Mortars and adhesives for tiles

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Special mortars and adhesives are used to permanently attach tiles and slabs to walls and floors .

In the past, the tiles were fixed with thick lumps of mortar (thick bed method). Today, thin-bed mortars are used almost exclusively. The adhesive is applied to the substrate, combed with a notched trowel or a toothed smoothing trowel and then the tile is inserted. The larger the tile, the larger the teeth on the smoothing trowel.

Different tile adhesives are used depending on the substrate or area of ​​application.

materials

Different mortars and adhesives can be distinguished depending on their composition.

Cementitious mortars

The building materials industry offers a wide range of cement-based mortars that are suitable for laying tiles. Basically, a distinction can be made between mortar with and without additives and other special forms.

Cementitious mortar without additives

Cement-containing mortars without additives are rigid in the hardened state and are therefore only suitable for cladding unplastered wall surfaces using the thick bed method . A so-called mortar is used , which consists of cement , the aggregate (usually sand with a grain size of 0 to 4 mm) and the mixing water . The mixing ratio of cement to aggregate is between 1: 4 and 1: 8 and must be matched to the existing subsoil and the covering material. The components are mixed on the construction site and then processed directly. The setting mortar hardens through a hydraulic rearrangement and forms a firm connection between the substrate and the covering material.

Cementitious mortar with additives

additive effect
Methyl cellulose water-retaining
Starch ether water-retaining
Air entrainer Increase in suppleness and productivity
Fruit acid Delay in solidification
Lithium carbonate Acceleration of the solidification
Plastic powder dispersion Adhesion improvement
Metal soap Generation of water-repellent substances when solidifying

Finished walls and floors are usually clad using the thin-bed or medium- bed method . However, since the mortar thickness in these two methods is significantly thinner compared to the thick-bed method, additives must be added to the mortar. These additives primarily have a water-retaining and elasticizing effect. The dry mortar arrives at the construction site already mixed, mixing water is then added and is used after a short maturing period. The hardening time is about one day.

Special forms of cementitious mortar

  • Fast- hardening cement adhesives (also called fast- acting adhesives ) can be grouted after a few hours and fully loaded in a few days.
  • Cement-containing thin-bed mortars with a particularly high plastic coating (also referred to as flexible mortar or flexible adhesive ) have, in the solidified state, increased deformability and improved structural and bond strength. With these properties, the flexible mortar is suitable for surfaces outdoors, with low water absorption of the substrate (e.g. old ceramic flooring) or the covering material (e.g. fine stoneware) and for substrates that are slightly deformed ( e.g. heated screeds or dry screeds ). In frost, permanently wet and underwater areas, however, two-component flexible mortar should be used that meet the S2 standard in accordance with DIN EN 12002. One-component, "flexible" thin-bed mortars are mostly unsuitable here due to the nature of their plastic coating. DIN EN 12004 (including the deflection according to DIN EN 12002) and the leaflet “Flexmörtel” from the Association of the German Tiling Industry are available for classifying flexibility.
  • Fluid bed mortars contain a synthetic resin dispersion which has a particularly water-retaining effect and also has an organic adhesive effect. With these properties, the fluid bed mortar is suitable for laying particularly dense covering materials (such as fine stoneware).
  • Because normal thin-bed mortar can discolour natural stone and marble if improperly processed , there are special cement mortars for this purpose. One cause of the discoloration is the porosity of the natural stone slabs, through which the components of the cement mortar diffuse to the visible surface and become visible there. When using notched trowels to apply the adhesive, an annoying stripe pattern can arise. As an alternative to special mortars, it is often sufficient to cover the back of the natural stone slab with a thin layer of adhesive before it is placed in the combed mortar bed. In addition, the stone's own components can be activated by the mixing liquid and / or the alkalinity of the mortar (e.g. rusting iron ores) or the natural stone slabs tend to "break up" due to the one-sided water pollution of the wet mortar. We therefore recommend the use of natural stone thin-bed mortars, which are characterized by high and rapid crystalline water binding. White natural stone adhesive mortars are also recommended for translucent (translucent) natural stones.

Dispersion adhesives

Dispersion adhesives consist of a mixture of organic binders in the form of aqueous polymer dispersions (mostly vinyl acetate or acrylic resin ), organic additives and mineral fillers. The components are mixed ready for use and can be processed directly. The evaporation of the water causes the dispersion adhesive to harden.

In comparison to the other thin-bed materials, dispersion adhesives are rarely used. Due to their sensitivity to water, dispersion adhesives are only used indoors (outside of wet areas) and only on walls because of the long curing time. Dispersion adhesives are particularly suitable on smooth surfaces such as rigid foam boards or old tiles. Moisture-sensitive substrates (such as plasterboard ) must be pretreated.

Reaction resin adhesives

Reaction resin adhesives are single or multi-component thin-bed materials. They usually consist of a synthetic resin as a binding agent, the hardener and mineral fillers. The components are mixed on site and then processed. The curing takes place through a chemical reaction of the components.

Depending on the type of binder, a distinction can be made between epoxy resin adhesives and polyurethane adhesives . After curing, epoxy resin adhesives are relatively rigid, completely water-resistant and chemically resistant. The addition of polysulfides means that epoxy resin adhesives remain flexible after curing. Polyurethane adhesives are highly flexible, water and frost resistant and are very suitable for difficult substrates made of plastic, glass or metal. However, due to the high material costs, polyurethane adhesives are rarely used.

Casein tile adhesive

The tile adhesive consists of casein , hydrated lime and additives . The adhesive strength is achieved through the alkaline digestion of the casein proteins.

processing

Basic terms

  • Pot life / processing time: Maximum time for processing the mortar or adhesive after mixing.
  • Maturing time: Required rest time for cementitious mortar after mixing.
  • Open time: Maximum period of time after applying the mortar or adhesive on the substrate until the covering material is embedded while maintaining the required tensile strength.
  • Wetting ability: ability of the applied mortar or adhesive to wet the back of the tile or slab.
  • Correctability: Maximum period of time in which an already embedded tile or plate can be corrected in its position without a significant reduction in the adhesive tensile strength.

Health hazards

Tile adhesive was reinforced with asbestos fibers until the mid-1980s to increase the stability of the bond. Nowadays, asbestos fibers can be released especially during renovation work, for example when tiles are removed during renovation work in the bathroom or kitchen. Measurements by the Swiss Accident Insurance Institute showed that, for example, sanding off the old tile adhesive can release up to one and a half million respirable asbestos fibers per cubic meter, so that not only the health of the worker is endangered, but also the surrounding rooms are presumably heavily contaminated. Before renovating or working on older bathrooms or kitchens, the applied adhesive must be tested for harmful substances.

Norms and standards

  • DIN EN 12004-1 and 12004-2 Mortars and adhesives for ceramic tiles, parts 1 and 2

literature

  • Friedemann Enßle: Building technology learning field. Tile, slab and mosaic layers . Verlag Handwerk und Technik, 2009, ISBN 978-3-582-03588-2 .

Individual evidence

  1. Plasters containing asbestos, leveling compounds and tile adhesives: a new problem? Presentation by BG Holz und Metall, accessed on August 21, 2019.
  2. ^ Asbestos-containing plasters, fillers and tile adhesives in buildings . Presentation of the General Association for Pollution Control, accessed on August 21, 2019.