To open the facade or the gable of a house is a delicate operation, because one intervenes on bearing walls. These works are conditioned by rules of lift, resistance of materials and load transfer. Except to properly master the subject, do not venture alone on such a project, surround yourself with specialists (mason, design office, architect...) who will advise you to avoid errors that can have serious consequences.
- Rafters, shuttering boards (27 mm)
- Formwork oil
- Tracer cord
- Bubble level
- Candles or rafters
- Cement bucket
- Concrete irons
- Practical tip
- Chest the lintel
- Chest the jamb
- Complete the training
The opening of a window or a door modifies the appearance of a facade, and requires an administrative authorization: authorization of work or building permit according to the case.
Drill and lay the props
1. The opening of a window or a door modifies the appearance of a facade, and requires an administrative authorization: authorization of work or building permit according to the case. In addition, it is essential to take the advice of an architect or a person skilled in the art who will appreciate the lift and pushes on this wall.
2. Using a chalk line, mark on the wall the right of way for the opening. Intervene firstly from above, and if possible from the inside to the outside: the rubble is easier to recover, the dust less present inside. An electric drill facilitates work, but causes significant vibrations, which can be harmful with old masonry.
3. In order to support the masonry section above the opening, you can use wooden props or adjustable metal props. This pair of props consists of wooden rafters that support the lintel formwork. Position the struts in place vertically, and adjust with the bubble level the horizontality of the base board of the formwork. In the upper part, the half-row of bricks has been deposited, to provide in the upper part an opening sufficient to pour the concrete.
4. Place the first vertical board squarely. Nail it without squeezing the nails, to facilitate the subsequent stripping. Depending on the desired aspect, you can plane the inside of the shuttering boards to obtain a smooth appearance, or on the contrary leave them rough if you want to print the veins of the wood on the concrete. Finally, consider applying formwork oil on the inside faces of the planks. Do not use drain oil that stains concrete.
Chest the lintel
5. Make the reinforcement that will be used to arm the lintel. Do not forget to take into account the coating, that is to say the 20 mm that must separate it from all parts of the formwork. Refer to the "Concrete reinforcement" sheet.
6. Once the reinforcement is assembled, position it in the formwork and hang it so that it is always at least 20 mm away from the walls of the formwork.
7. Place at the square and nail the second vertical board. Use clamps to maintain the outside spacing, as well as small cleats cut to the inside width, to join and hold the two vertical boards. Finally, you will have to reinforce the center of the formwork by installing a candle in the middle. This candle will prevent the formwork from sagging under the weight of the concrete.
8. Fill the formwork with concrete, pouring it through the top left open. The concrete must be spread as filling progresses, in order to properly coat the reinforcement. Note the use of an inclined board, which allows the concrete to slip more easily and avoid spreading outside the formwork. The concrete will consist of CEM 1 cement (high strength). Choose sufficiently fine aggregates to facilitate the embedding of the reinforcements. The concrete must be dosed for 1 m3, 450 liters of sand, 750 liters of chippings and 400 kg of cement.
9. Once the formwork is filled with concrete, vibrate by tapping the walls with a mallet. By this action, the liquid mass settles, releases any air bubbles and optimizes the coating of the reinforcements.
Chest the jamb
10. Once the concrete has hardened, loosen the lintel. Then proceed to the realization of the window support (Consult the sheet "masonry window support").
11. It is now necessary to form the jamb with two planks erected vertically, and held together with large clamps. In case the demolition has left too much space to reach the vertical, you can fill this void with some bricks or roughly bricked stones. You will then have to trowel a mortar gobetis all the way through the wall.
Complete the training
12. Finalize the dressing with a mortar coating, which is easier to trowel than the trowel because of the clamps that hold the formwork.
13. Smooth the mortar with the trowel.
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