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A reserve for wood, a wine cellar or a workshop accommodate a dirt floor. But to assign a basement to a less restrictive use, impossible to do without hard ground and plan, isolated and concrete.

Pour a slab for a basement

Necessary material

  • Spirit level
  • Laser level or range finder
  • Rule
  • Hand saw with fine teeth
  • grinder
  • Mallet
  • Trowel
  • Shovel
  • Rake
  • Wheelbarrow
  • Hammer hammer
  • Cement mixer

Difficulty: 3/4
Cost: about 1,000 € for 25 m2 (insulation included)
Time: 1 weekend to 4 people

In old houses with a basement, full or not, it is common that the soil is clay. If it is ideal for lovers of good wines, it concentrates a humidity level incompatible with the creation of an additional room, as here a music studio.

Strengthen the feet of walls

The cellars are often low ceiling, it may be necessary to disburse the soil to recover a height of 2.20 m once the development is completed. A solution that may require dig to the foundations and impose their reinforcement reinforced concrete: it is imperative to size well to avoid any further structural disorder, its implementation to be done wall after wall.

An easy complex to make

In a region with mild winters and / or an unheated volume, a simple reinforced concrete slab cast on the ground is then perfectly adequate. On the other hand to make this volume comfortable, the pose of a insulating under slab becomes indispensable. The system chosen here is based on insulating panels in 4 cm thick polyurethane foam (Fitforall Home of Recticel). Other manufacturers offer the same type of solutions (Utherm Floor Unilin, Thin R Xtratherm...). These panels (60 x 120 cm) are characterized by a high compressive strength. Lightweight, they are easily manuportable and accommodate difficult to access places. As for the slab, 7.5 cm thick, it is scrapped and requires a concrete dosed at 350 kg / m3.

Delivery of concrete in a top

Delivery of ready-mixed concrete

Depending on the surface or the situation, it may be interesting to have ready-mixed concrete delivered by a router. Certainly the price is not negligible (120 € / m3 in GSB for example), especially since we must add the cost of the pump if the truck can not park right next to the casting. But in terms of the time / fatigue ratio, this is a solution that must be studied. During the pouring of the concrete, one person spreads it to the rake while another pulls it to the ruler. Nothing to do with a site where one supplies (concrete mixer + wheelbarrow) while the other spreads and stands. And it's even more obvious when the concrete mixer can not be installed near the site and it is necessary to carry buckets...

1. Strengthening the wall feet

Disbanding the soil

  • To obtain a ceiling height of at least 2.20 m, the floor is here disbursed on 50 cm of height at the foot of the walls and 40 cm wide.

Sitting of the walls reinforced by a chaining

  • Exposed, the base of the walls is reinforced by a 15 x 35 cm chaining made with reinforcement cages intersected with the grinder.

Make a formwork

  • Using planks and a few drops of rafters, a formwork is made. He is then rigged carefully.

Wedge the frame

  • A bed of granulate Ø 20-40 mm is deposited on the whole length of the formwork.
  • The frame is then wedged ensuring that it is properly centered in the formwork.

Concrete irons

  • In the corners, Ø 8 mm rebars are bent, and all the steels are bonded with wire.

Laying insulation boards

Fill the concrete formwork

  • The formwork is filled with concrete and the surface erected with a cleat resting on the edge of the formwork.

2. Laying insulation boards

Decline after a week

  • A week of patience is needed before you give up.
  • Concrete will have reached its maximum hardness only after a month.
  • This does not prevent the continuation of the project.
  • To level the ground, to control the level and to fill the gaps with sand.

Install a polyethylene sheet

  • Deploy a sheet of polyethylene as a tarp: in the length of the surface, starting from the middle.
  • Reassemble high enough on the edges (here to the top of the benches).

Install insulation boards

  • Lay a first length of panels.
  • Cut the last to the cutter with the help of a ruler.
  • Reuse the fall at the beginning of the next length.

Lay the cross-joint panels

  • With grooves and tongues, the panels cross-joint.
  • Then cut the edges of the plastic film a few centimeters above the insulation.

Lay a second polyethylene film

  • Once the panels are placed on the entire surface of the room, deploy a second polyethylene film to completely cover the insulating panels.

3. Setting up the reinforcement

Cut out the welded mesh

  • Cut the welded mesh into panels of approximately 2 x 1.20 m.
  • Place them in the length of the room from an angle.

Ligate the trellises

  • The ends of the trellises overlap on 10 to 20 cm (or one-half to one mesh).
  • Ligate them with wire so they stay in position

place the rafters

  • Leave a space of about 8 cm between the rows of trellises to place the rafters that will serve as guides for the ruler.

back up the trellis

  • Cut out 3 cm shims that will allow the trellis to be raised and spread over the entire surface.

the slab must be disconnected

  • Arrange rafters along the edges.
  • Take care to lift the second polyethylene film so that the slab is perfectly separated.

4. Pouring the slab

Pour concrete

  • On this site, to facilitate the descent of concrete poured from the outside, a chute was manufactured, and installed on a stable support (bridge...).

Pour concrete

  • Pouring concrete dosed at 350 kg / m3 starts at the opposite of the chute.
  • Despite the holds, the trellis sinks and deforms when you walk on it...

Pick up the lattice

  • Raise the lattice, by hand or with a rake, to resume its position in the center of the slab.

Build a chute

Brico tip:

  • Reuse the old formwork boards to build a chute to direct concrete into the cellar.
  • A faster solution and less tiring than the use of buckets.

concrete pouring

  • Do not pour concrete over too long (max. 1 m).
  • Position the ruler at the end, then bring it back towards you, resting on the rafters.

Pour concrete

  • Practical, the benches allow here to walk around the slab.
  • In the opposite case, end imperatively by the exit of the room.


  • Chaining reinforcement (15 x 35 cm)
  • Formwork boards and wood chips
  • Concrete irons Ø 6 or 8 mm
  • Polyethylene sheets
  • Insulating panels under slab
  • Welded mesh (20 x 20 cm mesh)
  • Annealed iron wire to be ligated
  • Chevrons 6 x 8 cm thick (or expansion rules)
  • Granulate for Hedgehog Bench (Ø 20-40 mm)
  • Concrete dosed at 350 kg / m3

Video Instruction: Frost Protected Monolithic Slab