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Make an insulating concrete slab

The realization of a slab on a dirt floor is quite common, for example in the case of a cellar. The use of vermiculite (expanded mica granules) adds additional insulation qualities to a concrete slab. The realization is consistent with that of a conventional concrete slab: setting up a sub-layer of seat, laying a waterproof film, pouring the slab, then a finishing screed.

Necessary material

  • scantlings
  • Rule
  • Bubble level
  • Hammer
  • Wheelbarrow
  • Shovel
  • Trowel
  • Masonry tank
  • Bucket
  • Float
  • Trowel
  • nails
  • Lime
  • Sand
  • Polyethylene in sheets
  • vermiculite
  • Cement

Steps

  1. Create a sub layer of seat
  2. Pour the insulating slab
  3. Pour the screed

Create a sub layer of seat

The positioning of the bastaings will be corrected by small hammers

The positioning of the bastaings will be corrected by small hammers

1. Begin by roughly leveling the floor and chock two battens in a parallel fashion. Place them on a lime mortar, which you will have prepared beforehand for the later cast bed.Position the two bastaings at the same level, their upper edge corresponding to the final height of the base layer. Adjust this setting by pushing them more or less with small hammer strokes.

Mortar is applied by trowel

Mortar is applied by trowel

2. You can then spread the lime mortar between the bastaings. The distribution is first coarse with a trowel, you will then smooth the seat layer with a ruler long enough, and whose songs will be properly erected. This operation must be done by progressing in short lengths, from the bottom of the room to the front door.

A third bastaing can be used for large spaces

A third bastaing can be used for large spaces

3. Sometimes the room is too large to be treated at one time. If this is the case, place a third bastaing parallel to the first two and operate as before. When this operation is completed, remove the bastaings and reload the spaces left empty in the lime mortar.

Polyethylene sheet is fixed to the wall by nailing

Polyethylene sheet is fixed to the wall by nailing

4. The implementation of lime mortar is facilitated by its fat constitution.
It is then necessary to wait a week at least, or more in winter or in the case of thick layers, before considering the continuation of the operations.
Once the seat layer dries, you can unroll a polyane whose role is to block any rise in moisture. Remember to raise the polyane sheet on the sides, about a height of about 10 cm, and fix it by nailing.
If multiple sheets are needed to cover the piece, overlap them by at least 50 cm.

Pour the insulating slab

The bastaings must be level

The bastaings must be level

5. Place the concrete and vermiculite mixture directly onto the polyane film. In the same spirit as for the layer of seat, arrange bastaings parallel on the ground. Check their level, the thickness of the bastaings corresponding to that of the slab to be cast.

Vermex concrete can be formed on the ground

Vermex concrete can be formed on the ground

6. This insulating slab is obtained by mixing vermiculite with cement. In this case, granules replace the sand and gravel of conventional concretes. The mixture consists of two and a half bags of vermiculite, for a bag of cement and water.
If you work on the ground, form a crater with the granules, then pour the cement, then mix the two components until you obtain a product of homogeneous consistency. Once this mixture is done, reform a crater, pour the water and mix again.

It is also possible to use a concrete mixer

It is also possible to use a concrete mixer

7. The preparation can also be done with a concrete mixer, a solution to remember when the quantities to be prepared are important. You must then pour into the router the different components in the following order: cement, vermiculite and water, in the same proportions as before. Do not make concrete too liquid, which would generate an insufficient level of insulation, or too dry concrete, with the risk of cracks in the drying phase.
Ideally, the speed of rotation of the concrete mixer should be around twenty revolutions per minute.

This solution is faster

This solution is faster

8. With a concrete mixer, mixing is obviously faster and much less tiring. The resulting mixture must then be poured onto a clean surface or into a masonry tank.

Drag a ruler over the bastaings to even out the concrete

Drag a ruler over the bastaings to even out the concrete

9. Spread the concrete with a shovel, between the bastaings set up previously. Equalize the surface of the slab by dragging a ruler on both bastaings, starting from the bottom of the room towards the exit. Drag the bastaings as the progress, reload volumes left empty by their displacement. In this way, cover the entire surface of the room. Then allow to dry a few hours before you can move on the slab.

Pour the screed

Again we use bastaings before applying the mortar

Again we use bastaings before applying the mortar

10. It remains to sink the screed. Made of mortar, it can then receive a floor covering or remain raw, depending on future use.
The stages of realization remain identical in principle to the previous interventions.
Begin by arranging the mortar pads, to stall the bastaings, integrating the thickness of the screed, about 3 cm. This screed must be rich in cement (50 to 60 l of sand per 50 kg of cement), to resist wear, but also moisture.
Provide a mortar that is neither too dry nor too liquid, which in either case would be difficult to equalize.

It is advisable to level the mortar

It is advisable to level the mortar

11. Spread the mortar and level it. You can smooth it gradually with a trowel, finish with a trowel smooth.
Let the screed dry for at least a week before driving on it. During this period, protect it with a plastic sheet, ventilate the room. If the temperature is high, water the screed.

Good smoothness will prevent cracks

Good smoothness will prevent cracks

12. Note that too fast drying can cause cracks in the mortar of the screed.

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