There are a few reasons why walls need to be plastered. It is most common during renovation and new construction or when lines and pipes have been relaid. Defects have to be repaired and the walls have to be re-plastered. With a little practice, you can also do this as a hobby craftsman, but there are a few things to consider. The selection of the plaster is of crucial importance, because plaster is not the same plaster and the preparation of the substrate. Plaster in the true sense is a covering made of mortar and different binding agents. It creates smooth surfaces, but at the same time protects the inner walls and improves moisture regulation in the interior.
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Types of Plaster
What types of plaster are distinguished?
Plasters are not uniform. They are made of different materials. There are also different cleaning techniques. When plastering, it also depends on the purpose for which it is needed. Basically, a distinction is first made between the binders used:
- Differentiation according to binders – the means contained decide on the properties and the intended use
- Mineral, inorganic binders (cement, lime, clay, silicate)
- Organic binders (gypsum, synthetic resin)
- Differentiation according to aggregates – influence the technical and building physics properties, i.e. coloring, thermal conductivity, structure formation and reinforcement
- Mineral aggregates (gravel, rock flour, quartz sand, crushed bricks)
- Organic additives (glass flour, fiberglass, straw, animal hair)
- Lightweight aggregates (cork, expanded clay, foam glass granules, vermiculite)
- Compensation and additives
- Differentiation according to plaster thickness, plaster technique, plaster function, plaster components and wall design
The base plaster is used most frequently. It serves as a base for paint, wallpaper or decorative plaster. It can be applied as a hand plaster, spatula plaster or with a machine.
Hand plaster – most commonly used by hobby craftsmen, the ready-mixed plaster is thrown onto the wall with a trowel and this mass is then leveled with a leveling board or grapeshot. It is important to distribute them in a plumb and flush manner. Depending on what the top covering should look like, it then has to be smoothed, felted or simply straightened. The layer thickness of this plaster must be 8 to 10 mm at the end.
Thin and spatula plaster – can be applied manually or by machine, but you need an absolutely even surface. The layer thickness is 2 to 5 mm.
Machine plaster – Mortar is mixed with a lot of water in the plastering machine and sprayed onto the walls and ceilings using compressed air through a hose. This must then be manually distributed flat with a leveling board or grapeshot. This layer is at least 10 mm thick.
No matter which plaster and which type of plaster you choose, it is important to work quickly. The damp plaster must be applied and smoothed quickly and evenly, otherwise an uneven surface will result and the beginnings and transitions will be visible. These areas have to be sanded down again at the end. Plastering a wall is not very difficult, but if you are meticulous and want a really smooth surface, you usually have to practice a little before you can do it. If you can, you should start with a wall in the basement, in the utility room, in the hobby room or in the garage until you really get the hang of it.
Cleaning alone is very tiring. You have to imagine it like this:
- A sack of gypsum plaster (30 kg) with a plaster thickness of 10 mm is only sufficient for an area of 2.5 m², which is not much.
- 1 liter of material is required for a plaster thickness of 1 mm on 1 m²
- For 10 m² and 10 mm thickness, that’s 160 kg to distribute.
- Masonry trowel – for throwing the plaster on the wall, preferably made of stainless steel to avoid rust spots in the gypsum plaster
- Smoothing trowel – to apply plaster
- Grout (trowel) – used to smooth and rub freshly applied plaster for greater strength and a more even finish
- Smaller trowels (cat tongues) for tight spaces (around windows and on door frames)
- Sponge board – for felting the plaster surface while setting
- Plaster Gauge – helps to apply the compound evenly, consists of strips and corner rails
- Cleaning machine (can be borrowed from the hardware store) – difficult for laypeople, as it has to be done extremely quickly
Plaster doesn’t stick to every wall. The prerequisite is that the substrate is dry, firm and stable. That’s why he needs to be examined. With a new building, everything is usually fine, but you have to be very careful with old buildings or when renovating houses that are not that old.
If cracks, crumbling parts or mold can be seen, the wall needs pre-treatment. Loose parts and dirt must of course be removed. To test whether the wall is holding up, you can press on a piece of adhesive tape that sticks strongly and then pull it off with a jerk. Nothing should stick to the tape itself. Depending on the damage or dirt, the wall can be cleaned with a hard broom or a sandblaster . An important test is: slightly moisten the wall surface with water and observe the drops.
- If these remain, the substrate is not absorbent
- If the water is slowly absorbed, it is normally absorbent and ideal for plastering
- If it absorbs quickly, the surface is highly absorbent
- This test is decisive for the further procedure
- The suction behavior determines which primer has to be used
- Normally absorbent substrates only require a deep primer
- Highly absorbent substrates, on the other hand, require an adhesive emulsion
All rough unevenness must be removed before plastering work begins. The floor and all surfaces that are not to be plastered should be covered or masked over a large area.
If there are corners whose adjacent walls are to be plastered, sheet metal corner profiles are used (outside corners, not those at a 90° angle). Place the profiles directly on the corner and apply plaster profile mortar in small quantities to the edges. The sheet metal is pressed with a straightedge. Smooth out excess and oozing mortar. The plaster must dry for at least 1 hour before work can continue. Attach plaster profiles, also plaster slats or plaster strips. They serve as a guide as to how thick plaster must be applied. Like the corner profiles, they remain on the wall and finally disappear completely under the plaster layer. The profiles must be exactly vertical. Choose a distance between 1 and 1.5 m.
Properly plaster interior walls
After a good preparation, the actual plastering can now begin. First the plaster is mixed, then the wall is made slightly damp and then the first layer of plaster follows.
Mixing plaster is uncomplicated. You need a large container, clean water and the actual plaster mortar, usually in large bags or sacks. You just have to follow the manufacturer’s instructions and mix the mass according to their instructions. It is important that it is mixed well, which works best for small amounts with a large mixing spoon. For larger quantities, an electric stirrer is recommended . Drills with a mixer attachment usually do not develop enough power. A wheelbarrow is often used for mixing, which is also not recommended, because the different heights make it difficult to stir well and evenly.
If the plaster base is well prepared, which means that any required primer has also been applied, the wall should be wetted, as the professional says. Water is simply sprayed on the wall, preferably with a paste brush, ceiling brush or alternatively with a painter’s brush. One should not be stingy with water, because the wall to be plastered should be damp.
A masonry trowel or spatula is ideal for applying the mass . Both tools can be used to throw the mortar mass against the wall. Throwing has the advantage that the mass gets into fine cracks and grooves due to the pressure, which is not the case with normal application. Alternatively, a smoothing trowel can be used to apply the mortar. Practice is required here, starting is not easy.
- Plaster strips and corner profiles are ideal for large plaster surfaces. They protect the edges from damage and wear.
- Quick plaster strips are very helpful when leveling sloping walls. They are mounted the day before at a distance of approx. 1 m perpendicularly and flush with the walls. When applying and removing the plaster, the strips then prevent the removal of the excess plaster from aligning itself with the uneven walls.
- It is important to work quickly.
- Spread a complete layer over the entire wall
Second layer of plaster
If the required layer thickness has not yet been reached, the plaster strips are still visible or individual areas have not yet been evened out, a second layer is necessary. The mortar mass is no longer thrown against the wall, but applied with a smoothing trowel and drawn onto the wall. It is important to remove the excess plaster, i.e. to pull it off. It is best to use a straightedge or gauge for this.
At the very end, the wall still has to be filled. To do this, however, it must be dry, which is only the case after a few days. The length of the drying time depends on the type of plaster and application thickness. As long as the plastered surface is still dark, that means the plaster is still very damp. The lighter it gets, the drier the area. Only when it has dried properly can it be sanded down and then filled.
The filler must be mixed according to the manufacturer’s instructions. Then it can be roughly applied with a spatula and then distributed criss-cross. Always work from bottom to top and very evenly. If everything has been smoothed off, pull off the wall again from bottom to top and smooth it out completely. If there are still uneven spots after drying, repeat the process until the wall is smooth.
Now the wall can be painted, wallpapered or designed with decorative plaster.
Extra: plaster the outside walls
In principle, there are no major differences between plastering interior and exterior walls. However, the plasters are different. Machine plaster is usually used outdoors. This not only has optical tasks, it also protects the house facade. Hobby craftsmen can also plaster their house from the outside, but those who are very inexperienced but experienced should get help. Here, too, it depends on the subsoil. It must be clean and even. A primer with adhesive emulsion is recommended for bricks or aerated concrete.
- The wetting of the wall is also important here. The mineral plaster is applied to the wall in sections and distributed.
- Plaster must not dry out
- No temperatures below 5°C and above 30°C
- During the entire time and the drying time, protect the plastered wall from strong sunlight or driving rain.
You can plaster walls yourself, even as a hobby do-it-yourselfer, but it takes time and requires strength. Working on a wall or a room is certainly not the problem, but a whole newly built house is, because experience has shown that it takes forever. Professionals usually need only half the time or even less and their results are often more satisfactory. But if you really need to save, you can do it yourself, but you should take your time. It is advisable to practice on walls that hardly anyone ever gets to see.