- The main types of formwork for the foundation of the house
- Preparatory earthwork for the installation of the formwork
- Installation of panel formwork for strip foundations
- Installation of permanent formwork with insulation and waterproofing of the foundation
Correctly equipped formwork will allow high-quality filling of the foundation of the house without unnecessary costs and loss of building materials. It is not difficult to build a formwork for the foundation with your own hands, you need to take into account some of the nuances and building codes.
The main types of formwork for the foundation of the house
Formwork is called a panel mold for pouring concrete into the foundation, floors or walls of the house. According to the functional purpose, there are two types of formwork: demountable (removable) and stationary – non-removable.
Removable formwork is made of:
- waterproof sheets of plywood, OSB, chipboard;
- sheets of galvanized metal or corrugated board;
- plastic collapsible structures – industrial production;
- the most inexpensive and popular of boards and materials at hand.
Removable formwork made of moisture-resistant plywood (left) and plastic reusable panels (right)
Prefabricated Metal Foundation Formwork
Removable formwork made of wooden panels
Permanent formwork performs several functions depending on the building material used. It can combine waterproofing, insulation and cladding. The materials used are very diverse:
- glass-cement blocks;
- polystyrene foam finished forms;
- fiberboard, foam concrete and other materials.
The fixed formwork of expanded polystyrene after the foundation is poured will act as thermal insulation
A weighty argument for the arrangement of stationary formwork is not only material savings, but also its useful properties. Thermal insulation will protect the foundation from freezing, and waterproofing from moisture.
Preparatory earthwork for the installation of the formwork
The estimated dimensions of the house in accordance with the drawings are transferred to the prepared land plot. Previously, the fertile soil layer should already be removed on it and the site should be leveled under the entire building spot. The necessary parameters for the foundation trench are marked with pegs and twine.
It is especially important to align the platform for the foundation in level in the horizontal plane
In a trench dug under the foundation, excess soil is removed, the side walls are leveled, and the bottom is compacted and covered with a “pillow” of sand and crushed stone 20–30 cm thick..
At the time of arrangement of the pillow, steel communication “sleeves” are laid at the bottom of the trench. For them, cuttings of pipes with a diameter an order of magnitude larger than the projected pipes of the water supply or sewage disposal are used. If necessary, liners are laid for ventilation of the underground or basement. The diameter of the air vents is from 40 to 100 mm, depending on the area of the house and the parameters of each type of supplied communication.
The usual sand and gravel cushion is being replaced by concrete preparation from construction. The bottom of a trench or foundation pit is compared with a lean concrete screed
The sand-crushed stone “pillow” is covered with a waterproofing layer. For this, roofing material or water-repellent mastics are used. Sometimes insulation material is laid at the bottom of the trench.
Installation of panel formwork for strip foundations
For the most popular strip foundations, formwork panels are hammered from unedged boards with a thickness of 30 mm and a length of 1.5–2 m. The inner side of the panels is made smooth, therefore the stiffeners are attached from the front side of the formwork, and the nails are hammered from the inside and bent outside.
On both sides of the trench, support posts are driven strictly vertically with a step equal to the length of the formwork panel. For racks, a bar with a section of 50×50 mm and more is used. The posts go deep into the ground by 50–70 cm. The first beacon shields are set and attached to the support posts. The center of the support posts vertically is the place where the following shields rally.
During installation, for the reliability of the structure, scrapes are used – longitudinal boards, brackets, tension hooks and tie rods. Every 3-4 m, a transverse tie bar is attached to the upper edge of the shields. Inclined struts are installed on the outside of the boards with a step of 0.5–0.7 m. During the pouring of the concrete foundation, the struts prevent the structure from expanding.
1. Sand pillow. 2. Concrete preparation. 3. Formwork panels. 4. Spacers. 5. Bushing pipe. 6. Support pillars. 7. Cross brace
Vertical bars are stuffed onto the shields, to which wooden spacers are attached at an angle of about 45 °. The lower horizontal bar of the strut rests on the bottom and the vertical wall of the trench for the foundation formwork. During the installation process, the verticality of the installation of the boards is periodically checked with a plumb line and a spirit level.
Do not forget to lay pipes and lintels for entering communications
The last stage of formwork installation is the installation of a reinforcing “skeleton”. The structure is made of thick steel wire or reinforcement 6–12 mm in diameter, depending on the calculated mass of the foundation. Longitudinal metal rods are shifted by transverse cuttings of a rod or reinforcement, tied with a knitting wire or tacked by welding. The size of the cells for the “skeleton” is about 15×15 cm in the horizontal plane and 20×20 cm in the vertical.
After pouring the concrete foundation and drying it, after about 28 days, the formwork is disassembled in the reverse order.
Installation of permanent formwork with insulation and waterproofing of the foundation
Monolithic (non-removable) formwork for the foundation of a house is somewhat easier to install compared to a collapsible panel board. In addition, it is multifunctional and can significantly reduce the cost of waterproofing and insulation of the foundation..
Metal fixed formwork is made of sheet iron with a thickness of 1–2 mm and a profile corner with a shelf width of 4–5 cm. A frame is welded from the corner according to the dimensions of the foundation, onto which a steel sheet is welded. The formwork is treated with anti-corrosion agents and covered with waterproofing bitumen mastic. It is advisable to process the formwork from the outside and inside..
After the installation of the formwork, a reinforcing “skeleton” of wire or reinforcement is mounted in the trench. If necessary, the inner surface is insulated with expanded polystyrene or other suitable insulation. Fixed formwork made of metal will turn out to be durable, resistant to soil subsidence and reliably waterproofing the foundation.
For monolithic formwork made of expanded polystyrene, ready-made forms and components of industrial production are used. The blocks are provided with locks and slots for fastening at a perfectly adjusted right angle. This preparation is not difficult to assemble on your own, and it weighs very little. For additional reinforcement of expanded polystyrene and insulation from the ground, a steel or polymer net, geomembrane or geotextile, wooden or polymer shields are used, which will prevent damage to the insulation layer. After the installation of the polystyrene foam formwork in the trench, soil is poured from the outside and compacted.
Blocks of expanded polystyrene due to the shape and presence of grooves, connecting elements are assembled as a constructor
For permanent formwork made of foam concrete, brick, stone and other similar materials, you need to have masonry skills. A mixture of sand and crushed stone is poured into the bottom of the trench, then it is carefully tamped, and a screed is made over the “pillow” with lean concrete. The formwork blocks are staggered. Particular attention is paid to the correct deduction of corners, verticality of walls and horizontal rows of blocks. For this, every 2-3 rows, the correctness of laying with a plumb line and a long building level is checked.
After the construction and drying of the form under the foundation, waterproofing and insulation are performed on the inside of the permanent formwork. A metal reinforcing “skeleton” is installed, and the formwork is ready for pouring the concrete foundation.
The choice of collapsible (removable) or fixed formwork depends on the expediency of its arrangement and the functional tasks assigned to it.