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Pour a mortar screed on a concrete slab

Thick layer of mortar a few centimeters, a screed is casting on a concrete slab to provide a stable and smooth support for laying tiles.
Warning! the mortar being a heavy material, make sure the floor is able to support the weight of the screed.
Particular cases, underfloor heating systems: they include heating frames according to various processes enacted by the standards concerning the power supply, the insulation. The drying times of the screed may in particular be lengthened.
But we are talking here only about a single screed, "pulled" on an existing slab, to put a coating such as tiling.

Necessary material

  • Bubble level
  • Plank of wood
  • Shovel
  • Float
  • Trowel
  • Bastaings well trained
  • Cement and sand or mortar

Steps

  1. Place bastaings, spread mortar
  2. Remove the bastaings and let the screed dry

Place bastaings, spread mortar

Arrangement of bastaings

Arrangement of bastaings

1. For make a screed, first determine the level of the finished screed based on the floor of the next room. Take into account the thickness of the tiles to be laid so that the two coatings are on the same plane. Set the level of battens stalling them with mortar pads. Place a bubble level on a long straight wooden ruler to avoid the risk of error. Two parallel bastaings of the same level are enough for a small room. When working alone, do not remove them by more than 1 or 2 m.

Dusting cement

Dusting cement

2. The screed must adhere firmly to the existing floor. Wet the entire surface of the slab thoroughly and sprinkle it with cement after having dusted it well. Spread the mixture on the floor using an old broom. Calculate the quantity of mortar required depending on the surface of the room and the thickness of the screed (about 5 cm).

Adjustment of the mortar screed

Adjustment of the mortar screed

3. Strike the mortar on a clean surface. Make sure that the mixture does not become too liquid: it would be difficult to work.
Spread the mortar over the entire width of the room. Use a board with perfectly straight edges as a mason's rule to sink (or "pull") the screed by sliding it over the bastaings and thus scrape the excess concrete.

Trowel clogging

Trowel clogging

4. With a trowel, reload the troughs and re-erect with the ruler. There must be no gaps in the walls. Continue spreading the mortar over the entire surface.
Important: The screed must be erected at one time.
Equalize with the trowel to obtain a flat cap. With a trowel smooth perform the surface finish.

Remove the bastaings and let the screed dry

Removing bastaings

Removing bastaings

5. The mortar begins to take two to three hours later. You can then remove the bastaings. To avoid stepping on the cool screed, use thick and wide planks, particle boards or walk in the furrows of the bastaings.

Smoothing with a trowel

Smoothing with a trowel

6. With a trowel, refill the furrows with the mortar. With the trowel and trowel smooth the screed. Proceed backwards to finish near the door. For the screed to dry, it takes about 1 week per centimeter of mortar thickness. The room must be well ventilated during this period. If it is very hot, water the screed every 48 hours or cover the surface with a plastic sheet to prevent the mortar drying too quickly.

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