This problem mainly concerns floor coverings. As a rule, the occurrence of such a defect is characterized by a so-called “incubation” period, during which some tiles separate from the base. At the initial stage of such a defect, the tiles remain attached to each other thanks to grouting. However, when tapping in some areas, sometimes quite large, a characteristic squelching sound is heard, which means that the tiles are separated from the sub-cladding structure (such an empty sound is often heard when walking on the floor).
At the initial stage, a slight sagging of the floor may be observed. At first, this effect is not very noticeable; it can be replaced if, for example, the door begins to touch the floor, or the furniture is uneven. Finally, the deflection reaches such proportions that entire parts of the tiled surface are separated, completely destroying the adhesion of the floor structure and the stability of the system as a whole. There are two fairly typical circumstances that must be taken into account when determining a defect and establishing the causes. First: an absolutely clean back surface of the tile indicates that the adhesion failure occurred precisely at the point where the tile was attached to the base. Second, the size of the floor surface from which the tile has separated is smaller than the tile itself, so the tile cannot be laid back on the surface. Obviously, the consequences of such a defect are completely functional, since the integrity of the lined surface is compromised.
Cause of the defect
The very nature of this pathology indicates a state of dangerous compression of the facing surface parallel to the surface plane. The tiles are compressed, which puts pressure on the bond between the tile and the base, which in some places reaches such a force that it breaks this bond. Thus, the process of separating the tiles from the base begins. Gradually, the load reaches its “peak” value and affects the tile, which in turn separates perpendicular to the surface on which it was laid. The result is complete separation of the facing surface from the base. So, what could be the reason for this effect? The reason is usually associated with a reduction in the surface of the base due to such a phenomenon as shrinkage of the building as a whole. The higher the loads acting on the facing layer, and, consequently, the risk of such a defect occurring, the more limited the mobility between the different layers (especially between the facing layer and the base), the higher the elastic modulus (i.e., the higher the rigidity ) layers of the structure, especially the facing layer.
Many of the phenomena that give rise to such stresses relate to the physiological characteristics of certain materials. It is normal for materials to change in size due to temperature changes, just as it is normal for lime and cement conglomerates to contract during hardening, a process that can take quite a long time (up to two years). Naturally, some structures are less rigid due to the constituent materials and dimensional characteristics. Thus, the quality of the tile cannot cause such a defect unless it can be stated that the coefficient of thermal expansion and swelling of the tile is unusual or does not meet the requirements agreed upon in advance, or the building has undergone abnormal shrinkage due to the formation of cracks, damage, etc.
The crux of the problem lies in the planning and design of the floor structure, which must be based on a thorough knowledge of the materials used and clear criteria for installing the system. It is useful to remember that a floor or wall structure is a collection of different materials interconnected in such a way that these relationships affect the materials and the loads acting on one material are transferred to other components of the system. Indeed, in most cases, a defect arises as a result of an error made at the planning and design stage. In this case, as discussed in previous chapters, it is very difficult to clearly identify one cause. As a rule, the reasons are different and interact in such a way that “risky” design decisions lead to the formation of a defect, however, they are not the only reason for its occurrence. Here are examples of such “risky” design decisions:
- Absence of expansion joints around the perimeter and inside the large veneered surface;
- The use of closed joints leads to an increase in surface rigidity;
- Laying tiles on a thin layer of cement-based adhesive mortar (hence rigid), directly on a supporting structure characterized by high mobility and deformation;
- Premature laying of tiles, without proper separation of layers, on insufficiently hardened cementitious structures that are still in the compression stage.
The consequences, as a rule, are worse, the more severe the operating conditions of the surface (for example, external surfaces subject to temperature changes, public and industrial premises subject to intense mechanical loads). The actual laying of the tiles is also of great importance, however, the laying alone cannot be the cause of such a defect. Obviously, such a defect can be, if not prevented, then at least limited or delayed if the base under the tile is carefully installed in terms of density and uniformity, as well as the flatness of the facing layer.
Prevention
Naturally, the most effective measures to prevent the occurrence of such a defect can be taken at the planning and design stage. Among them:
- Pay special attention to the location, size and correct arrangement of expansion joints;
- If possible, use open seam installations as they reduce the risk of this defect forming;
- You should not lay tiles directly on flexible or moving surfaces, using mechanically rigid adhesive solutions, for example, cement-based ones.
In these cases, it is worth using adhesive solutions based on organic substances with appropriate elastic and plastic characteristics, and it is also necessary to install a separating layer between the floor and the underlying structure (“floating floors”). In any case, it should be remembered that this reduction in stiffness not only prevents or reduces the transfer of loads from the sublayer to the floor, but also reduces the interaction between these layers and the floor itself.
The article was based on the following materials:
“How and Why” by Timellini Giorgio and Palmonari Carlo.