How to plaster

Should I choose gypsum or cement-lime plaster? How about so-called drywall with plasterboard? We have to answer this question after analysing the use of the rooms we intend to plaster. Whether it is living quarters or basement, office or warehouse, attic or ground floor. Each of the available solutions has its advantages.

Cement-lime plasters have their advantages when used in rooms with high exposure to mechanical damage. This type of plaster is more costly in the execution process, but has better applications in public buildings, schools, kindergartens, warehouses or basements and garages. The advantage of cement-lime plaster is its very high water resistance, the possibility of using it in wet rooms, i.e. baths, swimming pools, drying rooms, high frost resistance and the vapour permeability of the plaster. The disadvantage, however, is the cost incurred in making this type of plaster. With cement-lime plaster, additional filling of the entire surface is required in order to achieve the desired smoothness. This involves double the cost of workmanship and higher material costs.

Gypsum plaster , on the other hand, is far more applicable to multi-family and single-family housing. Excellent smoothness and high surface quality at a low cost are huge advantages. The surface does not need to be additionally smoothed and can be finished using any technology. The use of gypsum plaster inside the building also has an effect on saving heat consumption. Gypsum plaster has beneficial thermal insulation, sound insulation and fire resistance parameters. It also has the advantage of maintaining a human-friendly microclimate – the gypsum absorbs excess moisture and gives it back when the room is too dry.
The disadvantage of gypsum plaster is its aggressiveness which causes corrosion in steel components. If gypsum is used, such components must be protected against corrosion by protective painting, varnishing or galvanising. Gypsum plaster is not suitable for areas with sustained high levels of humidity, such as swimming pools or bathrooms. Gypsum plaster is also not suitable for use outside the building.

Which plaster to use in our home? A simple principle may be adopted:
Cement-lime interior plaster is used when the house is made using traditional technology – brickwork with materials ensuring high vapour permeability, e.g. hollow bricks, porotherm ceramic blocks, and external insulation made of mineral wool. As a final touch, we use a mineral coloured plaster finish or silicate or silicone paints. This is a more expensive method, but more effective.
Gypsum plaster, on the other hand, is chosen for masonry made of calcareous materials such as Suporex or silicate. We insulate the external walls with polystyrene and apply acrylic plaster and gypsum plaster inside.

Which corners to use for cement-lime plaster?

When making cement-lime plaster, we use steel corners coated with protective coatings – usually hot-dip galvanised or, more recently, hot-dip galvanised with the factory name Magnelis. This type of plaster dries quickly and rarely rusts the corner. In steel corners, corner cuts and ridges are a critical point where the galvanised coating can be damaged during grinding. Damaged areas are more likely to develop rust outbreaks.

The idea to improve the protection of steel is a new coating used instead of standard galvanisation – Magnelis coating. This is an innovative type of corrosion protection used in plaster corners. The chemical composition of the Magnelis coating has been optimised to achieve the best anti-corrosion properties. Magnelis coating contains an admixture of 3.5% aluminium and 3% magnesium. It is this 3% magnesium content that is decisive, as it is what creates a stable and strong coating over the entire surface of the sheet, guaranteeing much more effective protection against corrosion than coatings with a lower magnesium content. Please note – when cement-lime plastering – aluminium corners must not be used.

Which corners to use for gypsum plaster?

Gypsum-based plaster mixtures, in the presence of water, exhibit a strong, aggressive, chemical action. If these plasters are used and the walls are expected to take longer to dry, aluminium or stainless steel corners should be used.
Experience shows that nowadays walls are quickly erected, the building is closed with windows and a polystyrene façade is almost immediately applied.  In such a tightly sealed building, wet internal plaster, usually gypsum, is often laid without adequate ventilation of the rooms. The walls retain a high level of moisture for a long time.
We recommend using aluminium or stainless steel corners in this situation .
Such corners show much greater reliability with sustained high moisture levels in the wall. Steel corners should not be used for gypsum plaster.

How do you plaster a wall?

The method of plastering walls varies depending on whether cement-lime plaster or gypsum plaster is used and the method of application – by machine or by hand.
Due to the wide variety of plaster mixtures on the market, the manufacturer’s recommendations should be read carefully each time a mixture is changed.

Step 1:
Regardless of whether the substrate is new or we are plastering renovated buildings, the plastered surface must be prepared as standard. It must not be dusty, with remnants of old paint, holes or greasy. We properly clean the substrate, fill in the defects and prime. The corners of the walls are secured with suitable strips – plaster corners. The use of plaster corners is important because vertical and horizontal corners are easier to lead out when plastering, and they are also intended to protect the corners from mechanical damage during the use of the building.

Step 2:
Walls with a very large surface area should be divided into smaller areas using special metal guide strips, which are selected according to the thickness of the plaster we are using. These strips will help us to achieve an even surface of the plastered wall. With small wall areas, the use of such a moulding is unnecessary. Fix the guide strips to the wall at a distance of approx. 1 m one from the other. These strips are protected by galvanisation and remain in the wall after plastering. When plastering, care must be taken not to damage them, as this can cause them to rust.

Step 3:
On a prepared substrate, with a temperature of at least + 5 deg C, we can start plastering.
Once the plastering is complete, we must ensure that the environment is at the right temperature and ventilated. The plasters should not be dried too intensively, nor should they be brought into sharp draughts. It is advisable to ensure that the rooms are sufficiently ventilated to gradually remove excess moisture from the drying plaster.

How do you plaster a ceiling?

Step 1:
We start plastering the rooms first by applying mortar to the ceiling, and only after the ceiling is finished do we plaster the walls. The prepared mortar (according to the manufacturer’s instructions) is applied to the ceiling by hand or, more commonly these days, by machine.

Step 2:
Once the mortar has been applied to a section of the ceiling, begin the initial levelling of the mortar with an ‘h’ patch, holding it with both hands in front of you and pulling it towards you. The levelling of the ceiling surface should be carried out in different directions so that an even plane is achieved. Any excess mortar left on the patch when levelling the surface is collected and any unevenness in the ceiling where mortar is missing is filled in. After levelling the mortar, carry out a preliminary level check of the ceiling with a long spirit level by applying it at various points. Any deviations from the horizontal must be corrected before the ceiling dries.

Step 3:
When the mortar begins to dry, it is necessary to smooth the surface of the plaster. This is done in order to obtain an even and smooth surface. Just before the plaster mortar has completely hardened, the plaster surface on the ceiling is sprayed with a diffused jet of clean water (so-called mist). The moistened mortar surface is trowelled with a sponge trowel and then with a long spatula. When trowelling, use circular hand movements to achieve a perfectly smooth surface.

For the preservation of a beautiful façade over a long period of time, proper and successive maintenance is very important. Any repairs to damage in the façade should be carried out on an ongoing basis to prevent the cavities becoming larger and degrading further. What can be done to ensure that the plaster retains its initial appearance?

Remove dirt on an ongoing basis. The method should be chosen according to the degree of contamination. If it is small, it is sufficient to use cold water at low pressure (up to 5 atmospheres). For larger and more extensive dirt, it is best to hire a specialist company to expertly clean the façade without risking damage to the plaster. Drainage systems such as gutters and drain pipes should be systematically inspected. The failure of these components to function properly can cause water stains which will create a good breeding ground for fungi and algae, which in turn can lead to chipping and flaking of the plaster.

The maintenance of plasters also includes painting  them (one coat of paint in the colour of the plaster is particularly recommended for mineral and silicate plasters, as it allows better colour retention). However, it is always important to remember to choose the right paint for the type of plaster. Silicone paints can be used on all types of plaster, acrylic paints only on acrylic and mineral plasters and silicate paints on silicate and mineral plasters.

In addition to its aesthetic importance, painting of plaster is also important to improve the hydrophobic and adhesive properties of the plaster, i.e. improve the resistance to water absorption and reduce the tendency of the plaster to become dirty.

Internal plasterwork can be carried out in winter, with external temperatures below freezing, subject to conditions.

A temperature of at least 5°C must be maintained in the plastered rooms – this also applies to the temperature of the plastered surfaces. A major problem that occurs when plastering interior walls in winter is the drying out of the plaster, which is dependent on the conditions on the construction site. It is related to space heating and ventilation. Heating rooms without ventilation does not lead to drying out of the walls. Wall drying is particularly important when using steel strips covered with various types of anti-corrosion coatings. It is important to remember that all coatings are only a temporary protection and that staying too long in damp plasterwork will end up with corrosion symptoms.

Plastering work carried out in winter involves additional costs for heating and ventilating the premises during plastering and throughout the drying of the plaster .

Various types of dehumidifiers can be used to achieve a rapid reduction in the humidity of rooms and thus walls, but these methods are expensive and only work locally.