To achieve a concrete structure, intended to undergo masses, pulls or stretching, whether it is a lintel, slab, poles, foundations or window sills, it is most often necessary to reinforce by a metal frame which makes qualify the work of "reinforced concrete". These reinforcements called "concrete bars" are actually long drawn steel rods. It will therefore be necessary to prepare a formwork that will have the dimensions of the structure to be produced as internal measures, then create the reinforcement according to these measurements and finally pour the concrete into the formwork to completely cover this reinforcement.
- Meter and pencil
- Hammer, hammer
- Claw to bend
- Making a formwork
- Realization of the reinforcement
Making a formwork
1. The realization of a formwork is not always obvious. It is often necessary to use ingenuity to obtain the desired result on site, because it is rare to be able to do it in the workshop. It is also a specialized building trade. Rigor in the taking of odds is the first step that must be respected. And stick to it.
2. It is then necessary to always have in mind the forms of the finished work because they are the negative of the formwork to realize. Thus the installation of the inner cleat in this formwork, will make a rebate for the top of the door in the base of the lintel. It is still necessary to be able to evaluate the weight and the thrust of the concrete when it has filled the formwork which will have to seal the material. Finally, once the concrete poured and sufficiently taken, it is necessary to be able to remove the formwork without causing damage to the still fresh work.
3. Depending on the size of the work to be done, do not skimp on the means to strengthen it so that its shape remains stable in all respects. 27 mm thick fir planks are the ideal material for this type of work in range. Planed, they will give smooth faces to the work while, used rough sawn, they will leave on the concrete a footprint more or less marked. Coat their inner faces with form release oil (avoid the oil that drains the concrete).
4. Mount the first vertical plank square to the square of the base plank and nail it without pushing the nails completely except at the most pressure-sensitive places: think of stripping. Continue with meter and pencil, square and level, handsaw, nails, pliers and hammer.
5. Once the formwork is put in place, it may be easier to install the frame and stall it to the standards to be respected before completing the assembly. Namely: there must be a minimum equidistance of 20 mm between the outside of the iron and the inside of the boards of the formwork. It is therefore necessary to wedge the entire reinforcement to this dimension and ensure that it does not move during the filling operation to meet the standards of coating. You can then, and with this condition, finish the formwork assembly to be able to pour the concrete.
6. Fill the form with a shovel or bucket and, without moving the frame, facilitate the trowel distribution of the concrete so as not to create a vacuum and the material adheres well to the trowel. the armature.
7. Finish by striking the side elements of the formwork with a hammer or a heavy hammer in order to bring to the surface, all the air bubbles that the handling of the concrete has enclosed in its mass and which would be as many factors of weakening of his qualities. This operation is called vibrating and is essential.
8. Finish smoothing the concrete at the top edges of the formwork walls with a trowel. It will be necessary to wait several days before removing the formwork because its lower part, suspended in the vacuum, supports a large part of the mass of the concrete which constitutes the lintel.
Realization of the reinforcement
1. The diameter and disposition of the irons vary according to the pieces of concrete to be armed and their destination. For an ordinary post, it is necessary to use irons 8 mm in diameter and also scrape the foot of the post. The reinforcement of a beam or a lintel requires the respect of strict norms, because these pieces are subjected to the stretching: several irons (6) of 16 or 20 mm of section as well as a large number of stirrups ( every 10 cm for example) provide greater resistance. The attachment of a support pole on a beam is provided by irons with curved ends. The reinforcing bars are smooth but more often drawn (a wire is welded on all the way, helically) because they better hang the concrete.
2. The manufacture of a reinforcement is possible in the workshop provided that the exact dimensions of the workpiece (internal dimensions of the formwork) are available. Have a large log attached to a workbench or trestles. The best is to wear on the wood, the design of the hooks according to the received ratings but taking into account and the diameter (thickness of the metal) and the predictable rounding of the angles of folding.
3. Once established on the wood, this plan will give you the exact points of positioning of the studs, bending brackets. Pierce the wood at these precise points and push the studs deeply (heavy-gauge irons can be used).
4. With a claw to bend, begin by bending the end of the iron, the instrument being placed halfway between the end and the angle. Continue the movement until you bend this end and make it parallel to the rod to form an open hook for anchoring irons in concrete and more specifically to the frame of a beam on recessed support. Nails, more easily re-positionable, facilitate the maintenance of the stems.
5. You can achieve the same results with a professional bender, but if you are a beginner, it will not make your job much easier, the helping hand still needs to be acquired. For this reason, it will be beneficial for you to start by simply working a few irons before starting to make a set.
6. The regular installation of stirrups on the rods of the structure is maintained in place by ligatures made with annealed iron wire easy to work. Simply twist it with flat (beginners) or sharp (handyman) pliers. Indeed, with a cutting pliers, the novice handyman will have trouble exerting a pressure only sufficient to keep the wire in its torsion without cutting it before it is completed. The stems cut with sharp cutters such as bolt cutters or disc grinders (possibly with a hacksaw).
7. For some parts whose dimensions may pose a transport problem, it is better to assemble them on site after having delivered the irons and stirrups. Two irons can be assembled in length and ligated together with tight wire provided that the length of the ligature is 40 times the section (diameter) of the irons.
8. In the case of flat structures (slabs), the reinforcement may be in the form of welded mesh which can be cut out. It can also be made with concrete reinforcing bars which will be tied to the crossings to keep them in place. For parts of smaller dimensions (top of sight, small slab), the installation of some irons cut to one of the measures may be sufficient provided that they do not flush the faces of the work.
(photos / visuals: © DIY-Prod, except special mention)
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