Many different organic and mineral materials are available for plastering interior walls.
Depending on the product, interior plasters can be a high-quality finished wall surface or serve as a basis for further surface design, e.g. with paints, wallpaper or tiles. Interior plasters play a major role in regulating moisture indoors and thus in preventing fungal and mould infestation.
choosing the right interior plaster, the factors
must be taken into account together. In the case of plasters with mineral binders, the strength of the top plaster must not be greater than that of the base plaster, otherwise plaster cracks can occur.
In Section 6 (Planning), DIN EN 13914-2 contains numerous tips on the planning of interior plasters, including with regard to the factors influencing interior plaster systems, durability, acoustic properties, resistance to soluble salts, protection against X-rays, decorative surfaces, the thickness of the plaster layer on walls and ceilings, the types and designs of plaster surfaces and airtightness.
plaster thicknesses: The plaster thicknesses are specified in DIN18550-2 and DIN EN 998-1 and are:
In individual cases, manufacturers also specify different plaster thicknesses for their plaster systems, which are necessary due to physical requirements.
Aggregates and coatings: When applying a coating, the water vapour permeability of the coating must be matched to that of the interior plaster.
Initial coating of non-pigmented top coats: In the case of non-pigmented top coats, a coating in accordance with DIN 18363 must be applied, which usually consists of a base and final coat on the inside.
Initial coating of pigmented finishing plasters: In the case of pigmented interior plasters, an additional surface coating is usually not absolutely necessary. However, it is recommended by the manufacturers in many cases, as otherwise optical cloud formation can occur, e.g. due to calcium carbonate efflorescence or irregularities during application. In this case, one speaks of an levelling coating, see also "Leaflet on levelling coatings on noble plasters - colour-levelling coating".
Fire protection: Requirements for fire protection from building law or the property-specific fire protection certificate must be taken into account. For example, according to the Model Building Code (MBO), plasters in necessary stairwells (i.e. also in every apartment building with 3 or more residential units!) and in necessary corridors must be non-combustible. When choosing the interior plaster system, it is therefore important to pay attention to appropriate approvals.
Plaster as fire protection cladding: Many load-bearing and/or room-enclosing components, e.g. masonry walls, reinforced concrete columns or steel components, require plaster layers specified in DIN 4012-4 in order to meet their fire resistance class regulated in DIN 4012-4 or require a smaller component cross-section when plaster layers are taken into account. The requirements for the plaster layer for the respective component, e.g. with regard to reinforcement, plaster thickness, mortar group and detailed design, can be found in DIN 4102-4.
Sound-absorbing plasters (acoustic plasters): Acoustic plasters are used in particular when other measures are ruled out due to low installation heights. Acoustic plasters are assigned by the manufacturer to one of the six sound absorption classes according to DIN EN ISO 11654.
Renovation plaster: Recently, there have also been special renovation plasters for interiors with rapid readiness for covering. Similar to a rapid screed, the water contained in the plaster is bound crystalline. This allows the plaster for tiles to be ready for covering after just a few hours. For example, bathroom renovations can be carried out much more efficiently.
Renovation plasters: Renovation plasters are characterized by high porosity, low capillary water conductivity and high water vapor conductivity and are therefore particularly well salt-tolerant. A renovation plaster does not block off the substrate, but enables the controlled storage of salts, which neither visibly crystallize on the surface nor destroy the plaster. The determination of the necessary renovation measures is to be made by the planner, taking into account the leaflet E-2-9-04/D "Renovation plaster systems" from the WTA (Scientific-Technical Working Group for Building Preservation and Monument Preservation e.V.). When planning/determining the specific remediation measures, the cause of moisture must be clarified in advance, the water-soluble salts must be determined and the type and condition of the plaster substrate must be examined. In the case of very high salt load on the substrate, it may also be necessary to temporarily apply a sacrificial plaster for desalination, which absorbs the existing salts and is then replaced by the final plaster.
Plaster reinforcements: Plaster reinforcements can significantly minimise the risk of plaster cracks, but cracks in the plaster layer due to component deformations of the plaster substrate (e.g. as a result of deflection, settlement, temperature deformation) cannot be prevented by reinforcement measures . Therefore, e.g. movement joints of the building must also be included in the plaster layer.
Plaster reinforcements usually consist of grids or fabrics made of plastic, mineral fibres or metal. They must be installed as close as possible to the finished plaster surface, with 100 mm of overlap and at least 200 mm of overlap on adjacent components on the overside.
In the case of increased stress, it may also be necessary to apply a reinforcing plaster with a full-surface fabric insert as an intermediate layer between the base and top plaster in order to prevent cracking. Increased stresses result from the substrate (e.g. existing cracks/ moisture load or irregularities due to material changes/ built-in parts/ mixed masonry/ natural stone masonry, cracked plaster substrate). In the case of (single-layer) plasters containing gypsum, the reinforcement layer is placed between two wet-on-wet plaster layers.
Substrate pretreatment: the substrate must always be dry, clean and load-bearing. When using plasters containing gypsum, the substrate residual moisture of normal concrete must not exceed 3% (mass fraction).
Any release agents present on concrete surfaces, e.g. formwork oils, must be completely removed, as well as cement haze or glassy sintered skin. Open joints and slits must be closed, and larger unevenness must be compensated for. The need for additional substrate pre-treatment depends in particular on the absorbency of the substrate, which must be uniform and neither too strong nor too weak
[...]
Due to the manufacturing process, the absorbency of some substrates fluctuates greatly, e.g. in the case of sand-lime brick, so that this should also be checked in a new building before the plastering work begins.
According to VOB Part C, in this case DIN 18350 (plastering and stucco work), the executing contractor is obliged to inspect the subsoil accordingly before starting his work and, if necessary, to register any concerns about execution (without additional measures). All the substrate pre-treatments listed are special services for which the contractor may be entitled to separate remuneration. As far as can be seen in advance, corresponding items should therefore be included in the tender specifications in order to arrive at a price agreement in this regard at the time of awarding the contract.
Interior plaster profiles: There are suitable special profiles for the large number of possible applications:
Common materials are galvanized steel, stainless steel, aluminum and rigid PVC. Plaster profiles are fixed in the final layer with mortar chunks before the first layer of plaster is applied. The mortar blocks must be made of the same material as the first layer of plaster or of cementitious mortar. If metal pins and nails are also used for fixation, they must always be completely removed before applying the first layer of plaster. According to the "Leaflet on substrates in damp rooms", stainless steel profiles must always be installed in damp rooms. Only in domestic kitchens and bathrooms are other materials possible, but no galvanized steel profiles.
Weather conditions: The manufacturer's specifications must be taken into account. As a rule, plastering work may only be carried out at temperatures between 5 °C and 30 °C without special protective precautions. In the case of silicate plasters, manufacturers often specify higher minimum temperatures, e.g. 8° C. Not only the air temperature is affected, but also the surface temperature of the substrate and the processing temperature of the plaster mortar. This may require additional heating in appropriate weather. Strong direct sunlight and draughts can also be avoided during processing without protective measures.
Drying time: Before further coating of interior plaster surfaces, a minimum service life of one day per mm of plaster thickness must be observed. If the plaster substrate is soaked or at low temperatures, the service life is further extended. When carrying out a reinforcing plaster, an additional service life of at least 7 days must be taken into account. In any case, it is important to ensure sufficient room ventilation during drying.
Maintenance and repair: DIN EN 13914-2 contains numerous tips on the maintenance and repair of interior plasters in Section 8 (Maintenance and repair - except restoration), including with regard to efflorescence and the repair of cracks.
DIN 4102-4, Fire behaviour of building materials and components; Compilation and application of classified building materials, components and special components
DIN 18157-1, execution of ceramic cladding in the thin-bed process; Hydraulically hardening thin-bed mortars
DIN 18350, VOB Part C, General Technical Terms and Conditions for Construction Services (ATV) Plastering and stucco work
DIN 18550-2, Planning, preparation and execution of interior and exterior plasters Part 2: Supplementary specifications to DIN EN 13914-2 for interior plasters
DIN 18558, synthetic resin plasters; Definitions, requirements, execution
DIN EN 998-1, specifications for mortars in masonry construction - Part 1: Plaster mortars
DIN EN 13914-2, planning, preparation and execution of interior and exterior plasters - Part 2: Interior plasters
DIN EN 15824, specifications for exterior and interior plasters with organic binders
DIN EN ISO 11654, Acoustics - Sound absorbers for use in buildings - Assessment of sound absorption
Guideline for the plastering of masonry and concrete - Basics for planning, design and execution, Publisher: Industrieverband WerkMörtel e.V.
Leaflet E-2-9-04/D Renovation Plaster Systems, Publisher: WTA (Wissenschaftlich-Technische Arbeitsgemeinschaft für Bauwerkserhaltung und Denkmalpflege e. V.
Leaflet on substrates in damp rooms, Publisher: Department of Finishing in the Central Association of the German Construction Industry, Berlin
Leaflet for planning and application of metallic plaster profiles in exterior and interior; Publisher: European Association of Plaster Profile Manufacturers
Technical Data Sheet TM 01: Requirements for clay plasters as a component; Publisher: Dachverband Lehm e.V.
Source: bauwion
