Today, all over the world, such a branch of the national economy as construction is developing at a rapid pace. Every year thousands of structures are built, new building materials are introduced into practice, and construction methods are improved. To do this or that job, it is important to build the foundation correctly. This is extremely important for construction. The foundation can be made either with your own hands or with the help of a team of workers. Of course, first of all this concerns private construction. The design of any home involves hydro- and thermal insulation, which provides it with protection from moisture and cold.
The importance of waterproofing for the foundation of a house increases many times over if it is planned to build a usable ground floor or basement.
Waterproofing is included in the design of any building, because the strength of the structure and its durability largely depend on it.
The foundation especially needs waterproofing. It is advisable to do this so that underground and surface waters do not destroy the slab (monolithic) foundation. A monolithic (slab) block has the ability to absorb water, as a result of which a poor-quality base can be obtained. Let's take a closer look at how foundation waterproofing is properly organized; a monolithic slab has its own characteristics in this regard.
Construction of a slab foundation
The construction of a slab foundation involves significant consumption of concrete and reinforcement. Such a foundation is advisable in the case of constructing a compact house or other structure where the construction of a high base is not required and the slab itself is intended to be used as a floor.
If we are talking about building a cottage of a higher class, then foundations are usually built in the form of cross-reinforced strips or ribbed slabs.
What is a monolithic strip foundation
The design of such a base is one-piece, made of steel reinforcing bars and concrete mixture. The monolithic foundation strip is located along the perimeter of the object, under all its load-bearing walls. If the work technology is followed, the structure turns out to be monolithic and is reliable and durable.
It is recommended to install a strip monolithic reinforced concrete foundation when groundwater is deep, when its level is located significantly below the design depth of the reinforced concrete foundation. Otherwise, it is necessary to arrange a drainage system, which requires attracting additional and very substantial funding.
Arrangement of supporting structures
Thanks to the large support area of the slabs, the pressure on the ground is reduced to 0.1 kg/cm2. In this case, cross stiffeners form a structure that is quite resistant to those alternating loads that arise when:
- drawdown,
- freezing,
- soil thawing.
The construction of such structures requires the use of high-strength concrete (class not lower than B12.5) and reinforcing bars with a diameter of at least 12 mm - 16 mm.
The relatively large volume of consumption of concrete and reinforcing steel is fully justified if all other technical solutions for foundations in these conditions cannot confidently guarantee their reliable functioning. In those buildings where the floor is located quite low above the ground level, slab foundations are even more economical than columnar foundations, since there is no need to install a grillage or basement floor.
Stages of work execution
Laying reinforcement for pouring the slab
The first feature of the work being carried out is the correct marking. It is necessary to take into account the possible presence of a terrace, veranda, and any additional premises. A high-quality slab foundation must be monolithic. When carrying out markings, it is important to take into account the supply of communications, and therefore the markings made along the entire perimeter of the building are at least a meter wider in width than its dimensions.- When determining the depth of the slab, the quality of the soil is taken into account. The softer the soil, the deeper the monolithic slab will be laid. This figure can range from 50 centimeters to one meter or a little more. In cases where the pit is dug deeper than required, backfilling is done only with sand to avoid possible shrinkage. At this stage, it is worth taking care of arranging a drainage system to drain excess water, making a slight slope towards the drainage.
- The bottom of the finished pit is covered with sand. The sand cushion is a protective layer that prevents the negative impact on the slab from heaving soil, but equally important is the uniform distribution of the load on the ground, which is the building. It is important that the sand used to create the pillow is clean. The content of chalk, clay or other impurities that cause shrinkage is unacceptable.
The sand layer should be large enough. It does not reach the level of natural soil, that is, the edge of the pit, by no more than 20 centimeters. A significant stage of the work performed is compaction. The sand from which the pillow is made must be carefully compacted, but first take care of connecting all the necessary communications. If the depth of the pit reaches a meter, then the sand should be compacted in layers. The thickness of each layer does not exceed 40 centimeters.
Now it’s the turn to use geotextiles. It is lined over the entire surface and represents a kind of barrier for mixing sand with the subsequent layer of slab “pie”. The permeability of this material allows it to pass water, and a clear boundary between crushed stone and sand will ensure that the house does not deform or sag.
Gravel or crushed stone is laid on top of the geotextile. It is this layer that is responsible for uniform load on the soil and prevents the accumulation of water. Moisture passes through gravel, geotextiles and sand without accumulating under the foundation of the house. At this stage, when spreading gravel, builders will need a level. With its help, you can absolutely accurately mark the horizon during the next compaction. A surface prepared strictly according to the level is also a necessary condition for uniform distribution of the load and the absence of deformation and destruction of the foundation and the house as a whole.
Unburied solid slab
An unburied solid slab as an element of the spatial system “slab-above-foundation structure” allows for the perception of possible soil deformations and external force influences. In this case, it is not necessary to carry out various measures to prevent uneven soil deformations (and in conditions of sandy, heaving and weak soils, significant resources are spent on such measures).
Compared to buried structures, the use of a non-buried foundation slab can reduce labor costs by 40%, concrete consumption by 30%, and the cost of the underground part by 50%. However, in order to protect such slabs from freezing, they must be insulated.
Necessity of application
Slab foundations are one of the most reliable types of house foundations. In this regard, they are superior to tape and columnar ones in any case. However, the area of this type of structure is very large. They are solid foundations - a single thick slab under the entire house.
The construction of such structures is, of course, very expensive. In addition, for example, when building a low-rise country house, foundations of this type, unlike others, cannot be filled with concrete using homemade means. In this case, the cement mortar has to be ordered ready-made. Liquid concrete is poured into the formwork when constructing such a foundation from a tank using a hose. And this, of course, makes the construction of the foundation even more expensive.
Due to the high cost, foundations with a solid slab are built under houses quite rarely. Their construction is considered advisable mainly only when the building is built on non-static soils. In this case, a solid slab can maintain the integrity of other building structures during movements.
Also, foundations of this type can be erected under various types of small-area buildings. For example, sometimes garden gazebos are built on such a foundation. Most often, under such structures, of course, columnar foundations are built. A solid foundation, however, in this case can also be a good solution.
The slab under the gazebo or small extension, of course, will be very small in size. If the concrete depth is shallow, it won’t take much. In addition, it will be possible to fill the slab under the gazebo without the use of special equipment and assistants - manually at a time.
Shallow foundation
In cold regions where there is seasonal freezing of the soil and the possibility of frost heaving, a practical alternative to the more expensive deep foundation is a frost-resistant shallow foundation.
The shallow laying of such foundations is achieved thanks to the installation of thermal insulation placed in the most important places (around the house). As a result, it becomes possible to build foundations with a laying depth of 40 cm - 50 cm (and even in very harsh climates).
Consequences of lack of waterproofing of the foundation slab
Water can have an extremely negative impact on the condition of many building materials, including concrete, which serves as the basis for the foundation slab. Negative consequences are associated with its porous structure, which perfectly absorbs incoming moisture.
Due to the fact that the water penetrating from the soil into the concrete contains impurities of mineral salts, the slab without proper waterproofing is destroyed. The reason for this is the processes of crystallization and increase in the volume of water, the structure is subjected to pressure from the inside, its strength decreases, which can lead to the collapse of the building.
The possible negative impact of water may also be due to the fact that when it gets into concrete, it washes out all the salts and a number of other elements from it. This leads to rapid destruction of the structure. In the absence of high-quality waterproofing of the foundation slab, the walls may begin to draw moisture from the foundation, which causes mold and dampness to appear in the house.
Frost-resistant foundation technology
The technology of frost-resistant shallow foundations is very popular in Scandinavian countries. Such foundations are made in the form of a reinforced concrete monolithic slab 20 cm - 25 cm thick, which has thickened edges, which are contour ribs.
To protect against frost, foam insulation (foam plastic) is used.
The heat that goes through the foundation slab into the ground from the house, plus geothermal heat, causes the freezing line to rise up along the perimeter of the frost-resistant foundation.
Video. Monolithic slab foundation - cushion and formwork
Video. Instructions for constructing a slab foundation using Planter membranes
Articles about the foundation
- Types of foundations
- Wooden column foundation
- Brick columnar foundation
- Columnar foundation made of bored piles
- Columnar foundation
- Screw foundation
- Strip-column foundation
- Influence of soil type on the choice of foundation design
- Choosing material for the foundation of the house
- Construction of a foundation for a stone house
- Construction of a foundation for a frame house
- Construction of a frame house
- back to the section “Building a house with your own hands”
Waterproofing and foundation construction
Laying roll waterproofing
When starting work on installing waterproofing and a slab foundation for a private house, it is important to remember that the formwork is placed strictly along the perimeter of the future house! The markings for the pit were made 1 meter larger. It is this distance that will be needed to arrange the drainage system. The height of the formwork fully corresponds to the thickness of the slab, which will become the foundation of a private house.
Bitumen-based roll materials are used as effective waterproofing. They are laid on top of a gravel cushion, the strips are welded together, not forgetting about the overlap on the formwork. For reinforcement, you will need reinforcement rods with a diameter of 14 millimeters, which are connected to each other. This is how two rows are prepared and they are also tied, providing vertical fastening. The concrete layer should hide the reinforcement, rising above it by at least 5 cm.
When pouring concrete, it is necessary to constantly check the horizon. Only a perfectly flat surface of a monolithic slab can become a reliable foundation for a house.
Methods for processing slab structures
A set of measures for waterproofing the slab base must be provided at the design stage and fully implemented during construction. Waterproofing methods:
- Selecting a brand of concrete with optimal moisture permeability and frost resistance . The first indicator is determined based on the number of storeys of the house, the material of the walls and the method of construction:
- panel and frame houses up to three floors – W4;
houses made of timber on heaving and slightly heaving soils - W4 and W6, respectively;
- brick and monolithic buildings - W8.
- Design solutions that limit direct contact of the slab base with water:
- installation of a drainage system,
replacement of the ground base under the supporting area of the foundation with soil that is not prone to heaving.
- Treatment of surfaces with waterproofing materials - rolls, coating, putty, etc. Affordable and with high hydrophobic properties, modern materials help to implement high-quality waterproofing of slab foundations. The differences between the options are discussed in the next section.
- Installation of “cold” seams . Simultaneous pouring of concrete into a large volume of space can take up to 5 hours. Due to the overlapping of layers, microcracks form in the body of the slab, into which moisture penetrates. To compensate for this circumstance, the joints are designed in advance - they are filled with waterproofing dowel , and then the screed is continued.
For screeding slab foundations, concrete with frost resistance from F35 to F35 is used. In this case, the content of clay particles in the mixture for the solution should not exceed 1%. Internal waterproofing measures may also involve the addition of penetrating (penetrating) compounds with hydrophobic properties into concrete at the stage of making the solution (the features of the waterproofing agent are discussed in the next section).
The design of the drainage system is aimed at collecting and draining melt, rain and groundwater from the building contour. The event is especially effective in areas prone to flooding and in regions with large amounts of precipitation. The drainage system consists of a set of perforated pipes connected to wells or collectors.
Building a slab foundation without excavating a pit and replacing the soil mass with a cushion made of non-metallic materials is allowed only if the work is carried out on sandy or coarse rocks with deep underground sources.
For other types of soil, which make up the predominant part in Russia (80%), under the foundation it is necessary to arrange a backfill that is not prone to heaving and will neutralize the effect of deformation forces on the structure as a result of temperature changes.
