Formwork for the foundation: characteristics and features of installation work

Building construction begins with the installation of the foundation, the main element of which is the formwork. In order for the structure to be durable and its design reliably served for many years, it is important to correctly assemble the mold for pouring the armored belt. It is quite possible to do it yourself, but it is important to accurately do all the calculations and adhere to certain technologies.

Formwork is a horizontal or vertical form that is used to fill and screed the foundation of a house. The main components of its device are removable shields and blocks that hold together with the help of special fasteners and fittings. The concrete mixture is poured into the formwork after the reinforcement cage is made, where it hardens and gains strength, then it is dismantled and the subsequent stages of construction are continued. These structures are also used in the case when it is necessary to repair the basement of the building.

In the process of manufacturing the formwork, it is important to ensure that it meets the following requirements:

• was stable, durable and did not deform under the influence of loads;
• had a dense structure without gaps;
• provided high quality surfaces, excluding the appearance of curvature and sagging;
• corresponded to technological characteristics and did not create difficulties when installing fittings and pouring mortar;
• possessed turnover, that is, it was subject to repeated use.

Depending on the design conditions, this design can be combined with several materials at the same time. For example, supporting and bearing elements are made of metal, and those that come into contact with concrete are made of plastic or waterproof plywood.

Today there are many types of formwork, which can be conditionally subdivided into general construction (universal) and a special group designed for the construction of special structures. The most common type of formwork is considered to be collapsible, it is chosen when erecting not only the foundation, but also partitions, walls, beams and columns. For the manufacture of large-sized fragments and bases, as a rule, preference is given to the girder type, and if it is necessary to install buildings of great height with changing geometry, then climbing formwork is used.

In addition, the following types of structures are also used in modern construction:

• Stationary. The formwork is formed from wood and it is excellent for laying a foundation that has non-standard complex shapes. It is simple to assemble the parts of such a device - shields of the required size are knocked down from the boards, fasteners are made and special stops or jumpers are placed for reinforcement.

• Adjustable. It is a universal type of formwork that can be used multiple times. The installation is carried out from steel and outwardly it resembles a constructor assembly. The shields are connected to each other both across and along. The result is a prefabricated structure, twisted with tubes and pins, into the cavity of which concrete is poured.After the initial setting of the mortar, the studs and shields are removed, and the tubes are easily knocked out and can be used for subsequent work. The holes formed from the pipes are covered with cement mortar.
• Suspension. Allows to lay horizontal foundations, intended for staircases and other floors. This is a collapsible formwork, its shields are attached to each other and suspended on beams, thereby limiting the downward movement of concrete.

• Sliding. This design is used in the construction of tall buildings with typical monolithic castings. It can be operated multiple times. The main feature of the device is the presence of a special mechanism, thanks to which it rises on its own.
• Mobile. It can be either a temporary or non-separable design, which has a round, rectangular or square shape. It is considered an indispensable option for concreting long horizontal foundations, since it allows you to simultaneously pour the upper and side parts of the structure. After the mortar has frozen, the formwork is moved to another place using wheel supports or rollers.

Due to its unique structure and special characteristics, it not only provides high-quality concreting of the base, but also reliably protects it from moisture during operation. As a rule, it is erected from wooden panels or ready-made blocks. Depending on whether the formwork is used one-time or multiple times, removable and non-removable types of structures are distinguished.

A distinctive feature of this device is that it is laid with the use of insulating material, so the building turns out to be warm. Permanent formwork is versatile, as it can be used in the construction of private and multi-storey buildings. In addition, it allows you to fill foundations of various shapes with mortar.

The main advantages of such formwork include:

• The speed of the construction process. The assembly of the structure is easy, therefore it shortens the installation time.

• Low temperature resistance. Concrete work during monolithic construction can be carried out at a temperature of -10 C, since the cast frame is additionally insulated.
• Reducing the cost of the foundation and the total weight of the structure. There is no need to hire heavy equipment and craftsmen to lay the foundation.

• High rates of heat and sound insulation of the building.
• The strength of the foundation and the durability of a monolithic structure.
• The ability to install hidden engineering communications. Engineering systems can be mounted directly into the frame and brought out in separate places through holes in the formwork.
• Protection of the structure from natural and biological threats. The building is insect and rodent resistant, mold resistant and does not rot.

As for the disadvantages of this type of formwork, there are few of them:

• The need for external and internal finishing. The only exceptions are structures made of cladding panels.
• Low vapor permeability of heat-insulating material. Therefore, during construction, additional installation of high-quality ventilation of premises is required.
• The building should be grounded, since iron reinforcement is placed inside the walls.

The most popular and widespread type of formwork in construction is considered to be removable. It is made of various materials, depending on the size of the concreted area. Usually, preference is given to moisture-resistant shields, which can be reused. The prefabricated elements of the device are attached to each other using gaskets, bars and ties.The result is a solid and durable structure of any length and shape, which is dismantled at the end of concreting.

Removable models differ in their purpose and can be used not only for laying the foundation, but also for casting individual reinforced concrete elements. On sale are both factory-made formworks and modular or inventory made of metal. They can be used several hundred times in monolithic construction.

The positive characteristics of removable formwork include:

• repeated operation;

• accelerating the pace of construction;
• the ability to erect buildings, of any shape and size, without using additional elements for this;
• easy restoration and repair;
• savings in re-use.

Removable formwork has no disadvantages, the only thing is that this type of structure is not recommended to be purchased for a one-time construction, since its assembly will not be cheap.

Formwork for the foundation can be erected from various materials, the choice of which depends on the complexity of the project and the shape of the base. Usually, wood, metal, reinforced concrete, rubber, reinforced cement and plastic are used for the manufacture of construction panels. The rest of the elements of the device, presented in the form of stiffeners, locks, connecting and fasteners, are made, as a rule, of metal or high-quality plastic.

The most common material for formwork panels are boards, if the structure is small-panel, then it can be assembled from waterproof plywood. It will be cheap, but so that the plywood sheets are not written from contact with the solution, they must be additionally impregnated with a special resin. Plywood formwork allows you to give the concrete surface perfect smoothness, but it is in many ways inferior to plastic and can be used only one time. The wooden structure is assembled from an array with a moisture content of no more than 25%, while conifers are preferred.

To create a structure, it is advisable to choose plates with a thickness of at least 18 mm. In addition, this material will be able to serve in the future as a rough floor. To do this, when laying the foundation, the boards are wrapped with foil, after disassembly they are clean and suitable for flooring.

In the event that it is necessary to translate into reality a project of volumetric monolithic construction, then metal formwork will be the best option for installing the foundation. It is made from 2 mm thick steel sheets and rolled profiles. In this case, the size of the cells in the metal frame should not exceed 5 × 5 mm. The main advantage of a metal device is its ease of installation, durability and the ability to obtain a high-quality concrete surface. The disadvantage of such formwork is the high cost.

In hydraulic engineering, where the laying of large engineering foundations is required, reinforced concrete structures are used. To prevent the concrete pouring from touching the shields, their surface is covered with a special grease and reinforcement is installed. Such formwork makes it possible to lay a solid foundation, but its assembly is expensive.

It is made of dense fabric, and a film is also suitable for these purposes. By heating the air in the shell, the material takes on the desired shape and is attached to the structure using jute fabric, which serves as a reinforcement between the mortar and the device. Then a certain thickness of the solution is poured. Such formwork is inexpensive and has no drawbacks.

Plastic construction is no less popular with craftsmen. It has found application in the laying of both concrete and foam concrete foundations, which are used for the construction of monolithic buildings of various configurations and purposes. In this case, the shields can be assembled from both plastic and polystyrene. Blocks measuring 60 × 30 cm are attached to each other using additional elements in the form of channels, corners and connecting keys. Due to the properties of the material, the formwork is made quickly, and the surface of the base is smooth, does not require finishing, the only thing is that such boards cannot withstand a large weight of concrete.

In addition to the above options, the formwork can also be assembled from profiled sheet and flat slate. In this case, it is best to choose sheets of material with a thickness of 15 to 20 mm and reinforce with wire mesh. Such structures are characterized by high cost and insufficient efficiency, but they are quickly assembled. At the same time, slate formwork has high moisture resistance, is not afraid of temperature changes and has excellent sound insulation. As for the disadvantages, slate weighs a lot and is characterized by low strength.

It performs the role of insulation and cladding, is easy to manufacture, but is designed for laying small foundations. In addition, the foam has a low coefficient of thermal conductivity, therefore, during the construction of the foundation, there is no need to install thermal insulation. Since foam blocks are characterized by a cellular structure, the material is also distinguished by good waterproofing.

To make the foam formwork, they take pairs of plates, fasten them together with metal spacers and the resulting shield is installed in a trench. In some cases, the slabs can be laid out in the form of waves, protrusions or transverse rows. With the help of foam, you can lay a foundation of any kind: from tape to pile-grillage.

The formwork assembly process should start with preliminary design. Therefore, first of all, you need to correctly make the plan and drawing of the foundation, then calculate all the dimensions and determine what the thickness of the fill will be. The foundation markings must be applied prior to the manufacture of the formwork.

To calculate the consumption of wooden boards for the construction of a monolithic base, you must perform the following steps:

• measure the length of the perimeter of the future structure;
• find the required foundation height, taking into account the allowances;
• calculate the thickness of the boards according to the design value.

The length of the building perimeter is multiplied by 2, then the result is multiplied by the height of the foundation and by the thickness of the boards. All calculations should be performed in meters. According to the given parameters, the following calculation is obtained:

(15 + 15 + 9 + 9) x 2 x 0.7 x 0.025 = 1.68 m3.

That is, to assemble the boards, 1.68 m3 of boards will be required. But it is recommended to buy building material with a small margin. In addition to the planks, timber is also needed for the formwork, which will serve as anchorage. As for the calculations for pouring slabs, they are performed knowing the thickness of the slabs and the height of the premises. The consumption of plywood sheets for formwork is calculated based on their dimensions and the area of ​​the foundation. As a rule, plywood with a thickness of at least 18 mm is used for the manufacture of formwork.

The formwork serves as an important element of the foundation, so no construction can do without its installation. Despite the fact that the formwork is characterized by a complex installation technology, it is quite possible to make it with your own hands. It is important during the working process to control the level of accuracy of the placement of the structure in the horizontal and vertical planes. In addition, all calculations should be correctly carried out, since the evenness of the position of the walls of the future building will depend on them.

To build the formwork yourself, you first need to prepare a certain set of tools, since the installation provides for the assembly of panels, reinforcement and concrete pouring. It is also important to decide on whether it will be a removable or non-removable type of formwork. In the first case, the structure is reusable and can be removed after pouring, this must be done when the concrete has set. The second design option is not dismantled, it must be securely fixed with supports and filled with mortar.

Regardless of the design features, the manufacture of formwork consists of the following stages:

• Land preparation. The area where construction is planned is thoroughly cleaned up, especially the area around the dug trench. To avoid overlaps when installing the structure, you will also need to level the soil so that there are no depressions and bumps. A gap of 1–3 cm should be supplied between the formwork and the ground, this will facilitate further installation, and after wedging it will need to be covered with soil. If necessary, a reinforcing mesh is laid on the bottom of the pit or trench, thanks to which the strength of the foundation will increase.

• Making shields. It is possible to assemble the formwork from various materials, but most often wooden boards and bars are chosen for this. The boards must be cut in advance to the desired length, at least 3 m. They are knocked together using transverse segments, observing a step of 1 m.Thus, the assembly of one three-meter shield will require about three knocked-down fragments connected by bars. The difference between the length and height of the device will allow you to conveniently "drive" shields along the entire perimeter of the dug trench.

As for the fastening of the boards to each other, then it can be done with anything: nails or self-tapping screws. The choice is determined by price, reliability and speed of operation. If the boards are fixed on nails, then it should be provided that their caps are placed on the side of the solution.

• Installation of clamps. After the shields are ready and driven along the entire perimeter of the trench, they proceed to the manufacture of wooden clamps. Their length, as a rule, should be at least the height of the shields. Since the clamps play an important role of structural elements and are responsible for additional rigid formwork when it is poured with concrete, they are placed in the middle of the panels between the strips. In addition to the clamps, in the places where the boards are connected, support struts are additionally placed.

From the inside of the structure and from above, you need to fix it with struts. It is important to pay attention to the fact that the formwork is solid and has no cracks, otherwise the solution will leak and the work will be ruined. In the event that there are minor gaps in the structure, then they can be easily sealed with waterproofing materials.

• Laying waterproofing. The inner part of the formwork is covered with dense roofing material and reinforcement is performed. Optionally, the underground part of the foundation can be insulated with expanded polystyrene plates. They are best placed on the outside of the foundation.
• Installation of communication systems. This should be done before pouring concrete.

For information on how to make formwork for the foundation, see the video.