## 1 Introduction
\begin{table}
\begin{tabular}{l l l} \hline \hline \multicolumn{3}{c}{**Fundamental Characteristics**} \\ \hline
**Characteristics** & **Requirement** & **Test Method** \\ \hline \multicolumn{3}{c}{_Normal setting adhesives (C1)_} \\ \hline Initial tensile adhesion strength & \(\geq\)0.5 N/mm\({}^{2}\) & 8.2 of EN 1348 \\ Tensile adhesion strength after & \(\geq\)0.5 N/mm\({}^{2}\) & 8.3 of EN 1348 \\ water immersion & \(\geq\)0.5 N/mm\({}^{2}\) & 8.4 of EN 1348 \\ Tensile adhesion strength after & \(\geq\)0.5 N/mm\({}^{2}\) & 8.5 of EN 1348 \\ freeze-thaw cycles & \(\geq\)0.5 N/mm\({}^{2}\) & EN 1346 \\ Open time: tensile adhesion strength & \(\geq\)0.5 N/mm\({}^{2}\) & EN 1346 \\ \hline \multicolumn{3}{c}{_Fast setting adhesives (C1F)_} \\ \hline Early tensile adhesion strength & \(\geq\)0.5 N/mm\({}^{2}\) & 8.2 of EN 1348 \\ Open time: tensile adhesion strength & \(\geq\)0.5 N/mm\({}^{2}\) & EN 1346 \\ All other requirements as for normal setting adhesives (C1) & EN 1348 \\ \hline \multicolumn{3}{c}{**Optional characteristics**} \\ \hline
**Characteristics** & **Requirement** & **Test Method** \\ \hline \multicolumn{3}{c}{_Special characteristics_} \\ \hline Slip & \(\leq\)0.5 mm & EN 1308 \\ Extended open time: tensile adhesion strength & \(\geq\)0.5 N/mm\({}^{2}\) & EN 1346 \\ Deformable adhesive: transverse deformation & \(\geq\)2.5 mm and \(<\)5 mm & EN 12002 \\ Highly deformable adhesive: transverse deformation & \(\geq\)5 mm & EN 12002 \\ \hline \multicolumn{3}{c}{_Additional characteristics (C2)_} \\ \hline High initial tensile adhesion strength & \(\geq\)1 N/mm\({}^{2}\) & 8.2 of EN 1348 \\ High initial adhesion strength & \(\geq\)1 N/mm\({}^{2}\) & 8.3 of EN 1348 \\ after water immersion & \(\geq\)1 N/mm\({}^{2}\) & 8.4 of EN 1348 \\ High tensile adhesion strength & \(\geq\)1 N/mm\({}^{2}\) & 8.5 of EN 1348 \\ after freeze-thaw cycles & \(\geq\)1 N/mm\({}^{2}\) & 8.5 of EN 1348 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Requirements for cementitious (C) adhesives for ceramic tiles (CTA) according to EN 12004:2007+A1:2012 [10]. agreement between the results obtained by different analysts in different laboratories using a given measurement procedure. [PERSON] [13] described the results of initial adhesion tests of seven cementitious adhesives to ceramic tiles, carried out in ten laboratories using two different test concrete slabs. As the first test concrete slab, each of the participating laboratories used a standard test concrete slab that meets the requirements of EN 1323:2007 [14]. The second concrete slab was purchased by the research organizer and delivered to all participating laboratories. The standard deviation of the measurement ranged from 15 to 20%. As a result of the tests, the concrete slabs' influence on the value of the determined adhesion strength was found. For cementitious CTAs with a lower adhesion strength values, more considerable differences between individual measurements were made than for adhesives with higher adhesion strengths. In 2007, the Romanian laboratory, notified in the EN 12004, initiated a project of interlaboratory measurements of the initial adhesion strength of cementitious CTAs. Nine laboratories, mainly Romanian, participated in the first round of the research (2008-2009). Five years later, 27 laboratories of research institutes and producers of tile adhesives from the following nine countries--Austria, Bulgaria, Croatia, Czech Republic, Germany, Poland, Portugal, Romania, and Slovenia--took part in the interlaboratory tests [15]. Proficiency tests/interlaboratory comparisons were organized according to uniform principles and under the requirements of EN ISO/IEC 17043 [16]. The initial adhesion of four different cementitious CTAs (C2 FTE, C2 TES1, and C2 TS1) was tested. All laboratories used the same concrete slabs for tests and the same ceramic tiles provided by the test organizer.