- The difference in the composition of the gypsum putty
- Preparing walls for plastering
- Preparation for work
- The sequence of leveling plasterboard and plastered walls
Gypsum plaster provides excellent opportunities for very high quality leveling of surfaces. Correct filling ensures not only perfect wall plane and room geometry, but also a very smooth coating with good adhesion. We will tell you about the choice of compositions and the technique of working with them in this material..
The difference in the composition of the gypsum putty
Today there are two main varieties of gypsum leveling mixes with clearly separated areas of application. These are starting and finishing mixtures, which for brevity are called gypsum plaster and putty, respectively..
The starting compositions cannot be confused with anything: they have a granular crumbly structure with interspersed sand and a color from beige to dark gray. The final mixture has a homogeneous consistency – it is a snow-white powder, almost powder. Start and finish also differ in density – putty is about 20% heavier than plaster.
The scope of application for both types is different. Due to the heterogeneous structure, starting plaster can be held in a sufficiently thick layer – up to 30 mm, and even more with the use of a reinforcing mesh. The starter works well with sub-average adhesion surfaces: cement plaster, masonry or block masonry. Start is applied either manually with spatulas or by a gunning machine.
Shotcrete with a finishing putty is difficult: due to the high viscosity of the composition, it is difficult to break it into small splashes. In addition, it is common practice to use the finish line as little as possible. This is justified from the point of view of economy (the finishing putty is more expensive than the starting one), besides, the smaller the finish leveling layer, the better the coating behaves during operation..
As a preliminary result, we will understand one rule: the start is used to level out irregularities and general blockage of walls and ceilings, sealing joints and processing corners. The finish, in turn, creates a smooth, hard crust with good adhesion, which is ideal for most decorative materials.
Preparing walls for plastering
Plastering walls with gypsum mixes of any type requires extraordinary patience and care. Very often, due to the incorrect definition of the work front and poorly prepared rough surfaces, situations occur when the plaster is poorly absorbed, or during work, large pebbles and lumps are found in the mixture. It is much more deplorable when the result of negligence in preparing the walls becomes visible after a few years in the form of rusty spots or peeling of the leveling layer.
Preparation, depending on the type of rough surfaces, may include the following steps:
- removal of lighthouses from plaster;
- removal of any metal elements on the surface or 15–20 mm below it;
- dedusting the surface up to thorough washing with water;
- priming with deep penetrating compounds, especially for lime plaster with a low cement content;
- priming of some types of surfaces (chipboard, OSB, magnesite plates);
- abrasive cleaning of surfaces with a glossy layer;
- complete natural drying of the wall.
Gypsum plaster, despite its versatility, should not be applied to clean walls made of shell rock and other structures with high porosity. First, apply a thin layer of cement-sand plaster, which limits absorption and reduces consumption. This perfectly demonstrates the general trend: the lowest quality and cheapest materials are used for a gradual rough leveling, and closer to the front plane they use higher quality materials, but in much smaller quantities..
Preparation for work
To manually putty the walls, you need a mixer with a 45–60 mm whisk, two clean plastic containers (preferably 15–20 liter buckets), a set of spatulas and trowels. From the last group, spatulas of 40, 100 and 350 mm are required, a rectangular 200 mm trowel, an angular spatula is also preferable.
Puttying should be done promptly, because the life time of the mixed putty is from 25 to 40 minutes and it is no longer possible to add water to it after the start of setting. Therefore, the space at the wall to be treated must be free for the smooth movement of the ladder or scaffold along with everything necessary. In other words – provide for a maximum of extraordinary situations, keep a clean rag and a bucket of water at hand.
When the workspace is completely ready, proceed to kneading the putty. It should be carried out only in a clean container and only with a clean instrument: even minor inclusions of the old mixture can shorten the life time of the fresh composition by 15–20 minutes. First, the required amount of water is poured into the container – approximately 2/3 of the required volume of putty.
The first portion of the dry mix is added in a volume approximately equal to the volume of the amount of water. Pre-mixing is performed, then dry putty is gradually added to the liquid mass until the consistency of liquid sour cream is obtained. The mixed filler must have such a thickness and viscosity that a full 100 mm finishing trowel, laid on the edge of the trowel, does not slip under its own weight. The consistency of the starting putty can vary widely due to the fact that its linear drying shrinkage is not so pronounced.
The sequence of leveling plasterboard and plastered walls
Before puttingtying the surfaces, the outer corners and joints between the sheets are strengthened. The requirements for embedding at this stage are very strict and the appearance of the finished surface depends on the technically correct approach to work, which is especially important for decorative coatings without their own fastening base.
The surface requirements for wallpapering are the least stringent. The starting mixture used for embedding and strengthening is quite flexible and convenient for eliminating local and general irregularities, including those that remain from embedding. Residual roughness is removed with a thin covering layer of the finish, after which the wall or ceiling is ready for wallpapering. As a rule, there is no need to cover the entire plane with a putty, if you can limit yourself only to seams and traces of fastening, and then carefully prime the surface. But if the wallpaper literally shines through, a thin continuous layer of the finish is still necessary..
Baseless coatings (textured and Venetian plaster, paint) do not hide the appearance of even the smallest cracks. Therefore, the plastering of plastered walls should be carried out in two stages. At the first stage, the wall is covered with a thin layer of start, a fiberglass or mesh is applied to it with an overlap of 30–50 cm, which are smoothed tightly with a wide spatula from the center to the edges. At the second stage, the wall is covered with one or more finishing layers until a surface with the required roughness value is obtained..
As for the technique of working with gypsum mixtures, then everything here is determined by practical experience. The main essence of working with a spatula is the angle of its inclination relative to the surface: a flatter position entails the imposition of an additional layer. The closer to the right angle, the less putty is applied to the surface, and with additional effort it will be removed altogether.
Begin leveling with small areas using a 300–350 mm wide trowel. The mixture is applied according to predetermined grooves and leveled in different directions. With each subsequent layer, the width of the trowel and the area of the treated areas should increase. Lack of experience in puttying can be compensated for by cleaning with abrasive meshes or sponge washing, although such post-processing should be avoided due to the high labor intensity of the process.