Formwork: important recommendations
- deviation from the planned design should not be more than 2 mm;
- poorly bonded formwork will most likely not withstand the load of the concrete mixture, or in some places will simply move away from the planned shape;
- before mounting the formwork, the surface on which it will be mounted must be leveled;
- fixing the formwork should be carried out using special fasteners;
- the gaps between the shields should not be more than 2 mm.
How to properly reinforce the strip foundation with your own hands
Formwork can be created from almost everything that is available. Most often it is made of wooden shields or ordinary boards. Moreover, the latter can be used both edged and unedged. Recently, plastic formwork is being installed more and more often. It has a low cost. Another option is sheets of moisture resistant or ordinary plywood.
Boards are used to strengthen the entire structure, as well as to connect plywood sheets. Spacers are installed where it is necessary to align a single formwork line. The more such spacers, the better the formwork will withstand the pressure of concrete.
There are only two types of formwork: fixed and removable. The first type can only be used once. After all, after the concrete hardens, the formwork turns into a functional unit of the finished surface.
Formwork of the second type can be used many times, since after the concrete solution has hardened, the formwork is dismantled. As a result, construction work becomes cheaper.
This formwork is prefabricated. As a rule, it consists of polystyrene foam blocks or plates connected by jumpers and having locking grooves. This ensures the reliability of the formwork. The plates themselves are quite light — they weigh no more than 1.5 kg. Their inner surface is porous, which provides better adhesion to concrete.
This is an efficient design that creates the desired shape. As a result, it provides:
- protection against fungus and the environment;
- thermal insulation and waterproofing.
Removable formwork can be assembled from different materials.
- Shields. Such formwork stands out among others with its low cost.
- Plastic. Polymer panels are used for formwork, and sometimes fiberglass is also used. Shields are reinforced with a metal frame.
- Chipboard with metal frame. The material itself makes it easy to choose the right size of the structure.
- Cutting board. From it you can assemble shields of various sizes.
This support system is quite easy to mount. However, it is important to follow the sequence of actions. First you need to mark the place of work, dig a trench or pit to the base of the proposed foundation. Then it is necessary to carry out the final marking and mount the reinforcing cage. After that, you can proceed to the installation of the formwork itself.
Shields of a given size are assembled from plywood or edged boards. Then a layer of polyethylene is attached to the inside of each shield or used machine oil is applied. If this is not done, then during the drying process, the concrete mortar will seize with plywood or boards, and they must be cleaned for reuse.
To maintain the correct geometry of the foundation, it is recommended to pull the cord and install blocks or shields on it.
The walls of the removable structure are fixed with wooden bars. In addition, welding can be used to unfasten the formwork. To do this, depending on the diameter of the reinforcement, parallel holes with a diameter of 8 to 10 mm are drilled in wooden shields. Reinforcement is inserted into them and another piece of reinforcement is welded perpendicular to it, which fits snugly against the formwork shield. Thus, a welded T‑shape should be obtained from different sides of the formwork, which will hold the pressure of the concrete mix.
Concrete from mixers should be poured evenly into the prepared formwork. It is unacceptable to pour it in one place. At the same time, it is necessary to strictly monitor the behavior of the formwork: if you notice that it is bursting, pouring should be stopped, and the site should be strengthened. Dismantling of the formwork is carried out on the second or third day after pouring.
The article was published in the journal “Advice of Professionals” No. 3 (2019). You can subscribe to the printed version of the publication.