean autoclaved aerated concrete.
Cellular concrete has been used for a long time, but with the development of technology, the scope is expanding. If earlier a house of aerated concrete was built infrequently, today this material is already used in 15-20% of new buildings. They build both dachas of temporary residence and capital houses. Everything is explained by the availability of the material at a price, good thermal performance, easy and fast installation.
Foundation for a house made of foam blocks
As you know, foam concrete blocks are lightweight. On the one hand, this is good: it is easier to work and the foundation for such a building is required with a lower bearing capacity, and, therefore, cheaper. But, on the other hand, if there are movements in the foundation, the walls, due to their low weight, cannot “press down” the processes, like a heavier brick, or compensate them like wood. Which means that the requirements for the foundation for an aerated concrete house are increased: even minor miscalculations lead to cracks, which are very expensive to “treat”. Therefore, it is better not to save on the project: it will turn out more expensive.
What type of foundation to use
What kind of foundations are made for a house of aerated concrete. On soils that are not prone to heaving, they usually make a monolithic strip foundation. Depth – below the freezing level of the soil and nothing else. Due to its design, the reinforcement of the tape will compensate for all heaving loads that occur.
If the depth of soil freezing is 2 meters or more, the strip foundation becomes too expensive. In this case, when soils with normal bearing capacity lie at this level, a pile-grillage foundation is made from aerated concrete under the house. In this case, a grillage is indispensable: it compensates for uneven movements that often occur on a pile foundation: one pile has risen more, the other less. Without a grillage, this will lead to cracks, so its device for walls made of this material is mandatory.
The most expensive, but also the most resistant to damage, is the foundation in the form of a monolithic slab. It is placed on soils with low bearing capacity – peat bogs, fine-grained loose sands. It may turn out that it is cheaper than a strip foundation, with a laying depth of more than 2 meters. In this case, the slab is more appropriate if, due to geological features, it is impossible to make a pile foundation.
Prefabricated foundations for this type of material are not recommended. Most of the problems arise with houses made of aerated concrete on foundations made of FBS, building blocks or bricks. Due to the fact that they themselves have a tendency to crack, in tandem with cellular concrete this turns into a serious problem: too many and often cracks occur. Therefore, prefabricated foundations do not use.
And once we pay attention to it, only a designer with the available results of geological research of the site can answer with a 100% guarantee what foundation is needed for a house made of aerated concrete.
With plinth or without
Another feature of aerated concrete is its high hygroscopicity. With increasing humidity, it loses its heat-insulating properties, and prolonged exposure to water can lead to partial destruction of the material. Therefore, a house made of aerated concrete is necessarily placed on the basement, making several layers of cut-off waterproofing. And this is in addition to all measures for waterproofing the foundation, which are also determined by geology and the level of groundwater.
Aerated concrete house: block laying
It all starts with preparations:
- Checking the levelness of the foundation. If there are deviations of more than 30 mm, they must be eliminated. If there are small humps, it is easier to cut them off and fill the holes with mortar. If the surface is too uneven, additional formwork is installed, the surface is poured with concrete and leveled. Just keep in mind that the minimum thickness of the concrete layer is at least 3 cm, and for leveling you need to either add plasticizers that improve spreading, or treat the solution with a concrete vibrator. Work can be continued when the concrete gains 50% strength, which is 7-9 days at a temperature of + 20 ° C, and 14-20 days at lower temperatures.
- Cut-off waterproofing is laid. First, it is smeared with bituminous mastic, rolled waterproofing is rolled on top. And better not ruberoid. It is, of course, cheap, but in the modern version it is ineffective and very short-lived. At the junction of the tapes, one overlaps the other by at least 15 cm.
At the preparatory stage, everything must be done with maximum diligence. The smoother the base, the easier the masonry will go. We have already written about the importance of waterproofing: if you want a house made of aerated concrete to be warm, make sure that it is dry.
Rules for laying aerated concrete blocks
On top of the cut-off waterproofing, laying of aerated concrete can begin. It is carried out according to the same rules as a brick: with a horizontal dressing of the rows. This means that the vertical seam of the lower block is overlapped by the body of the block lying on top. The wall looks more beautiful if the seam is in the middle of the block, but the minimum indent is 10 cm.
For laying gas blocks, special glue is used. That’s what it’s called – for aerated concrete. It is applied in a thin layer of 1-2 mm using a special tool – a carriage with a serrated edge. Why is it desirable to lay such a layer? Firstly, glue is expensive, and secondly, it is a cold bridge, since it has a much higher thermal conductivity than that of a gas block. Therefore, the specified thickness is optimal: it provides a strong docking and minimal heat loss.
Tool
For uniform laying of glue there are branded carriages. They are a box into which is loaded up to a bucket of solution. Do-it-yourself laying of aerated concrete blocks using a carriage is shown in the following video.
Carrying it up and down the walls is a dubious pleasure and is justified only with large volumes, when the entire bucket can be rolled over the wall at a time. Therefore, during the self-construction of an aerated concrete house, simpler devices are often used – small manual carriages (see photo). As you can see, it looks like a scoop and is easy to make with your own hands from a piece of galvanized steel. The width is equal to the width of your block (exactly up to a millimeter, it can be 1-2 mm less). Teeth are cut along the edge (you can use a grinder), a handle is attached. In principle, you can get by with a trowel and a large notched trowel, but it will not work so conveniently.
The second necessary tool is a saw. She also has a special one, but foam concrete is perfectly cut with an ordinary hand saw with a well-sharpened tooth.
Still need a device for shtobleniye. According to the construction technology of aerated concrete, reinforcement is laid in every 4th row. Under these rods, strobes are made in the body of the block. There is a special tool for this – a cutting edge on the handle with an emphasis for the second hand. You can also do something similar yourself.
You also need devices to transfer blocks. There are blocks with cutouts under the arms, but they are more expensive, and then the voids will have to be sealed with mortar. To transfer blocks with even edges, there are special tongs that work due to gravity.
In addition to all this, you need a container for mixing glue, a paint bucket, a mallet – to align the blocks, a brush – to clean off dust, a building level, a cord, a set of skins or a special grater – to level surfaces. That’s all the necessary tool. There is another interesting device – an angle that allows you to cut at a right angle. In the photo it is near the helmet, but if you wish, you can do without it.
Laying aerated concrete block
The technology of laying aerated concrete is simple: glue is applied more or less evenly on the lower surface. The recommended layer thickness is 1-2 mm. With this application using a carriage, there is no excess glue, and it is rarely squeezed out. Glue is also applied to the side surface of the adjacent block. This can be done with a trowel, spatula, or immediately with a carriage. The excess is also removed with the serrated side of the tool. When applying glue, try not to let it flow over the edges of the block: it is difficult to remove it from a white surface.
All of the above applies to laying on a special glue. Some, in order to save money, use a cement-sand mortar. You can’t lay it out in a thin layer, because there will be excess. They are removed with the edge of the tool, but the masonry still looks untidy. It is generally better not to talk about the thermal parameters of such a wall: the cold bridges are very wide.
Before installation, the block is dedusted: they take a brush and walk over all surfaces. If the weather is dry and hot, the block is sprayed with water. You can apply with a wide brush, you can – from a spray bottle. The cleaned and moistened block is lifted and placed on the glue, close to the already installed one. With the help of a mallet, knocking on the clean side surface of the installed block, the required joint thickness of 1,5-3 mm is achieved. Squeezing excess glue is removed with a spatula.
Now we take the level, and level the block in the vertical and horizontal surfaces: we knock on the corresponding places with a mallet. Efforts may be required serious. Extruded glue, if any, we select.
This operation is repeated over and over again. Simple but monotonous work. But you can build a house of aerated concrete with your own hands without any building skills. The main thing is to follow the technology.
Useful devices and useful refinement of masonry technology in the next video. People build a house of aerated concrete for themselves with their own hands, they do everything with high quality, but quickly using interesting devices. The solution is applied using a modified notched trowel. Small plates are attached to it from the sides, they do not allow the solution to drain outside the block. The design is obtained in the form of the letter “P”, but with short “legs” and a wide “back”, a spatula handle sticks out of the middle.
The structure is placed on a block, glue is thrown along the wide side. The edges or the handle are pulled along the block. At the same time, glue is squeezed out from under the teeth. It is immediately distributed evenly. Using the same device, glue is applied to the side, but not of the installed, but of the installed block. The laying speed with this method is high.
Very interesting device for transferring the block. This is a metal bar with two welded handles. Of course, each time it is screwed with two screws to the block, but it is more convenient to carry than just holding the edges. In general, a useful video, they just align the blocks “by eye”. This “technique” is hardly worth adopting, but otherwise the method of laying aerated concrete blocks in the video is very good.
Masonry of the first row of aerated concrete
With any construction, it is very important to correctly set the first row: we will then be guided by it when erecting walls. Therefore, we do everything very carefully, double-checking several times. We put the first row of aerated concrete blocks on a cement-sand mortar, all the rest on glue. Attention! The side surface is coated with glue: these seams should be normal – no more than 1-2 mm.
The corner blocks are laid out first. Very often, their outer edge protrudes beyond the base. Firstly, the base will then be further insulated and finished, and this will significantly increase its thickness. The wall hanging over the basement not only looks more organic, it also reduces the jamming of the basement, and first of all, its junction with the wall, and this is very important for an aerated concrete house.
First of all, using a laser plane builder or a water level, we find the highest corner of the base. We start laying with it. The whole point of the first row is to align the blocks in a horizontal plane by varying the thickness of the solution. At the preparation stage, the largest differences were eliminated, but the surface was still unlikely to become ideal. In order to make it easier to lay aerated concrete blocks in the future, the surface is leveled.
How to find the highest corner of the foundation, see the video.
Therefore, at the highest corner of the solution we put the minimum amount. Spread with a layer of 0,5-1 cm, level. We put the first block so that its outer edges protrude at least 50 cm beyond the base. As they wrote, this protrusion is not necessary, but it solves many problems, and, most importantly, it closes the joint with the base.
We take the level and, tapping with a mallet, align it in the horizontal and vertical planes. On the adjacent corner, we perform the same operation, only the height of the block is adjusted according to the first one, and for this we use the water level. To make it more convenient to work, the level flasks can be fixed on flat boards of the same thickness. By installing one flask on one corner block, the second one can adjust the height of the other.
We repeat the same operation on the remaining blocks. One subtlety: we transfer the level only from the first block. So the error will be less. After all the corner blocks are exposed (they are called lighthouses), a cord is pulled along their outer edge. Moreover, the cord marks the upper edge of the block and all the others are aligned along it. Pull on a self-tapping screw screwed into the block: it spins easily, but it holds up well. It is possible to fasten planks to the blocks into which self-tapping screws are screwed.
It is desirable to lay the masonry from two corners, moving to the middle. So there are more chances to avoid distortions, which then have to be leveled, tearing off already installed blocks.
Second and subsequent rows
Upon completion of laying the row, they take sandpaper, a planer, a building level and pass along the entire perimeter, removing too large height differences. This is an important point that allows you to spend a minimum of glue. But the minimum seam is not everything. If the height of each row is not equalized, places of local stresses form in the wall, which, under minimal loads, can cause cracks. Therefore, do not skip this step.
It is not very convenient to work with emery; there is a special grater for this purpose. She doesn’t clog up like that. So, everything is aligned in the level. Then they take a brush and pass again along the perimeter, sweeping away the dust. This stage also cannot be skipped: the presence of dust significantly reduces the adhesion of the adhesive to the blocks.
All this in order to withstand the recommended adhesive layer of 1-2 mm. The geometry of even the best blocks still has a run-up. Let the difference be 1 mm, but with such an amount of glue it is significant. Therefore, everything is aligned to a complete match.
Hired crews often skip this stage and put glue up to 5 mm or more in violation of the technical process. But such houses turn out to be cold, and the consumption of expensive glue is huge. Average consumption of glue per cube:
- smooth blocks – 1,2 bags;
- with a groove and a ridge – 1 bag.
The laying of the second and subsequent rows of aerated concrete blocks also begins from the corner, only the corner block is set so that the seam is displaced. Now the adhesive composition is applied to all surfaces. The technology of laying aerated concrete block is described above.
Reinforcement of aerated concrete
To increase the degree of resistance of the building to the forces arising from heaving of the soil, longitudinal reinforcement of the walls is carried out. To do this, longitudinal grooves are made in the stacked row of blocks using a special device. For thick outer ones, two grooves are made for two bars; for jumpers up to 200 mm thick, one thread is laid. They should be at least 6 cm from the edge of the block. When chasing two grooves, it is more convenient to maintain a distance by laying the board: one strobe on one side, the second on the other.
When the grooves are ready, dust is swept out of them with a brush. Then they take reinforcement 8 mm, pre-lay out in prepared strobes. They guess so that solid rods lie in the corners: they are simply bent in the right place. The joints of the reinforcement should fall approximately in the middle of the block, but not in the corners of the building and not at the junction of the walls.
One bar is superimposed on another, laying side by side. The overlap should be 10-20 cm. So that the ends of the armatures do not stick out in the places of openings (door and window), small pieces can be bent by making small strobes under them.
When everything is laid out, we take out the bar, moisten the strobe with water and half fill it with glue or concrete mortar. And it is necessary to clean and moisten, otherwise the solution will not adhere to the material of the block and there will be no sense in the reinforcement. We sink the bar into the glue, then we pass the spatula along the grooves, removing the excess and leveling the layer.
Such reinforcement is carried out in the first row, and then in every fourth. With regular bandaging, even with uneven foundation settlement, the aerated concrete house will stand normally.
But this is not all reinforcement. Above the window and door block, as well as in the last row of the floor, more reinforcement elements are required, but already more serious ones, with 4 bars connected into a single system. There are special U-shaped blocks for this. They are placed as the last row under the ceiling of the second floor or under the Mauerlat of the roof. One side wall of the block is thick, the other is thinner. With a thick wall it is deployed and the street, with a thin wall – into the room.
A continuous reinforcing belt is knitted from 4 bars of reinforcement with a diameter of 10-12 mm. It is knitted according to the same principle as in the strip foundation (you can read it here). An example of a reinforcing frame is in the video.
Finished elements are placed in the cavity of the block, poured with concrete grade M200. After concrete has gained 50% strength, floors can be laid or a roof truss system can be installed.
Reinforcement of window openings of aerated concrete houses
According to technology, if a house made of aerated concrete has a window opening wider than 1,8 meters, the penultimate row of gas blocks is additionally reinforced. For this, two longitudinal strobes are made, which are at least 0,5 m longer than the window opening. For reinsurance, you can make more protrusions – up to 1 meter, and reinforce under each window opening.
The technology is similar to the wall one: two strobes into which the bar is placed are filled with glue or mortar. On top of the reinforcement, the last row of blocks is installed, and subsequently a window frame is installed on it.
The general principles of working with foam concrete blocks are described in the following video, and the principles of reinforcing window and door openings are also highlighted
Read about the features of finishing walls made of aerated concrete here.
How to winter without heating
It is often impossible to build a house from aerated concrete in one season, as a result, the box – with or without a roof – goes into the winter without heating. So that after wintering cracks are not found in the walls, a whole range of measures is needed:
- If the groundwater is high, it is necessary to make a drainage system before the onset of cold weather.
- Waterproofing and external insulation of the foundation and plinth (for the middle strip of XPS with a thickness of at least 100 mm).
- Insulated blind area around the house.
- Underfloor heating in the basement.
All these measures are designed to prevent freezing of the soil under the foundation and, in particular, under the basement floor. If the soil under the slab freezes, it will begin to bulge in the most unloaded place – in the middle. If the brick and other heavier materials simply press down on the bulge, then the gas silicate does not have enough mass. Therefore, all of the above measures are required.
In addition to them, in cold weather it is necessary to maintain a positive temperature in the basement – at least to heat a couple of stoves. If there is no way to organize heating, from autumn it is necessary to load fallen leaves into the basement. The layer is preferably large – at least 20 cm. In conjunction with thermal insulation, it will not allow the plate to freeze. Otherwise, it will still bulge, as a result, the walls will crack – under tensile loads, the gas silicate wall cracks not under the seams, like a brick one, but along the “body” of the block. It looks frightening, although with a normal foundation (if it remains intact), everything is not so scary and this may not happen again during heating in all subsequent seasons.