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How to properly pour a slab under the foundation

Advantages and appropriateness of application

Pouring the board directly at the site of the future house allows you to save on shipping and assembling the structure, but the use of solid technology is conditioned by ordering special equipment (auto concrete mixer) and the construction of a drainage trough.

With minimal preparatory activities and following the instructions for erection, the entire installation procedure can be implemented in a few days by your own hands.

The slab foundation is most suitable for unstable and heaving soils

  • moderate ease of construction;
  • practicality and reliability of the basement functioning;
  • Stability against seasonal fluctuations of the soil;
  • the possibility of making a basement, insulated and protected from moisture;
  • considerable period of operation.

The only disadvantage of the plate foundation of the house is its high cost. However, the high cost of the material is more than offset by the guarantee of reliability and safety in the face of damaging environmental factors.

How to properly pour a foundation

Concrete slab casting should be done in one go. But some builders still do the pouring in several stages. You can pour the entire basement, but only half of it. Need to create vertical partitions, and then make the pouring of half, but be sure to the full height of the formwork.

Professionals believe that the pouring needs a sloping joint, it is necessary to make a corner partition. Although official sources can’t give you a definitive answer. Most builders do not think it is right to do the pouring in parts. But that doesn’t mean that if you decide to build a foundation yourself, you can’t pour it in parts. For low-rise houses, this method is perfect, it does not require special stability of the base.

You should not make horizontal joints near horizontal reinforcements. It is ideal if the metal is in one layer and not at a joint. If you pour in small areas, then make vertical joints.

Pouring the foundation slab, how to pour, how to properly pour, the cost of LLC Project

The foundation is the most important element of any building, whether it’s a small commercial pavilion or a high-rise skyscraper. And any miscalculation or desire to save on costs can have very unfortunate consequences for the entire building.

The slab foundation is categorized as a non-deposited or shallow-deposited strip foundation. In essence, it is a reinforced concrete grid or monolithic slab with a thickness of 20 to 50 cm, located under the entire area of the building. It is laid on a 30-40 cm layer of densely rammed sand (or sand, mixed with crushed stone), and the latter, in turn, is located on a smoothed solid ground (not dug and not loosened).

Tips For Pouring A Large Concrete Slab Foundation

The foundation slab can be either a solid monolithic slab, or prefabricated from concrete blocks or building slabs, on top of which a cement screed is made to fill all the gaps and level the surface. The solid monolithic construction is considered the most reliable, because it has a higher spatial stiffness and is much more durable in operation. Yes, and the cost of pouring the foundation slab directly on the construction site will be much less than the purchase, delivery and installation of ready-mixed concrete products by crane. over, you will still need to do the screed on top of them.

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Types and characteristics of a monolithic foundation

Choosing the type of monolithic foundation of the plate type depends on a number of factors:

  • The location of the surface of the slab relative to the zero mark;
  • the method of construction of the foundation structure;
  • constructive variant.

According to the magnitude of deepening into the soil, slab foundations are classified as follows:

  • foundations that are not embedded. They are built on the planned surface of the soil, from which construction debris and vegetation have been removed;
  • shallow foundations. The technology of construction of the foundation slab provides for its immersion into the ground 40-50 cm below the zero mark;
  • buried bases. The lower plane of the reinforced concrete foundation slab is located at or below the depth of the ground freezing.
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The method of arrangement of a solid slab also differs:

  • The monolithic structure is built on a planned and cleaned site. The technology involves the construction of the bed, installation of the formwork, waterproofing, reinforcement and concreting. No lifting equipment is required to build the one-piece slab. Engineering networks and necessary utilities are placed inside the concrete base. The dimensions of the foundation platform are not limited;
  • The precast version is built from standard slabs manufactured in industrial conditions. Laying of the panels is carried out on the crushed stone and sand pad using a crane. After the completion of installation operations, the butt joints are filled with mortar. Allowed to reinforce the precast platform with subsequent casting of the screed layer. Thickness and dimensions of the precast structure are regulated by the dimensions of the finished panels.

The following slabs, differing in design features, shall be constructed:

  • Bowl-shaped platform. It represents a complex design that allows you to build a spacious basement under the house;
  • flat foundation. It is made in the form of a conventional slab, which is additionally insulated with thermal insulator sheet.

Let’s dwell on the characteristics of the solid foundation slab, which is distinguished by the following properties:

  • increased load capacity. Strong structure of reinforced concrete slab does not collapse, taking the weight of the structure and the reaction of the soil;
  • increased moisture resistance. Properly constructed monolithic base does not allow moisture to penetrate through the foundation to the walls;
  • long lifetime. Concrete platform ensures the stability of buildings over a long period of time.

The dimensions of the slab are made in accordance with the dimensions of the structure to be erected, and the thickness depends on certain conditions:

  • the stability of buildings on normal soils is provided with a platform thickness of 40-50 cm;
  • For the reliability of the buildings built on problematic soil, it is necessary to increase the thickness up to 100 cm.

The performance of the monolithic platform is also determined by the brand of concrete mortar, the diameter of reinforcing bars and the design version of the slab.

According to the size of the building being erected, the dimensions of the stove

Professional builders and private developers are convinced of the numerous advantages of monolithic construction:

  • constructive simplicity. The configuration of the foundation follows the contour of the building. The construction of the monolithic platform is carried out in a limited period of time;
  • economical construction. As a result of the construction of a solid slab eliminates the need to arrange the floor. This allows you to save money;
  • increased strength. Due to the use of concrete and properly chosen diameter of the armature, slab foundation prevents the deformation of the walls;
  • versatility. Monolithic foundation is used for different types of buildings, provides durability on movable, wet and freezing grounds;
  • frost resistance. Solid construction of the reinforced concrete slab does not crack as a result of seasonal temperature fluctuations, causing ground movements.

Along with the advantages, the design also has weaknesses:

  • The complexity of constructing a solid slab in sloping terrain;
  • increased costs and increased labor intensity of the work;
  • the necessity to perform additional volumes of excavation work for a sunk foundation.

Disadvantages do not stop builders, who confidently choose a slab foundation for the construction of houses on various types of soil.

Advantages and disadvantages

Pouring the slab on a strip foundation is a traditional solution, which has many advantages. However, such a project requires considerable financial investment. To reduce costs without sacrificing the performance and durability of the foundation, builders began to use monolithic cup-shaped structures, which are installed upside down on the stiffening ribs.

  • Increased strength. It ensures reliable stability and immobility of load-bearing walls.
  • Reduced consumption due to the lack of unnecessary material consumption.
  • A wide range of tape options that allow you to find a quality solution for different conditions.
  • Possibility to arrange the basement.
  • Compatible with various types of soil, including low-soil.
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Another advantage of the strip base should include the simplicity of installation and high speed of execution of works. But, in addition to the advantages, the technology has significant disadvantages. These include a number of difficulties when installing nodes of engineering systems, so there is a need to organize additional space for their installation.

To eliminate the problem, you can use the option of redundant sewer and water systems, which are installed directly under the slab and are used in case of clogging of the main water supply.

Advantages and characteristics of monolithic slabs

Solid reinforced concrete slabs are widely used in the construction of building foundations due to a set of advantages:

  • simple design. One-piece reinforced concrete base is placed over the entire area of the building at ground level or with a slight lowering into the ground. Does not require an increased amount of excavation work, is performed within a limited time;
  • affordable costs. Lower estimated cost of concreting is achieved through the delivery of large volumes of concrete from transport vehicles using troughs. In this case for tying reinforcement, pouring and vibration compaction of concrete using the labor of unskilled workers;
  • increased load-bearing capacity. Increased footprint and rigid spatial reinforcement cage allows for maximum loading of monolithic foundation slab. The design ensures the stability of the erected building during soil movements;
  • Integrity of the building walls. Monolithic platform under the house is not subject to local deformations, evenly transfers the weight of the structure on the ground, compensates for soil swelling in winter;
  • Integration of the building basis with the subfloor. The monolithic foundation acts as a subfloor. It allows you to arrange the floor of the ground floor without using reinforced concrete slabs and pouring screed for the floor covering;

Before starting work, the ground is analyzed

  • The possibility of constructing a slab base on difficult soils. No need for deepening into the ground reduces the labor intensity of excavation activities in areas with close aquifers, as well as in areas of deep freezing of the soil;
  • versatility. The full foundation slab can be used for lightweight buildings, as well as in buildings with heavy walls of brick or concrete blocks.

Along with the advantages the plate design has a number of disadvantages:

  • Problematic conditions on sloping areas with high probability of soil displacement. The problem is solved by pouring monolithic with the base of the ribs at the bottom of the sloping section, which fix the site.
  • Increased estimated cost associated with the involvement of construction firms on a contract basis. Self-construction allows you to significantly reduce costs.
  • Increased excavation and concreting when building a basement. This is due to the need to pour the concrete base below the zero mark at the bottom of the pit.

Concrete Slab Foundation. Process & Best Practices

Peculiarities of a slab base are related to the different location of the site relative to the zero mark. One-piece foundation can be performed:

The standard monolithic slab is mostly demanded in constructions with a basement room

  • shallow. The base of the building is immersed in the soil to a depth of 30-40 cm until the supporting surface coincides with the zero mark;
  • buried. It is used in the construction of buildings with basement and basement rooms. Construction is associated with a significant amount of excavation work, a sharp increase in costs.

The slab foundation differs in design and method of formation:

  • Monolithic is poured into the formwork with the installed reinforcing cage. The entire structure is cast in one step, forming a solid foundation. The construction is characterized by high strength.
  • Prefabricated consists of individual reinforced concrete slabs, which are laid on a macadam cushion. The gaps between them are concreted, and the surface is leveled with a small layer of mortar. The prefabricated variant of the foundation loses to the monolithic one in terms of strength characteristics.

For the construction of a solid foundation is required:

  • Apply high-quality steel reinforcement;
  • Follow the recipe in the manufacture of concrete mortar;
  • Adhere to the technology of performing work.

A stronger base is the slab, which has stiffening ribs

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Compliance with these requirements will form a solid base of the building, avoiding the appearance of cracks in the walls.

Concrete mix placement into the formwork

Before filling the formwork, you need to properly prepare concrete or order delivery by mixer trucks from a reliable manufacturer. For a monolithic foundation slab, the concrete mixture must meet the following parameters:

For these purposes, commercial concrete with the characteristics of 196 kg/cm², W4, F100, P3 is excellent. It has sufficient mobility for distribution in the formwork, can withstand 100 seasonal cycles, does not leak water at a pressure of 4 bar.

During freezing the water droplets inside the mixture increase by 9%, internal stresses exceed the strength of the slab many times. The frost resistance of the material is wholly dependent on the presence of reserve pores in the concrete structure. When freezing, some of the moisture fills them, preventing cracking.

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When making the mixture with your own hands it is therefore necessary to ensure a freeze-thaw resistance of F75. F150 for regions with winter temperatures below.2040 degrees, respectively. These conditions correspond to the technology of preparing ready-mixed concrete BGS B20 (M250), BGS B15 (M200). For economical consumption of cement, taking into account ground conditions, construction technology should be chosen:

  • M350. M400. for monolithic, brick buildings on the swelling, weak swelling soils, respectively;
  • M300. M350. for buildings of expanded clay, foam and gas concrete;
  • M250. M300. for log, log cabins;
  • M200. M250. for panel and frame houses.

For concrete preparation (unreinforced bed under the slab), the recommended proportions are 6/3/1 (crushed stone, sand, cement, respectively). For pouring the slab the proportions change 3/1,5/1.

Before placing the concrete in the formwork, the reinforcement must not have flaking rust, dirt, oil stains.

The poured foundations. How to pour a foundation slab

The strip foundation is classified as a class of below-ground or below-grade foundations. It is a reinforced concrete slab, laid on a layer of well-compacted crushed stone or sand, 10-30 cm thick, under which is the leveled continental soil (not dug, not loosened earth).

The thickness of reinforced concrete slabs is usually 20-40 cm. You can use both monolithic slab, which is erected on site, and precast concrete, such as: road slabs. In this case the slab is levelled with cement mortar or normal concrete on top of the slab. Undoubtedly, the monolithic slab foundation has great spatial stiffness and is more reliable and durable in operation than a precast slab foundation. In this case the concreting of slab foundations on site can be cheaper than the purchase, delivery and installation by crane of road plates. This is all the more so since they still have to be “covered” with a cement mortar screed.

Features of the marking of slab foundation

Marking. not complicated, but very important stage of construction. Without accurate marking, further construction of the house can turn into sheer misery and trouble with not only the foundation itself, but also the walls and the roof.

How to accurately make a markup of the foundation for the house with their own hands. I described in a previous article, we will not dwell on this. Consider only some minor differences:

  • For a slab foundation, the marking is made much easier, because it is enough to mark only the perimeter of the house. And where the internal walls and partitions will be located, you can decide already on the ready-made foundation.
  • The slab foundation is marked, on each side, one meter wider than the perimeter of the house. This is necessary in order to make the drainage system and backsplash.
  • As a rule, if the house has terraces, balconies, porches or extensions, they are also marked and poured together with the main foundation, because the slab foundation must be monolithic. Otherwise, the integrity of the walls of your future home, no one can guarantee.
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Author

Kerariel

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