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Make a mortar bonded with cement to plaster

Covering a rough wall (brick, stone or concrete) with a plaster, will provide a smooth surface able to receive a plaster (outside) or a coating (indoors). Whatever the wall, for coat a wallyou will always start by troweling a bottom coating, called "gobetis", which serves as an underlay for the main plaster ("plaster body"). It will be placed once the gobetis dry. On a facade, we can also apply a finishing coat and, finally, a speckled plaster on the zip line.

Necessary material

  • Brush
  • Rule
  • Plumb-line
  • Plasterer's trowel
  • Plaster trough
  • Float
  • Sponge
  • Plaster
  • Wood wedges
  • Bubble level

Steps

  1. Cleaning and humidifying the wall
  2. Preparation of the surface to be coated
  3. Application of the mortar coating
  4. Smoothing of the plaster and projection of plaster

Cleaning and humidifying the wall

Brushing the wall

Brushing the wall

1. The realization of a wall coating begins with the preparation of its support. Even new, it is never in perfect condition before being covered by a layer of plaster. After possible repair of the structural work, the surface must be clean and healthy. Brush off any dust and dirt that may be present. As in the case of a surface to be painted, a dirty support impedes the attachment of the coating. In this case, the degradation is late but inescapable.

Sprinkling of the wall

Sprinkling of the wall

2. Most often, the structure to be covered is made of porous materials. For its preparation, the coating has a large amount of water, greater than that required for crystallization drying. A porous support, absorbing a large part of the water of the coating, risks depriving it of a correct grip. This is the danger of pumping the shell work by capillarity. It is essential to wet the support before coating; abundantly in the case of blocks, rough concrete or hollow bricks.

Projection of gobetis

Projection of gobetis

3. Prepare a clear, that is to say very diluted plaster: project it on the wet wall of the back of the trowel. This gobetis, undercoat with the final coating, plays an important role. Its fluidity allows the first imbrication of a material in the other. The rough substrate has as many particle traps as cavities; these asperities play the role of crampons and solidarize the shell and the coat of plaster.

Preparation of the surface to be coated

The shell is never perfectly flat nor vertical. It is difficult to catch and rectify these anomalies by passing the coating layer intuitively. The coating corrects the imperfections of the support. The thickness of the plaster is in a range of 1 to 2 cm, otherwise it comes off ineluctably...

Rule check

Rule check

4. Arrange wood shims or thick marks on the shell whose face will indicate the final surface of thewall coating. Check their alignment and verticality with a large straight or perfectly straight aluminum ruler.

Plumb line control

Plumb line control

5. Also check the verticality with the plumb bob. Make sure, at the same time, that the wall is not convex; otherwise, take advantage of it to make it vertical

Thickness control

Thickness control

6. Pull some mortar between the shims to gauge the thickness of future plaster layers. Check that the coating layer (s) do not exceed the defined markings.

Application of the mortar coating

Projection of the plaster body

Projection of the plaster body

7. For make a coating, spoil the trowel to spray on the gobetis. Perform a trowel with a dry hand, as for a tennis backhand. The gobetis facilitates the attachment of this heavy amount of coating; it is made of the same mortar as the gobetis. Its surface is rough. Throw all of your mortar on the wall, if possible at one time. Do not wait until he starts to take!

Drawing of the coating to the ruler

Drawing of the coating to the ruler

8. Before the mortar begins to set, pull the ruler from bottom to top over the entire surface. Take as benchmarks the shims. Advance the ruler in a lateral reciprocating motion. The thickness of the layer will thus be perfectly equalized. Collect the mortar off the ground and project it back onto the wall. Take the surface as many times as necessary.

Removal of the holds

Removal of the holds

9. Remove the alignment blocks by gently blowing them up with the tip of the trowel. The draft of the plaster with the ruler does not give a perfectly flat surface: some gaps can remain. Re-coat them with the same quality as the first used. Spray the trowel in a circular motion. The surface must be flat before finishing.

Smoothing of the plaster and projection of plaster

Reinserting voids left by holds

Reinserting voids left by holds

10. With the wall completely coated, gently close the gaps with mortar, trowel.

Smoothing with a trowel

Smoothing with a trowel

11. Spray the trowel over the entire coated surface. Work as quickly as possible before the plaster begins to set. Start doing this even if the entire wall is not coated. The passage of the trowel allows to further correct the differences in level. It masks the successive stages of progression. It gives a flat and even final surface.

Sponge straightening

Sponge straightening

12. Spray a large wet sponge over the trowelled coating in a rotating motion. This step smoothes the plaster to prepare it for any wall cladding or roughcast.

Using the zip line

Using the zip line

13. Outside, after coat an outside wallyou can project a classic mortar plaster to the zip line, also called "speckled plaster". For make a plaster, this machine consists of a front opening housing to load the mortar. Metal combs rotate inside this housing by means of a crank. They regularly spray plaster particles, which form as many pimples.

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