Cementitious adhesives for tiles, which one to choose?

02/16/2021 – In the focus Adhesives for ceramic tiles, which one to choose? we talked about the types of glue to be used for ceramic wall and floor coverings.
Among these are the cementitious adhesives: available in the form of premixes, cementitious adhesives are produced in a wide range able to satisfy every need.

Preparation, which is done directly on site, is very quick. It consists of kneading the powder with water or with lattice elastomerico in aqueous dispersion. Using latex increases the impermeability, flexibility, adhesion properties and the ability of the binder layer to resist aggressive liquids and strong agents. The mixture with elastomeric latex is ideal for floors or coverings that will be subject to strong thermal excursions or where dimensional variations of the substrate are foreseen.

Cement-based adhesives are definitely very resistant and ensure a long life to the coatings. In fact, in addition to residential, they are suitable for rooms with a high concentration of humidity, for fixing coatings permanently immersed in water, as in the case of swimming pools, for industrial and commercial floors. Resistance comes from the fact that they are added in the mixture resin-based additives.

Based on UNI EN 12004 , which defines the “requirements, conformity assessment, classification and designation” of adhesives for ceramic tiles, cementitious adhesives can have one of the following performance classes in terms of resistance:

Class C1, normal adhesive (fundamental characteristics), possesses the minimum resistance values ​​required in all the required tests;
Class C2, improved adhesive (additional characteristics), it reaches higher resistances than those required by Class 1.

The indication of the Strength class is always mandatory, to this are added optional features:
quick setting cementitious adhesives (F), ideal for interventions that require rapid practicability;
slip resistant cementitious adhesives (T), ideal for wall coverings, especially if they are in large formats;
cementitious adhesives with extended open time (E). The open time is the period that passes between the application phase of the adhesive on the support and the moment when the mixture loses its adhesive properties. The longer the open time, the greater the chances of correcting small errors. Ideal for laying large formats, porcelain stoneware and glass type mosaics.

Another property of cementitious adhesives is the deformability, defined according to the standard UNI EN 12002. The deformability is the ability of the glue to compensate for the irregularities of the substrate and tiles. Generally with a standard, non-deformable glue, it is possible to level thicknesses up to 5 mm, a glue with deformability it also reaches 15 mm.

As a function of the deformation value, there will be:
– Class S1: deformable cementitious adhesives;
– Class S2: highly deformable cementitious adhesives.

From this overview it emerges that the characteristics to be considered are many, which are, therefore, the criteria to be considered for choose the most suitable cementitious adhesive?

The choice of cementitious adhesive must be made on the basis of the following criteria:
type of tile to be glued: porcelain stoneware, single-fired, double-fired, terracotta. Depending on the type of tile, the porosity of the same, or the ability to absorb water, consequently the type of cementitious adhesive to choose also changes.
tile size: big or small. At or above the 60×60 cm size, the tiles are defined as having a large size, below that with a small size;
type of coating: wall or floor, indoors or outdoors;
type of support: screed (cement, radiant) or existing floor (overlapping) or plaster;
mechanical and hygrometric stresses exercise; for example, it will be necessary to ask whether the coating will be subjected to bad weather, frost, thermal excursions or polluted agents. Or, if the cladding is intended for a commercial / industrial environment subject to a high load from foot traffic or vehicular traffic.

A Class C2 cementitious adhesive with improved adhesion is suitable for any type of tile but, if a C2 cementitious adhesive must always be chosen for porcelain stoneware, for single-fired or double-fired tiles it is also possible to limit oneself to a C1 adhesive, as long as the formats are not large.

When the use of the flooring is crucial for the continuity of the work inside the building, an adhesive with the letter F will be chosen.

If a wall cladding is installed, the slip resistance must also be sought, so the adhesive must be for example a C2T, i.e. improved adhesive with limited slip.

If you proceed with the overlapping installation, a C2TE adhesive, i.e. improved adhesive with limited slip, extended open time, is suitable for every type of tile that you decide to overlap.

If the rooms to be covered are large or the tiles have a particular format or in general “more comfortable times” are required for installation, it is necessary to choose cement-based adhesives with the letter E that allow for a longer workability time. With a C2 and a long opening time E double spreading can be avoided.

When laying large tiles (over 60×60 cm), it is important that a cementitious adhesive is used that has at least the deformability class S1. The same property must be sought when the substrate is not perfectly flat or is subject to slight dimensional variations.

Con i radiant screeds it is certainly advisable to choose cementitious adhesives that have S2 deformability.

Source: Edilportale.com by www.edilportale.com.

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