Moisture induced length changes of tile adhesive mortars and their impacton adhesion strength 2017-04-17

tile adhesive

  1. Miroslav
    1. Introduction
    Ceramic tiling is commonly used in various application fields inside buildings or at the exterior like external cladding of facades, floor covering as well as for swimming pools. A tiling consists of ceramic tiles, which are fixed generally with a polymer-modified cementitious adhesive mortar to the substrate, e.g. concrete. The joints between the tiles are usually filled with a joint grout. A key issue to use ceramic tiles is besides aesthetic aspects their gen-erally low water absorption, providing a high durability. The trend to use fully-vitrified, large-sized stoneware tiles has increased in the recent years [1]. Due to their low porosity and water absorp-tion of less than 0.5 wt.% they are frost resistant and thus recom-mended for the application in the outside area. The large formats are applied for mainly aesthetic reasons.

    However, technical problems appear which are related (i) to higher shear forces upon deformations due to the large size of the tiles [2] and (ii) poor adhesion of the cementitious adhesive mortar on the vitrified surface of the tile. As a consequence, an increasing amount of damages like adhesion failure of wall tiles or cracking of the tiles are reported [3–5]. These problems lead to increasing requirements concerning the properties of a tile adhesive and to the application process [1,3,4,6,7].

    The climatic conditions (moisture, temperature) increase the complexity of the system, because they are varying during daily and yearly cycles. They may also vary within a tiling or even from substrate to tile and, especially in the case of large tiles, from rim to center of the individual tile. The local conditions cause mois-ture and hydration gradients across and parallel to the mortar bed [8–11]. The gradients influence the hygrical and thermal shrinkage and expansion behavior, initiating micro-cracks prefer-entially at the edges of the tiles, where the highest shear stresses between tile and adhesive mortar occur [7,11–13]. Those shear stresses may cause a delamination of the tile at this position, lead-ing to a poor or even a complete loss of adhesion. Especially in exterior application, stresses induced by the weathering condi-tions may cause a more rapid progress of failure development [9,11,14–17].