Monolithic slab under the house

The exit is the same solid slab. Remember the picture from the textbook of physics, where a matchbox swings on the waves, but does not move? The flat foundation will work on the same principle. The soil can raise or lower it, and the house will remain motionless relative to the concrete plane.

These are two exceptional cases in which the use of a monolithic base is economically justified. In any other situation it is better to abandon it in favor of cheaper metal piles or concrete tapes. However, this is only a matter of money – there are no other restrictions. The price of a turnkey foundation, even of a small thickness of 25 cm, starts from 3,600 rubles / m 2. A more powerful plate will pull on 4000-5200. And even the device of a monolithic foundation with its own hands will be only twice cheaper, since the main item of expenditure is the purchase and delivery of building materials. And they just need a lot.

Phased construction technology

If the site just fell under the definition of exceptions or the builder is not so sorry for the money as his own forces, it is time to get acquainted with the monolithic technology and study the manual on the device slab. The step-by-step instruction divides the construction of the foundation into separate stages. Each step is a new layer of a kind of “cake”, and no one can be missed. Works traditionally begin with marking, preparation and leveling of the pit. Building materials will gradually be put in it. Usually, under a shallow-depth slab foundation, it is sufficient to remove the layer of fertile soil and dig a flat platform at a depth of 0.5 to 0.7 m.

Further work order will be as follows:

1. The device drainage pillows.

The first layer of sand is poured, moistened and tamped to a flat surface. Depending on the weight of the future construction (taking into account the basement plate itself), the thickness of the finished cushion is chosen from 20 to 30 cm. Geotextiles are laid from above and re-dumped to a height of 20 cm, but from rubble.

At this stage, you can perform concrete preparation from a liquid solution brand M100. In the presence of a gravel pad, this item is optional, although the cost of pouring is low, but there is a lot of benefit. The thickness of the protective concrete layer is only 1 cm, but provides greater stability of the foundation on the ground and its best protection against excessive moisture. At the same stage, you can take care of the insulation of the monolithic base and partially implement the technology of the Swedish plate. For this, a solid pillow of high-density polystyrene or high density polystyrene is formed over the entire area. But, again, everything is up to the owner.

  Monolithic slab under the house

2. Waterproofing the foundation.

The most inexpensive and important stage of work, after which the monolithic plate acquires “immunity” to the destructive effect of moisture. After all, the non-buried base in any case will be higher than the level of soil freezing, and in winter the absorbed water will begin to tear it from the inside. The inaccessibility of concrete for water will be the key to its long service.

Instructions for waterproofing the foundation recommends starting work with geofabric over the drainage. Its advantage is sometimes called impermeability for cement milk, but in order for it to reach the layer of gravel, the slab would have to be filled with water from a hose.

Truly working legal way of saving.
Everyone needs to know this!

In fact, a dense membrane protects the thin insulation from damage. Two layers of polyethylene film with a thickness of 0.2 mm are placed on the geofabric and the joints are double-welded. Sometimes, ruberoid is used as a hydro-barrier, but its service life is not long enough – in 10 years it will rot, and it will not be replaced. The insulation is taken so wide that at the end of the work the slab foundation can be wrapped from the ends. This creates a continuous waterproof layer that will protect the concrete from moisture and subsequent destruction with the arrival of frost.

3. Installation of formwork and frame.

The slab foundation has a small height – from 15 to 40 cm, so that ordinary boards will be enough for the deck. The main thing is to strengthen them well by placing side mowings and struts, and also to check the parallelism of the opposite walls. The armature is fitted with two horizontal belts with transverse ligation. The cell size is chosen from 200 to 300 mm – this scheme of reinforcement of a monolithic base plate is considered optimal in terms of strength, although it requires a large consumption of rods and knitting wire. The distance from the ends of the rods to the outer walls of the monolith should be about 50 mm. This will provide the metal with reliable protection against corrosion in the body of concrete.

If it is planned to reinforce the foundation with fiberglass reinforcement, the difference can be halved, since the composite is not at all afraid of moisture. The rest of the layout of the rods remains the same. Such a replacement of the traditional metal is done with bars of smaller diameter and provides a good savings, while the strength of the frame is maintained. Plus – the tensile strength of fiberglass reinforcement is much higher than that of the same AIII.

4. Laying concrete.

The entire amount of foundation formwork must be poured in one step. Manually this amount of solution will be difficult to prepare, so it is easier to order its delivery from the nearest RBU. The brand of concrete is selected on the basis of the strength calculation, but usually M250-M350 is enough. The main thing is that the mobility of the mixture was sufficient – class P3 or higher, if the work is performed in hot weather.

The freshly cast monolithic slab is compacted and leveled with vibrating machines or smoothed by a wide rule. The quality of the concrete surface at this stage is of great importance, since the seized mortar is difficult to process. It is better to do everything right away than to grind the cement stone. The plate is covered with a film, but after a day it will have to be moistened. In general, concrete work, it is desirable podgadvat on wet and cloudy weather, so that the hydration proceeded in normal mode.

According to the technology, the monolith should gain strength for 4 weeks, but the demoulding of the foundation can be completed earlier. 70% of the declared grade is enough for the construction to continue – it will reach them already in the second week. So waiting for the full term is optional. After demolding, the left edges of the waterproofing are lifted from the ground and soldered to the ends of the slab.

The technology of the device of the monolithic foundation is indeed the simplest and does not require much experience from builders. That is why it is often chosen by those who are forced to do on their own. After all, with the observance of the instructions, serious errors are practically excluded, and at first no one is considered to be spending.

But on the construction of a monolith can be, and sometimes you need to save. To do this, make a calculation of the thickness of the slab foundation on the basis of the construction scheme. The monolith should be powerful enough to resist bending loads in the gaps between the walls. Partially the “lever arm” can be reduced by forming ribs on the slab.

At the same time, the foundation of too much thickness will not only be material-intensive and expensive, but also increase the pressure on the ground due to its weight. So it is worth spending half an hour of time and independently sorting out the technology of designing reinforced concrete plates.

The foundation in the form of reinforced concrete slabs

When choosing a foundation, they are guided firstly by reliability, secondly by cost. It would be nice if both qualities were combined, but this is not always possible. One of the most reliable bases for building a house is the foundation of a monolithic slab. In some cases, on normal soils for light at home, it is relatively inexpensive, in difficult cases it can be expensive.

Scope and types

Monolithic slab under the house refers to the floating non-buried foundations, it can also be shallow. It got its name due to the fact that the iron-concrete base is poured under the entire area of ​​the house, forming a large slab.

A prerequisite is the presence of sand and gravel cushion, which redistributes the load from the house to the ground, and serves as a damper during frost heaving. Often such a foundation is the only possible solution. For example, on unstable, loose soils or on clays with a great depth of freezing.

The classical warmed plate of the base under the house

The foundation structure of the monolithic slab is simple and reliable, but its production requires a large amount of reinforcement and large volumes of high-grade concrete (not lower than B30), because the entire area occupied by the building is reinforced and concreted, and with a margin for greater stability. Because such a foundation is considered expensive. In principle, this is so, but it must be considered. In some cases, its cost is lower than the tape deep intake – due to the smaller amount of ground work and a smaller amount of concrete.

The depth of the monolithic slab is determined depending on the weight of the house and the type of soil. With a small penetration on heaving soils in winter, the house, together with the foundation, can be raised and lowered. With proper calculation of reinforcement and slab thickness, this does not affect the integrity of the building. The plate compensates for all changes due to the force of elasticity. In the spring, after the ground has melted, the house “sit down” in place.

There are four types of slab foundations:

  • Classical. Reinforced concrete slab is arranged on a sand-gravel pad with insulation or without. The thickness of the concrete layer is 20-50 cm, depending on the soil and the mass of the building. The thickness of the pillow layers depends on the depth of the fertile layer – it must be completely removed. The resulting pit at 2/3 can be filled with sand and gravel.

The classic version of the basement monolithic slab without insulation

  • Insulated Swedish stove (UWB) with built-in underfloor heating. Firstly, it is distinguished by the fact that the slab formwork is fixed – from L-shaped polystyrene foam blocks. This significantly reduces heating costs – heat leakage is minimal. Also, warm floor pipes are laid over the insulation, fittings are placed on them (sometimes under them) and everything is poured with concrete, the thickness of the concrete layer is 10 cm. That is, after the foundation has been fabricated, the heating system is ready and engineering systems have been installed. This approach allows us to speed up the construction, but the foundation itself turns out to be expensive. This type of foundation requires a competent engineering calculation and the same performance: when calculating and laying communications, one cannot be mistaken, since reworking is impossible. Also, there are questions about the repair of systems, immured in the foundation. It is impossible, because they are laying expensive materials with a long warranty.

    USHP – the warmed Swedish plate with the built-in heat-insulated floor

  • Russian – plate with stiffeners. To strengthen the structure for heavy houses and in harsh operating conditions (strong frost swelling), Russian scientists have come up with more stiffening ribs. They are satisfied, as a rule, under the bearing walls. At the same time, the complexity of work increases – stiffening ribs are arranged separately, and a stove separately. But the bearing capacity of such a foundation is much higher, which allows to reduce the thickness of the plate – up to 10-15 cm.

    It looks like a Russian slab foundation in the context

    The structure of the base plate with the edges down and up

    Insulated slab construction technology

    Saving energy becomes a really relevant topic, so very few people build a foundation without insulation. Any slab foundation is a multi-layer construction, and in the case of warming layers even more. To achieve the desired level of quality, you must carefully perform each of the levels. Let us dwell on each in more detail.

    Foundation structure monolithic slab

    Foundation preparation

    The dimensions of the pit under the monolithic slab must be at least 1 meter larger than the building itself. Fertile soil is completely removed on this site. Its thickness in different regions is different – from 20-30 cm to 50 cm and more. In any case, remove all.

    Dig a pit with a margin of 1 meter in all directions

    Along the edge of the pit, just below the general level of the bottom, drainage pipes are laid, which drain the surface water into drainage wells. This measure is necessary so that the walls and the foundation itself do not get wet.

    Complete foundation scheme monolithic slab

    The bottom is leveled, the pits fall asleep, the humps are removed, all are carefully leveled to the level of the horizon and condensed. Geotextiles are rolled to the aligned bottom. It must cover not only the bottom, but also the walls. Cloths are spread out with overlap, the edges are glued together with reinforced tape. Geotextiles prevent the plant roots from germinating, and also prevent the washing out of sand, which serves as a damping pad.

    Bottom leveling

    On the laid geotextiles pour clean sand of medium grain. The layer of sand is 20-30 cm. It is poured in thin layers, evenly distributed and tamped in layers. A layer of sand, which can be tamped with a hand-held vibrating plate, is 8-10 cm. This is how layers of sand are laid. It should also be laid in a level, in the same layer throughout the foundation pit.

    Sand is poured, it must be shed and rammed

    Layer thickness can be controlled with tensioned cords. They are tied to hammered stakes, specially made supports – benches, to the formwork installed in the level (see the photo below). All cords must be in a horizontal plane. Knowing the initial distance from the bottom of the pit to the strained threads, it is possible to determine the height of the poured layer.

    Rubble is poured on tamped sand. Immediately fill up the entire volume, evenly distributing around the site. Aligned rubble rammed to high density.

    Crushed stone filled, installed mortgage elements of sewage and water supply

    At this stage, lay sewer and water pipes. In the already compacted rubble they dig out ditches of the required depth. They should be such that there is some space around the embedded elements. Pipes are laid into the ditches, sand is poured, leveled, the sand is compacted with a shovel or board. More severe compaction can lead to cracks. Therefore, the pipes are laid after tamping.

    Concrete preparation

    Along the perimeter of the pit lay a formwork. It is usually collected from a board 40 mm thick or 18-21 mm plywood. The formwork height for the monolithic slab is the total thickness of the remaining layers. On its edge it is convenient to control the level of concrete when pouring, because the board must be cut. To save material, formwork can be set only for preparation. After the concrete has set, it is dismantled and set up higher, using it again to pour the main slab. But the loss of time with this approach is significant, so it’s not always done so.

    In any case, the formwork is supported from the outside by stops and lugs. The structure must be rigid to withstand the mass of concrete.

    On the tamped gravel pour a layer of concrete 100 mm. This may be a concrete of low marks – B7.5 – B10. Concrete preparation will be a reliable basis for laying waterproofing and insulation, also serves to more evenly distribute the load from the house.

    Poured concrete preparation


    Since the monolithic basement slab is completely in the ground, it needs careful waterproofing. Therefore, two types of materials are commonly used: coating and roll. The base is first thoroughly dedusted, then impregnated with diluted kerosene or solvent primer (and the sides of the concrete preparation are also coated). It is sold very thick and poorly seized with concrete. As a result, the roll-up waterproofing sticks badly and the foundation will get wet. Diluted it becomes more fluid and penetrates deeper into the concrete. At the same time, it almost does not lose its properties.

    When laying out the roll-up waterproofing, it is released outside the basement by 10-15 cm. The sheets of cloth roll out with an overlap, the connecting edges necessarily coat with bitumen mastic and press well. When laying it is necessary to ensure that there are no creases and waves.

    If the groundwater level is high, you may need two layers of roll waterproofing. It is then rolled across, and also glued to the primer (bitumen waterproofing), but you can not dissolve.

    Waterproofing of the monolithic basement slab double – coating and roll

    From rolled waterproofing materials, Hydroisol, TechnoNIKOL Tekhnoelast EPP-4 on high-density polystyrene showed the best. Tehnolnikol of this brand has a high tensile strength of about 60 kg, which increases the chances that it will not be harmed during further work. Use ruberoid, no matter how I want to save, should not be. In the modern version it is too thin and fragile, quickly losing its properties. Replace the waterproofing in the stove, you can not, because lay the best material.

    To reduce the capillary drip of moisture through the slab, you can even use liquid impregnations such as Betonite.It significantly reduces the absorption of moisture. Penetrates to a depth of 50-60 cm, so that the concrete preparation will be impregnated through. The disadvantage of this material is the high price, but the properties of the material are excellent.

    Extrusion of high density extruded polystyrene foam is used to insulate the slab foundation. The thickness of the insulation layer is 10-15 cm, depending on the region (10 cm is enough for an average strip). Laying spend at least two layers, blocking the seams, which form the bridges of cold. It takes more time, but heating costs will be less. If the plates will have an L-shaped lock, they can be put in one layer.

    Since polystyrene foam is “not friendly” with petroleum products, dense polyethylene film is spread on it, and then the insulation material is laid.


    For the reinforcing framework, ribbed reinforcement of class AIII is used, with a diameter of 12-14 mm. It is laid up and down, in increments of 15-30 cm, can have one or two layers. It all depends on the type of soil and the mass of the building. All reinforcement parameters are considered separately.

    From the edge of the slab, the reinforcement should be at a distance of at least 5 cm. Therefore, it fits on special supports that provide the required clearance.

    The first row of reinforcement is connected, some racks are exposed for tying the second belt

    When reinforcing a cage is obtained, in each place of intersection the rods are tied together by a special soft steel wire. There are also connection techniques – using plastic clamps or welding. Tie plastic clips quickly, but not all trust them. Welding is not recommended, because the weld is the most vulnerable place to rust, and the joint is too rigid. When using wire and clamps, the whole structure can “play” a little without destroying the ligament, and during welding such shifts lead to the fact that the seam bursts. As a result, the reliability of such reinforcement is low.

    Filling of a base plate with concrete

    The slab thickness is calculated for each specific case and can be from 20 cm to 50 cm. When casting, use concrete not lower than grade B30. The entire perimeter must be poured in one day, avoiding the appearance of vertical seams. Therefore, for the concreting of the slab foundation, concrete is most often brought ready-made: large volumes are required at a certain time.

    Along with the distribution of concrete, it vibrates

    Schedule of arrival of machines must be calculated so that you have time to distribute the first portion and compact it. For compaction use building vibrators that create high-frequency vibrations. As a result, all the air is removed, the concrete is mixed better, it becomes more fluid and plastic. The result of this treatment is not only a smooth concrete surface, but also a higher hygroscopicity class.

    In the extreme case, you can fill the plate with horizontal layers. Vertical division in this case is unacceptable, since the joints are likely to crack.


    For the normal process of hardening of concrete requires a sufficient level of humidity of 90-100% and temperatures above + 5 ° C. Fill the stove preferably in warm weather with temperatures around + 20 ° C. This temperature mode is optimal for the hardening process. Caring for the monolithic slab concrete is to prevent mechanical damage and maintain moisture.

    Immediately after laying the concrete is closed with a diaper or tarpaulin. It does not allow it to heat up from the sun, the wind does not affect it. The film is glued into large panels. Strip laid with a call at 10-15 cm, taped with tape. It is desirable that the joints be as small as possible, that is, the shelter should consist of one or two pieces, if one is too uncomfortable. In this case, individual pieces of film come one on the other for at least half a meter.

    After casting the monolithic plate is covered with a film

    The dimensions of the film are such that the side surface of the formwork is also closed, and a load can be placed on the edges of the film that will prevent the wind from lifting it. Also, with a load – with boards – they press the place of the prehlest of two panels, in order to reduce the windage, they can be expanded on the surface.

    If the air temperature is above + 5 ° C, approximately 8 hours after pouring, the concrete is watered for the first time. Irrigation should be drip, not jet. In order not to damage the surface with drops, you can lay burlap on it or put a layer of sawdust on it, and close it with a film on top. Water is covered with a covering material, and it maintains the moisture content of the concrete. In any case, watering is carried out only at temperatures above + 5 ° C.

    If there is a threat of freezing, the slab and formwork are also warmed. You can use any insulating materials, both prepared for the construction of the house, and sawdust, straw and other improvised means.

    When to remove the formwork

    For a monolithic slab, it is recommended to remove the formwork after the concrete has gained 70% of the design strength. This period depends on the temperature at which curing takes place. This dependence is shown in the table.

    Table of concrete strength versus temperature

    Differences insulated monolithic Swedish plate and video about its construction

    As it was already said before, the insulated stove designed by Swedish builders for the house is energy saving. At its construction the fixed timbering from extruded expanded polystyrene is used. As a result, heat leakage into the ground is minimal. The second fundamental difference is the system of a water heated floor installed in the slab.

    Since the engineering systems are embedded in the thickness of the concrete, it requires an accurate and competent calculation. High demands are made on execution. Even small mistakes are critical. You can do USP yourself, but the project is better to order. Approximate alignment of costs, see the following photo. The amounts are irrelevant, but the percentage is fair. The cost of the project foundation is about 1%.

    The approximate percentage of the cost of a monolithic slab foundation

    In the following videos you will see the stages of making a Swedish plate for a particular house. Many useful devices have been described that will facilitate the work, explanations on some of the features have been given.

    And look how the Germans poured such a slab. Too many useful nuances.

  • Sources:,, http: //

    Add a Comment

    Your email address will not be published. Required fields are marked *