What is interior plaster

Overview of types of plaster

Plastering in the interior: an overview of different types of plaster for walls and ceilings

When it comes to the initial coating, renovation, renovation or design of walls, plaster is an important building material. Find out in advance about the properties, processing and advantages and disadvantages of different types of plaster in order to avoid mistakes on your construction site and to save time and money when buying materials. In this overview of the different types of plaster for interior walls you will find helpful information to make your choice easier.

Classic and modern types of plaster for interior walls

There is hardly a living area that attracts more interest and attention than the interior walls. In order to professionally coat and beautify them, there are numerous types of plaster for base plasters, finishing plasters and decorative plasters. Today, plaster can basically be any smooth, fine or coarse-grained mix of materials that is offered as a powder or paste and that you can apply to the wall in one or more layers when damp, structure it and allow it to harden.

Plaster or plaster mortar are bound substances. In addition to the main ingredients (usually sand and water), they contain mineral or non-mineral binders such as lime, gypsum, cement or clay. Many types of plaster are enriched with additional substances that improve their properties, such as air-entraining agents, adhesion improvers and setting accelerators. Color pigments, structural and fillers as well as active ingredients (e.g. against mold or algae) can also be contained in the plaster.

For a construction site mortar in the classic sense, the ingredients are obtained separately and then measured (dosed) and mixed together on the construction site. For plastering in the interior, however, are usually already ready mixes (so-called factory mortar, dry mortar or factory dry mortar) to which only water has to be added according to the manufacturer's instructions.

Until a few years ago, only mineral mortar coverings or mineral-bound plasters were considered to be plaster DIN 18550 (Plaster mortar groups). In the meantime, however, this term has been expanded to include synthetic resin plasters and special plaster systems for thermal insulation. The standards for synthetic resin-bound plasters are in DIN 18558 set.

Note: The name of the plaster is always given by the binding agent.

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Tasks of plasters and plaster systems

In earlier centuries plasters were mainly used for Flattening and embellishment thick walls. Today, the wall cross-sections are much smaller, and many walls are made of porous building materials that attract water. As a result, plasters and paint coatings can now perform far more tasks, and as a result, the demands on the materials have also increased.

Plasters protect against the effects of the weather, dirt, mechanical and chemical loads. They form the coating base for stable and decorative coatings and improve moisture resistance, sound and heat insulation and flame and fire protection. Multi-layer plasters with different types of plaster are called plaster systems.

So that types of plaster and plaster systems can also develop their favorable properties, they must be processed and built up correctly. The layer thickness and compressive strength of the sub-plaster must be higher than that of the finishing plaster, otherwise flaking and cracking can occur. Before applying the top coat, the base coat must have hardened but not yet completely dry. And because plaster adheres better to rough surfaces, it is advisable to only level the plaster, but not to smooth it.

Note: The minimum compressive strength of a plaster is also specified in DIN 18550, 15885 and other plaster standards. For do-it-yourselfers, builders, renovators or planners without the appropriate professional training, however, it is usually easier to seek advice from a professional in a specialist shop or directly on the construction site.

The most common types of interior plaster are gypsum plaster, gypsum-lime plaster, lime plaster, lime-cement plaster and clay plaster. There is also increasing demand for plaster systems for thermal insulation or for moisture and mold protection. All corresponding types of plaster are available as ready-mixed dry mortars in sacks, silos or smaller containers (e.g. buckets).

Overview of types of plaster

Gypsum plaster

Gypsum plaster is the most frequently used interior plaster for residential buildings and is considered a high-quality standard for all common interior work. The mineral material is very fine-grained and smooth, is easy to work with and is an excellent substrate on walls and ceilings for top and decorative plasters, wallpapers and paint .

By nature, plaster of paris is flame retardant. From a building biology and building physics point of view, gypsum plasters ensure a low-irritation, warm and dry room climate. Their ability to bind water and release it again when the room is more dry also increases the fire protection effect.

Advantages of gypsum plaster:

  • Building biologically and ecologically harmless
  • moisture-regulating, but not water-repellent (no condensation or "condensation"
  • vapor diffusion open (breathable)
  • Suitable for all walls or rooms that are normally exposed to moisture and stress
  • very inexpensive

Gypsum plasters such as the popular adhesive plastering plaster are applied with hand tools and stick to almost any rough surface, such as masonry, concrete, plasterboard, cement or other plasters with sufficient compressive strength. If you attach a suitable plaster base beforehand, e.g. B. expanded metal, you can also use it to plaster wood.

For damp rooms such as bathrooms, kitchens, garages or basements, there are gypsum plasters with increased strength that contain a special primer. These damp-proof plasters save the additional primer layer before tiling and are also often used in bathrooms and kitchens in which a large part of the wall surface should not be tiled, but designed or decorated differently.

Note: Plaster of paris sets very quickly and hardens after around an hour. Setting cannot be prevented by adding more water. You should therefore take into account the manufacturer's information on processing and drying times and mix gypsum plaster more often and then in smaller quantities.

Lime plaster

Mineral lime plasters regulate air humidity and room climate and, due to their alkalinity, also prevent the formation of algae and mold. The spatial effect that a lime plaster creates depends primarily on its grain size: the finer the material, the smoother and more elegant the surface appears.

Lime plaster can be modeled, felted or washed out in the wall design. Natural lime plasters or organic lime plasters are mostly intended for low to normal use, but many modern lime plasters (e.g. the reddish brick flour plaster) have a higher abrasion resistance due to their formulation. Smooth lime or special lime-silicate coatings are suitable for further treatment or coating in living spaces.

Advantages of lime plaster:

  • Building biologically and ecologically harmless
  • breathable (open to diffusion)
  • improves the indoor climate
  • moisture regulating, but not water repellent
  • disinfectant and anti-mold

However, the positive properties of lime plaster only come into play when the entire plastering and coating system is correctly set up. So ask a specialist whether you B. May use deep primer, whether the existing substrate matches the lime plaster and which materials are suitable for professional further treatment (e.g. for painting) the plaster surface. This is the only way you can be sure that the work is worthwhile and that you will actually benefit from all the advantages of this material later.

Note: Lime plaster is highly valued in ecological construction because of its favorable biological and structural properties. However, it is quite expensive and not as easy to work with the layperson as gypsum or cement plaster.

Lime-cement plaster

Lime-cement plasters are also traditional or classic mineral plasters. In the interior, they are mainly used for wet and damp rooms as well as walls with medium to high loads. Lime-cement plaster is robust, durable and, due to its strength, also suitable as a thick base plaster (which is applied directly to the wall).

Advantages of lime-cement plaster:

  • Building biologically and ecologically harmless
  • moisture-resistant and water-repellent (also good weather protection outdoors)
  • high mechanical resilience (abrasion and pressure resistance)
  • open to diffusion, high resistance to moisture and weather
  • high degree of hardening
Note: Because of the cement content, this type of plaster is comparatively brittle and therefore more prone to stress cracks. In addition, lime-cement plaster is only conditionally suitable for heat-insulating plaster systems (e.g. the processing of heat-insulating wall blocks).

Clay plaster

Roughly or smoothly processed clay interior plaster can be used in many living areas. The cleaning material consists of cleaned, ground earth or a fine earth-sand mixture, such as clay powder and marble sand. Straw and other plant fibers, plant starch, cellulose, color pigments or special effects (e.g. mother-of-pearl) can be added for a better bond and for refinement.

Clay plaster is quite expensive and can be used as a finishing plaster or decorative clay plaster on almost all substrates. It is softer than gypsum and lime plaster and therefore not suitable as a substrate for these types of plaster.

Clay plasters are popular for renovating and beautifying old buildings as well as for ecological construction. They are particularly valued for their natural aesthetics, creative design options and positive effects on the living environment.

Advantages of clay plaster:

  • very good climate and moisture regulation
  • heat insulating
  • non-flammable
  • open to diffusion
  • sound absorbing
  • minimizes fine dust, pollutants and allergens in the room air
  • many individual processing and design options
  • suitable for old or historical building and coating techniques
Note: When planning, make sure that clay plaster is water-soluble. You should therefore round off the edges or seek advice from a specialist on suitable edge protection techniques.

Clay gypsum plaster

Clay-gypsum plaster combines the advantages of two types of plaster: It is better suited to regulating room humidity and the living climate than gypsum plaster and, compared to clay plaster, offers greater strength and faster drying times. In this way, it can be processed better or in thick layers as a single layer and later provided with common diffusion-open paint coatings.

Thermal insulation plaster

Thermal insulation plasters are plaster mortars with a particularly low thermal conductivity. In order to achieve the appropriate values, special additives are added, such as perlite, vermiculite or polystyrene (EPS). At the same time, thermal insulation plasters according to DIN 4102 should be flame-retardant (building material class B 1) or non-combustible (building material class A 1).

Because of the additives it contains, thermal insulation plaster has a low inherent density and is therefore also referred to as lightweight plaster. It is often used as a flush on stone walls and masonry, which otherwise do not achieve the desired thermal insulation properties or meet the Building Energy Act (GEG).

In the construction of low-energy houses and passive houses as well as in energy / thermal renovation and modernization, thermal insulation plaster systems can further improve the insulating properties of the wall structure and the building materials used. However, they are not suitable as finishing plasters and decorative plasters, because the plaster surface must be protected from impacts.

Advantages of thermal insulation plaster:

  • water repellent
  • elastic and stretchable, therefore low risk of cracking
  • high thermal load capacity
Note: Since layer thicknesses of 5 cm or more are usually applied to thermal insulation plaster, it is advisable to hire a professional to apply the plaster to the wall using a plastering machine and spray nozzle.

Finished plaster and brush plaster

Mineral ready-to-use plasters are offered as textured plasters, rubbed plasters and roll plasters ("plaster off the roll"). In contrast to conventional dry mortars, the material is already pasty or ready to use. Because finished plaster is much heavier due to the water it contains, it is usually bought in smaller quantities and used for small areas and decors.

Mineral finished plasters consist of marble sand in various grain sizes and are often colored with mineral color pigments. When designing the wall, you can vary the color and color intensity with individual mixtures. Natural fiber plaster, cotton plaster, textile plaster and magnetic plaster (an intermediate plaster that makes the wall magnetic) are also offered as ready-made plasters.

A brushed plaster is a finished plaster that already contains wall paint and how it is painted on with a paintbrush, brush or roller. Different painting tools, painting patterns and product-specific mixing options create individual surfaces.

Synthetic resin plaster

Synthetic resin plaster (also: dispersion plaster) is a collective term for non-mineral wall and ceiling coatings that look like conventional plasters. They are used exclusively as finishing and decorative plasters and contain neither gypsum, lime nor cement. A polymer dispersion is used as the organic binder, combined with dissolved resin, a silicone resin emulsion or potassium silicate, depending on the type of plaster.

With a large selection of different grain sizes, colors and structures, dispersion plasters offer plenty of scope for artistic freedom and for implementing unusual design ideas. Synthetic resin plaster variants such as colored stone plaster are used, for example, to imitate marble surfaces, for pillars, columns or display walls.

A synthetic resin plaster is always delivered ready-to-use (pasty) in a bucket or silo and can then be processed by hand or with a machine. Before using the plaster, stir it thoroughly once more; minor adjustments to the consistency with solvent or water are also possible.

Advantages of synthetic resin plaster:

  • well suited for thermal insulation composite systems (ETICS)
  • good adhesion and durability on mineral substrates
  • very high mechanical resistance (abrasion, pressure and impact resistance)
  • Due to its variable elasticity, it is suitable for permanent crack bridging
  • can be integrated into ecological building concepts
Note: Synthetic resin plasters have only been used since the middle of the 20th century. Compared to lime, gypsum and clay plasters, which have been known for thousands of years, this plaster is a very young building material.

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