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Insulated plate construction technology
Saving energy is becoming a really hot topic, so few people build a foundation without insulation. Any slab foundation is a multi-layer structure, and in the case of insulation, there are even more layers. To achieve the desired level of quality, it is necessary to carefully perform each of the levels. Let’s dwell on each in more detail.
Substrate preparation
The dimensions of the pit for a monolithic slab should be at least 1 meter larger than the building itself. Fertile soil is completely removed in this area. Its thickness in different regions is different – from 20-30 cm to 50 cm and more. In any case, everything is removed.
Along the edge of the pit, just below the general level of the bottom, drainage pipes are laid, diverting surface water into drainage wells. This measure is necessary so that the walls and the foundation itself do not get wet.
The bottom is leveled, the pits are filled in, the humps are removed, everything is carefully leveled to the level of the horizon and compacted. A geotextile is rolled onto the leveled bottom. It should cover not only the bottom, but also the walls. The canvases are spread with an overlap, the edges are glued together with reinforced tape. Geotextiles prevent plant roots from germinating, and also prevent sand from washing out, which serves as a damper cushion.
Clean sand of medium grain size is poured onto the laid geotextile. Sand layer – 20-30 cm. It is poured in thin layers, evenly distributed and rammed in layers. A layer of sand that can be qualitatively compacted with a manual vibrating plate is 8-10 cm. Sand is laid in such layers. It must also be laid in a level, in an equal layer throughout the pit.
The thickness of the layer can be controlled with stretched cords. They are tied to driven stakes, specially made supports – benches, to the formwork installed in the level (see photo below). All cords must be in a horizontal plane. Knowing the initial distance from the bottom of the pit to the stretched threads, it is possible to determine the height of the poured layer.
Crushed stone is poured on the compacted sand. The entire volume is poured at once, evenly distributing it over the site. Leveled crushed stone is rammed to a high density.
At this stage, sewer and water pipes are laid. Ditches of the required depth are dug in the already compacted rubble. They should be such that there is some space around the embedded elements. Pipes are laid in the ditches, covered with sand, leveled, the sand is compacted with a shovel or board. More severe compaction can lead to cracks. Therefore, the pipes are laid after ramming.
Concrete preparation
Formwork is placed around the perimeter of the pit. It is usually assembled from a board 40 mm thick or plywood 18-21 mm. The formwork height for a monolithic slab is the total thickness of the remaining layers. Along its edge, it is convenient to control the level of concrete during pouring, because the board must be edged. To save material, you can set the formwork only for preparation. After the concrete has set, it is dismantled and put up higher, reused for pouring the main slab. But the loss of time with this approach is significant, so this is not always done.
In any case, the formwork is supported from the outside with stops and jibs. The structure must be rigid to support the mass of concrete.
A layer of concrete 100 mm is poured onto the compacted gravel. It can be concrete of low grades – B7,5 – B10. Concrete preparation will be a reliable basis for laying waterproofing and insulation, and also serves to more evenly distribute the load from the house.
Water proofing
Since the monolithic foundation slab is completely in the ground, it needs careful waterproofing. Therefore, two types of materials are usually used: coating and rolled. The base is first carefully dedusted, then impregnated with diluted kerosene or a primer solvent (and the sides of the concrete preparation are also coated). It is sold very thick and does not adhere well to concrete. As a result, rolled waterproofing does not stick well 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 rolled waterproofing, it is released outside the foundation by 10-15 cm. The panels are rolled out with an overlap, the connecting edges must be smeared with bituminous mastic and pressed well. When laying out, you need to make sure that there are no creases and waves.
If the groundwater level is high, two layers of rolled waterproofing may be needed. It is then rolled across, and also glued onto a primer (bituminous waterproofing), but you can no longer breed it.
Of the rolled waterproofing materials, Hydroizol, TechnoNIKOL Technoelast EPP-4 on high-density polystyrene showed themselves best. Technolnikol of this brand has a high tensile strength of about 60 kg, which increases the chances that it will not be damaged during further work. No matter how much you want to save money, you should not use roofing material. In the modern version, it is too thin and brittle, quickly losing its properties. You cannot replace the waterproofing in the slab, so lay the best material.
It is also possible to reduce the capillary suction of moisture through the slab with the help of liquid impregnations such as Betonite. It greatly reduces the absorption of moisture. It penetrates to a depth of up to 50-60 cm, so that it will saturate the concrete preparation through and through. The disadvantage of this material is the high price, but the properties of the material are excellent.
Warming
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 the Middle Strip). Laying is carried out in at least two layers, overlapping the seams, which form cold bridges. It takes more time, but heating costs will be less. If the plates will have an L-shaped lock, they can be laid in one layer.
Since expanded polystyrene is “not friendly” with petroleum products, a dense plastic film is spread on it, and then heat-insulating material is already laid.
Reinforcement
For the reinforcing frame, class AIII ribbed reinforcement with a diameter of 12-14 mm is used. It is laid up and down, in increments of 15-30 cm, it 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 is placed on special supports that provide the required clearance.
When reinforcing, a cage is obtained, at each intersection the bars are tied together with a special soft steel wire. There are also connection techniques – using plastic clamps or welding. Tie with plastic clamps quickly, but not everyone trusts them. Welding is not recommended, because the weld is the most vulnerable place to rust, and the connection is too rigid. When using wire and clamps, the whole structure can “play” a little without destroying the ligament, and when welding, such movements lead to the seam bursting. As a result, the reliability of such reinforcement is low.
Pouring the foundation slab with concrete
The thickness of the slab is calculated for each specific case and can be from 20 cm to 50 cm. When pouring, concrete of at least grade B30 is used. The entire perimeter must be filled in one day, avoiding the appearance of vertical seams. Therefore, for concreting a slab foundation, most often concrete is brought ready-made: large volumes are required within a certain period.
The schedule for the arrival of the cars must be calculated so that you have time to distribute the first portion and compact it. For compaction, building internal vibrators are used, which create high-frequency vibrations. As a result, all the air is removed, the concrete mixes better, becomes more fluid and plastic. The result of this treatment is not only a smooth concrete surface, but also a higher hygroscopic class.
In extreme cases, you can fill the slab in horizontal layers. Vertical division in this case is unacceptable, since cracks are likely to appear at the joints.
Curing
For a normal concrete hardening process, a sufficient humidity level of 90-100% and a temperature above +5°C is required. It is desirable to pour the stove in warm weather with a temperature of about + 20 ° C. This temperature regime is optimal for the hardening process. Maintenance of monolithic slab concrete consists in preventing mechanical damage and maintaining moisture.
Immediately after laying, the concrete is covered with a diaper or tarpaulin. This does not allow him to heat up from the sun, the wind does not affect him. The film is glued into large panels. The strips are laid with a stop of 10-15 cm, glued with adhesive tape. It is desirable that there are as few unglued joints as possible, that is, the shelter should consist of one or two pieces, if one is too inconvenient. In this case, individual pieces of the film overlap one another by at least half a meter.
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, which will not allow the wind to lift it. Also, with a load – boards – they press the place of overlap of two panels in order to reduce the windage, they can be spread out 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 pour a layer of sawdust, and cover it with a film on top. Covering material is watered, and it maintains the moisture content of concrete. In any case, watering is carried out only at temperatures above + 5 ° C.
If there is a threat of frost, the slab and formwork are additionally insulated. You can use any heat-insulating materials, both prepared for building a house, as well as sawdust, straw and other improvised means.
When to remove 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 hardening occurs. This dependence is shown in the table.
Differences of the insulated monolithic Swedish plate and a video about its construction
As mentioned earlier, the insulated slab under the house developed by Swedish builders is energy-saving. During its construction, fixed formwork made of extruded polystyrene foam is used. As a result, heat leakage into the ground is minimal. The second fundamental difference is the water-heated floor system built into the stove.
Since engineering systems are poured into the thickness of concrete, it requires accurate and competent calculation. High demands are placed on execution. Even small mistakes are critical. You can do UWB yourself, but it is better to order a project. See the next photo for an example cost breakdown. The amounts are no longer relevant, but the percentage is fair. The cost of the foundation project is about 1%.
In the following videos you will see the steps for making a Swedish stove for a specific house. Many useful devices are described that will facilitate the work, explanations are given for some features.
And also look how the Germans pour such a slab. Also a lot of useful nuances.