- Practical advice
- The realization
- Determine the height of the riser
- Cut the notch
- Center the formwork
- Drill the central chimney
- Insert and fit the tube
- Lighten the riser
- Fill the concrete formwork
- Saw the trash
- Finish the assembly
Any pit, plastic or concrete, has in the upper part a trap door to drain it. An enhancement may be required to access it. When you can not find a perfectly adapted accessory, the easiest way is to make it.
The ventilation outlet is located near the pit, but it can be made to come out elsewhere by an underground sheath.
● Pay attention to the height of the polystyrene blocks, which should not appear on the top
The pit, made of polyethylene, is equipped with a inspection hatch fitted with a single interlocking lid with a cover for a ventilation tube. The set is part of a circular reinforcement that emerges from the ground of a few centimeters. The latter is sloping, the installation of a riser is essential before landscaping.
■ The riser is made from formwork designed to lighten it, giving it an octagonal shape. A string stretched between a high point and a low point of the ground, can determine its height: 20 cm from the reinforcement.
The lid of the lid of the pit is opened with the jigsaw, to ensure the ventilation by means of elbows with 90° and PVC tubes Ø 100 mm. A first elbow is thus oriented towards the inside of the pit. It is extended externally by a section of horizontal tube, a second connection and a vertical tube terminated by a "mushroom" ventilation. The set is assembled with PVC glue, except the first elbow which is just fitted to keep the cover removable.
■ The formwork belt consists of four planks (27 mm thick), nailed to the square to form a frame 80 x 80 cm and 20 cm high. One side is hollowed out with a jigsaw to allow the passage of the horizontal ventilation tube. Four 30 cm long plates, with beveled ends, are arranged symmetrically inside the belt to delimit the octagonal shape and, at the same time, reduce the mass of concrete to be poured.
■ Serving as a circular "chimney", a sixty liter plastic bin is placed, turned over, in the center of the formwork. Previously pierced with an orifice of Ø 100 mm (for ventilation), it fits exactly in the surrounding of the original hatch. Before pouring, four blocks of polystyrene are then placed inside the formwork, as well as an octagonal-shaped Ø 8 mm reinforced iron.
■ The filling is carried out with a concrete dosed with 60 l of sand and 100 l of gravel for 50 kg of cement. Two to three days later, the trash is sawn flush with the concrete and the formwork removed.
■ To close the extension, a striated steel plate is provided with a gripping ring. It is first protected by two layers of antirust, then painted in green garden. Of course, the original cover remains in place, its recess allowing it to be easily released from the ventilation elbow. The land is finally backfilled around the riser before planting or, as here, landscaping that leaves the central hatch accessible.
Determine the height of the riser
To determine the height of the riser, a string is stretched between two pegs located on either side of the pit. The measurement is taken from the edge of the circular reinforcement.
Cut the notch
The original cover has a cover for ventilation. The notch, cut with the jigsaw, corresponds to a passage of Ø 100 mm where will be lodged the first elbow.
Center the formwork
The formwork must be well centered with respect to the outlet of the pit, and set level. Ventilation side, the board was hollowed to allow passage to the horizontal tube of the device.
Drill the central chimney
The plastic bin constituting the central chimney will not be recoverable. As before, it is pierced with a Ø 100 mm hole for the passage of the ventilation tube.
Insert and fit the tube
This tube was removed to position the trash bin in the center of the formwork, by orienting its drilling well. It is then reintroduced and nested in the first elbow coming out of the lid.
Lighten the riser
The oblique plates delimit the octagonal shape. Like polystyrene blocks, they will help to lighten the enhancement. A concrete iron of Ø 8 mm is placed before pouring.
Fill the concrete formwork
The formwork is filled by trowel with a medium-consistency concrete that is vibrated as you tapping the planks with a mallet. It is then carefully smoothed on the surface.
Saw the trash
The concrete must be allowed to run for two to three days before sawing the trash flush with the riser with a fine-toothed hand saw. This allows access to the original cover.
Finish the assembly
The formwork removed, we finish assembling the ventilation device that ends with a special mushroom (Nicoll). The surroundings can then be arranged and the raises closed.