- Wall plastering technology
- Solution preparation
- Preparing the walls
- Installation of beacons and alignment features
- Spray and soil
- Cover layer and grout
Despite the growing popularity of sheet and panel finishing materials, plaster remains a popular way to level walls. In this review, we will describe the technology of plastering work, share the secrets and some features of the process of their implementation..
Wall plastering technology
Plaster is used to form a durable and dense coating on an uneven surface of masonry, suitable for further smoothing and applying finishing materials. At the same time, a requirement is made for the formation of an almost monolithic adhesion with the supporting layer to prevent peeling of the leveling coating under the influence of frost or high humidity..
Leveling the walls with plaster consists in applying a mixture of cement and sand in several stages. First, a solution of a liquid consistency is sprayed to fill the smallest recesses on the surface of the wall and maximize high-quality adhesion to it. After that, a soil is applied – a solution of a thicker consistency, which forms the main thickness of the plaster coating, which is required to level the plane of the walls. At the final stage, the surface is rubbed, eliminating the smallest defects and forming a uniform flat rough finish.
Before the start of plastering work, there are several stages of preparation, however, you need to learn how to prepare the correct plaster solution right away. The fact is that in the process of preparatory work, a certain amount of binding material will be needed. It is allowed to use for these purposes only the same composition that was used when applying the main plaster coating. Otherwise, due to the difference in the degree of linear expansion, cracks and plaster delamination will inevitably appear..
For plastering works, a mortar based on hydraulic binders is used, prepared in accordance with the requirements of GOST 28013–98. As a rule, a cement binder mortar of grades for compressive strength from M10 and M25 for internal and M50 for external work is used. When using Portland cement grade 400, the water-cement ratio of the solution is 1: 1.3, grade 300 – 1: 1.1.
Depending on the specific stage of plastering work, the rate of mobility of the mixture is P3 or P4, for which the ratio of binder to filler varies from 1: 5.5 to 1: 8 (depending on the required grade and the used binder), in general, the less sand, the higher mixture mobility. Also, special attention is paid to the quality of the filler – for spraying and soil, quarry or slag sand, as well as fly ash with a fraction of up to 2.5 mm, can be used, for the covering layer – only sifted quarry sand with a fraction of not more than 1.25 mm.
Preparing the walls
In order to ensure the most durable adhesion of the plaster to the base, it is necessary to properly prepare. First of all, remove all crumbling and loose fragments of brick and masonry mortar, knock down all protruding protruding fragments of the masonry. If there is plaster or other finish on the wall, it is removed completely; by the beginning of work, the bearing layer must be exposed on the entire surface of the wall. After that, the wall must be covered with a hard broom and thoroughly washed with a garden spray or a mini car wash..
The need to prime the walls before plastering is often questioned. Plaster is very demanding on the quality of adhesion of the substrate, therefore any available ways to increase adhesion are extremely useful, especially if the layer of plaster exceeds 30 mm. However, not every primer is suitable for these purposes, for example, film-forming compounds greatly complicate the spraying: the solution simply slides over the primed surface. It is most preferable to use a universal acrylic plaster for highly absorbent substrates, to which stone (quartz, marble) flour is added in an amount of 1/3 of the liquid weight. The walls should be primed under the plaster in one layer. Instead of a primer, you can wipe the walls with special starter plasters, such as Knauf Adgesiv.
Another nuance lies in the use of plaster mesh. Its purpose is not to improve the quality of adhesion to the base, the mesh is needed to ensure the reverse closure of cracks during deformation processes and to exclude flaking of a thick layer of plaster due to expansion during hardening. The mesh must be used with a coarse mesh (over 40 mm); Fastening is carried out in a checkerboard pattern with a step of 25-30 cm, the mesh fabrics should overlap each other with an overlap of one and a half cell widths.
Installation of beacons and alignment features
The main method for flattening and straightening the geometry of the room during plastering is the beacon system. These are thin strips made of galvanized steel of an L-shaped profile with an upper rounded edge, which is used as a guide for cutting off the soil thrown onto the wall by the rule.
Initially, lighthouses are installed on the largest wall with a minimum number of window or door openings, then on the opposite and, ultimately, on perpendicular ones. The wall is preliminarily examined for irregularities by the rule, depressions and humps are marked with chalk. Further, the forces of two people using a long cord are determined by the general irregularities. The task is to find the most protruding point of the wall, which will subsequently be covered with the smallest acceptable layer – 15 mm.
When the cord is stretched with a minimum offset from the most protruding section, it is necessary to measure the indents at the extreme points of the wall, for which the cord is pulled diagonally in cross directions. After that, the extreme beacons are installed 20–25 cm from the vertical corners. Beforehand, the installation line of the beacon is checked along a plumb line to determine the curvature along the vertical axis. Having thrown several lumps of cement mortar on the wall with a step of 30–35 cm, a beacon is applied to them and slightly recessed, making sure that the required indent from the surface is formed at the control point. At the same time, the verticality of the lighthouse is constantly monitored using a plumb line and its straightness using a long rule.
When the extreme beacons are installed, and the solution is firmly seized, two fishing lines are pulled between them 30-50 cm from the floor and ceiling. This lacing serves to align all intermediate beacons in a single alignment plane. To install the lighthouses on the transverse walls while maintaining right angles, you can use an Egyptian triangle or a building bevel with a long ruler. The only difference is that the extreme beacons are installed sequentially, controlling the position of the far beacon by simultaneously monitoring the cord and the protractor.
Spray and soil
At the first stage of applying the plaster, the wall is covered with a thin layer of a sufficient liquid solution, which should drain freely from the trowel. Using a plastering bucket, leave a row of overlapping drips 5-7 mm thick on the wall. In fact, this process is a simple coating of the wall, but using a spatula or trowel for this purpose will not work: the solution is too fluid. After finishing spraying, the edges of the beacons must be cleaned with a spatula.
The spray layer should dry until the solution is pressed a little with your finger, but it stops crumbling. In this state of the surface, you can begin to throw a layer of soil, forming the total thickness of the plaster. Up to a third of the capacity of the mortar is collected in the bucket, which is thrown several times to displace the remaining air and separate a small amount of cement paste on the surface of the lump. The solution itself should have such a consistency that when dropped from a height of 1 meter, the lump will increase in size about 4-5 times without the formation of splashes.
The wall is thrown with a quick and precise horizontal movement and an abrupt stop 15–20 cm from the wall. In this case, the lump should slide along the bottom and wall of the bucket, and then be thrown outward along an almost horizontal path, but with a slight toss up. Getting your hand to work with a bucket is not difficult, you just need to practice for a while. It is very important that the lump of mortar hits the wall with little but sufficient force for a good seal. Flip flops should be laid tightly enough so that the bumps protrude 3-5 cm beyond the plane of the lighthouses, and the deepest areas of the soil are either in the leveling plane or 3-5 mm deeper.
The soil is thrown in separate sections between the beacons in the direction from the bottom up. If the thickness of the soil exceeds 35–40 mm, it is better to perform the cast in two stages, otherwise there is a high risk that the massive pile of mortar will come off the wall and collapse. When the whole area between the lighthouses is covered with soil, it must be left to set for 15–20 minutes; in the process of waiting, you can throw in adjacent areas. When the solution has grabbed a little, the sharp edge of the rule is pressed to the beacons and the protruding mounds of the solution are cut in the direction from the bottom up, simultaneously making “sawing” movements with the rail. The cut solution is suitable for further use if you mix it with fresh in equal proportions, which is why it is recommended to apply the soil sequentially to the areas between the beacons, and not to the entire wall.
Cover layer and grout
After applying the primer, a fairly large number of grooves remain on the wall, while small plateaus are formed that lie in a common plane. In addition, to eliminate the appearance of rusty spots, the beacons must be removed, after which furrows will remain. To eliminate all these grooves and finally smooth the surface, the wall must be wiped. For these purposes, a solution is used, the consistency of which is approximately halfway between the mixture for spraying and soil..
For finishing leveling, it is most convenient to use a polyurethane float. Grouting should be carried out when the soil layer has set for at least 20 hours. It is possible later, but the wall must first be well moistened. A small lump of mortar is placed on the corner of the grater, which is pressed into the recess with force and rubbed with movements in different directions. When all the irregularities are filled, you need to spread a thin layer of mortar on the working surface of the grater, lean it against the wall and, with a little pressure, make a sweeping movement in perpendicular directions. After the common plane is displayed, the movements with a float are changed to circular. At the same time, you can spray the wall with water so that only the finest grains of sand accumulate on the surface, leaving no deep scratches.