- Gypsum plaster or DSP
- Used modifiers
- Layout and installation of beacons
- Mix preparation
- Plaster outline
- Stretching and aligning
- Smoothing ceilings
- Removing beacons, grouting
The technique of leveling ceilings is one of the most difficult and time consuming in plastering work. In this review, we will talk about the choice and rules for preparing the mixture, describe the process of its application, leveling and smoothing to obtain the highest quality and durable result..
Gypsum plaster or DSP
Gypsum mixes are good for everyone, except for cost. They are flexible, easy to use, adhere well to almost all surfaces. However, with a large difference in levels, the plaster ceiling can cost a pretty penny. In addition, there are restrictions on the maximum applied layer, on average about 15–20 mm. The maximum layer in practice can be up to 40 mm, but the risk of peeling increases many times.
Cement-sand mixtures do not have such high adhesion, and the mortar life is much higher: up to two hours versus 30–40 minutes. Usually they carry out a rough leveling of surfaces with a large difference in levels or significant curvatures of the plane, and then apply a thin (5-6 mm) layer of gypsum mixture for general strengthening and thorough smoothing.
It is possible to improve the tenacity and performance of the DSP using various modifiers added to mortars for cement and concrete screeds. The concentration for dry powders is regulated by the weight of the added cement (from 2 to 10%), the liquid additives are diluted with water in a ratio of 1: 5 to 1:20 and a mixture for plastering is prepared on this solution..
The main effect of modifiers is to increase adhesion due to polymer adhesive components. It is also possible to entrain air, increase plasticity and slow down the release of water from the mixture. The latter is of key importance for plastering ceilings; it is also a useful property to adjust the rate of cement hydration within 40-60 minutes.
Layout and installation of beacons
Before starting work, the ceiling is thoroughly cleaned of falling off fragments, traces of paint and building mixtures.
The priming with “Concrete-contact” is carried out with the same high care to obtain a uniform shiny film.
Installing beacons is the hardest part of the job. They are placed in increments of 120-150 cm, it all depends on the length of the rule and the skill of working with it. The installation of beacons on the ceiling is more difficult than on the walls, because it is necessary to eliminate sagging by any means and somehow compensate for the inconvenient working conditions. Along the installation line of each lighthouse, holes are drilled with a perforator every 50 cm, plastic plugs are driven into them and self-tapping screws are screwed in.
First you need to mark the ceiling and determine the zero point. The easiest way to do this is with a laser level: we fix it on a bar or wall as close to the ceiling as possible and give it a horizontal plane, then measure the height difference with a flag or a plumbing square for each self-tapping screw and set a mark in millimeters.
You can use a tubular water level by beating off two lines in a common plane on opposite walls. We fasten the lacing along them, it is advisable to pull the ends off with weights. With the help of two paper clips we connect both laces with the third, move it along the entire length of the room and also put marks on the screws.
You already understand that the self-tapping screw at the lowest point of the ceiling must be screwed almost to the very cap, the rest are screwed to the zero level. The lighthouses are simply tightly applied to the caps of the screws, then greased with lumps of pure alabaster. Setting time – about a minute, fixation should be performed in increments of no more than a meter.
When the lighthouse has grabbed, we grease it with a mixture of alabaster and DSP, fix it at least 10-15 cm along its entire length, especially at the edges. Before plastering, you need to wait until it hardens completely, usually about two hours. During this time, we will have time to bring bags with the mixture and prepare it.
Gypsum plasters are mixed according to the instructions: water into a perfectly clean bucket, then powder and mix with a mixer until smooth. After 3-5 minutes, mix the mixture again, after another 5 minutes it will be ready for use.
Before diluting the cement mixture, you must first mix the cement and / or water with modifiers. Ingredients can be added in any order, but if you start with water, no dry lumps will remain in the corners of the container..
Both types of mixtures should be similar in consistency and hardness to butter at room temperature. Too liquid mixture is inconvenient to apply, and too dry poorly adheres to the base.
Unlike walls, the ceiling is not covered with plaster from a bucket, but with a spatula or trowel. No special technique or sleight of hand is needed here, just spread the composition with a thick enough layer, a millimeter “above” the beacons.
One trick is still there: before you cover a certain area with plaster, you first need to wipe it thoroughly. Pour the mixture onto the spatula in small portions and spread with firm pressure so that the metal edge scrapes over the surface.
Regarding the reinforcing mesh: it is usually not used when plastering ceilings, but it can be useful, for example, when leveling a wooden floor over a packed shingle or for strengthening joints between concrete slabs. When gluing beacons, they need to be wrapped with a strip of mesh about 20 cm wide. The edges are then joined to the main canvases with an overlap of 50–100 mm. To lay the mesh, first sketch on the ceiling half of the total layer thickness, then stretch and smooth out the reinforcement with a spatula, achieving high-quality wetting, and then sketch out the rest of the mixture.
Stretching and aligning
The plaster on the ceiling is stretched along the lighthouses with a rule-rail. Choose the length depending on your experience, beginners are recommended to start from 100-120 cm.
Stretching is simple: press the rule tightly with the beveled edge to the edges of the beacons and in one smooth movement pull the mixture, moving the rule longitudinally with an amplitude of 15–20 cm. You need to start from the wall, when you level the area of 40–50 cm – return to the corner and smooth the resulting roller.
When stretching, voids may form where insufficient mixture has been applied. This is a completely normal phenomenon: you need to remove the remnants of the mixture, removed by the rule, on a spatula and distribute them evenly at the beginning of each unfilled section, then stretch the ceiling with a rail again. Small scratches and streaks are not a problem and can be easily removed by smoothing.
If the mixture suddenly runs out, bring the edge of the treated area at an acute angle with a bevel width of about 30 cm.Continue from the same place, mixing a new portion, until the plaster on the ceiling has time to set.
It is necessary to wait about half an hour from the moment the mixture is applied to a separate area. The plaster will harden a little, and you will not break the plane if you try to repair the defects left after stretching. You need to take a steel trowel, moisten it a little and quickly walk along the ceiling, smoothing out large irregularities. Please note that if you did not leave any voids after stretching, the mixture on the ceiling is in sufficient quantity and you do not need to add or remove it..
Particular attention should be paid to the corners between the ceiling and the wall: usually rubble and bumps are formed here, especially if the lighthouses do not adjoin the wall tightly. The corners should be leveled with a narrow (100–120 mm) trowel. It is better to remove a little more of the mixture when leveling, if you are not sure about the general plane. Formed depressions of 1–1.5 mm are easy enough to fill during the finishing grout, it is much more difficult to remove excess plaster.
Removing beacons, grouting
Lighthouses must be removed after the final setting of the mixture, usually this is done after a day or two. The formed furrows are swept out of dust, carefully primed several times and dried. Their embedding must be carried out with a composition that is as homogeneous as possible in relation to the rest of the surface..
While the grout dries, treat the ceiling several times with a deep penetration primer. When the ceiling is dry, it is the turn of the final smoothing. Plaster from DSP is leveled with a polyurethane trowel, applying a small amount of liquid solution and rubbing it thoroughly into the surface, achieving filling of pores and small cavities. The final smoothing of the gypsum mixture is nothing more than the usual puttying with a layer of up to 2 mm. For the highest quality result, here you can go to the finishing plaster mix.
After drying, you need to check the quality of work. Divide the ceiling into two parts, then each – into two more and continue this way until the general plan is divided into rectangular sections with a side of 150 cm.At each of these sections, apply the rule in two perpendicular directions. Recesses larger than 1.5 mm mark with inscriptions indicating the thickness of the layer to be applied. If necessary, level the ceiling again with a finishing putty.