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Facade plaster around the openings

The realization of a cement mortar facade coating is applied to the hand or the machine, in one, two or three layers. The presence of openings, doors or windows, is a difficulty that leads to the establishment of a formwork specific to this level. This operation is not particularly difficult. She just asks a lot of care.

Installation of the formwork

The lateral formwork elements are held in place by one or more spacers engaged in force to ensure their spacing and maintenance.

Installation of a window formwork

Forms must be made to ensure the stopping of the coating at the openings of the wall: windows and doors. Plywood or plank strips 19 to 22 mm thick are generally used. These formwork elements must extend approximately 25 mm from the surface of the wall, which corresponds to the thickness of the plaster layers:

  • gobetis 5 mm
  • plaster body 15 mm
  • finish 3 to 5 mm

The adjustment of verticality and thickness of the formwork strips is done by small hammers given on the edge of the boards.

Adjusting the vertical slats

A plumb line or a bubble level makes it possible to control the verticality of the vertical formwork elements. Thickness adjustment and verticality corrections are made by hammering the edge of the formwork.

The mortar is spoiled in trough or on area. The tie layer (gobetis) is made of a mortar rich in cement. The finishing layer uses a fine sand (the binder must never be pure cement, but a mixture of cement and lime).

Application of the mortar coating

The gobetis mortar and plaster body is trowelled to form homogeneous layers.

Thrown mortar

Gobetis and plaster body
The mortar is troweled between the slats in two layers: the gobetis or primer layer and the plaster body. The technique for throwing the mortar is quite easy to acquire. You have to take some mortar on the end of the trowel and throw it on the support with a wrist movement.

The dressing of the coating is done in the rule (a wooden or aluminum slat). The thickness of the finishing layer must be taken into account.

Equalization to the rule

Dressing the plaster
The dressing of the plaster is done with a long rule of mason who slips on the slats. The ruler flattens the surface and removes excess mortar, then smooth with a trowel. When the mortar has set, remove the slats and reseal immediately with the mortar.

It is necessary to wait 24 hours between the gobetis (layer of attachment) and the body of plaster, and several days between this one and the finishing layer. It is necessary to smooth perfectly the topcoat which must not show any irregularity.

The finishing layer is smoothed. It must be moistened regularly so that it slides well on the mortar.

Smoothing the topcoat

Smoothing of the plaster
The finishing layer (which some dispense) consists of very fine mortar which will be smoothed with the trowel. This layer must be very precisely flush with the edge of the shuttering boards of the openings.

Drying the facade plaster

The weather often causes problems for drying coatings. Refrain from making a coating when it rains, when the weather is cold (risk of frost) or by heat (drying too fast):

  • if there are Chance of Rainprotect the coated surface with tarpaulin or plastic film;
  • it frozen, postpone the project;
  • if he does hot, slow down the setting and therefore the drying by water sprays (in small quantity).
Note that the complete drying time of the mortar is of the order of 28 days.

(photos / visuals: © DIY-Prod, except special mention)

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