## 4 Findings  
### Laboratory Test--Natural Stone Specimens  
Laboratory tests were conducted on the durability of six types of limestone used in the exterior cladding of high-rise buildings and structures in the coastal zone of Israel from 1997-2016. The coastal zone of Israel is characterized by high average temperatures for most of the year, combined with high humidity and strong sea breezes affecting buildings and structures. In the exterior cladding made from five types of stones analyzed in this article, there was significant wear and tear within the first 2-4 years of building construction. As a result, property owners filed lawsuits against the contractors. The authors of this article prepared expert opinions on the compliance of all stones with Israeli standard SI 2378 Part 1 and the most likely reasons for the rapid wear and tear of the stones. The sixth type of stone was chosen as a reference since the exterior cladding of a 16-story building in the coastal zone proved to be highly durable. Three types of stones (marble, such as limestones no. 1, 2, and 6) were used as exterior cladding in pre-polished factory slabs. Three other types of stones were used as unpolished cladding stones with a rough natural texture. The physical and mechanical properties of four types of stones (three with a polished texture and one with a rough natural texture) fully complied with all requirements of Israeli standard SI 2378 Part 1. Two of the tested types of stones with a rough natural texture had water absorption exceeding the standard requirements; however, all other physical and mechanical properties fully complied with the standard requirements. In this article, we report only the results of the qualitative mineralogical composition, determined by XRD (X-ray diffraction) analysis, and standard tests of the capillary water absorption and the resistance to immersion of the stone samples (120 \(\times\) 120 \(\times\) 20 mm) for 24 h in a sodium sulfate salt solution (concentration 14%, by mass), followed by drying to a constant weight in a laboratory drying oven at a temperature of 102 \({}^{\circ}\)C \(\pm\) 2 \({}^{\circ}\)C. The samples were weighed on analytical scales before the start of the first cycle and at the end of each subsequent cycle. The stone test was stopped as soon as the weight of the sample decreased after drying at the end of the next cycle. Based on the changes in the sample weight, the critical content of crystallized salt causing stone crumbling was calculated. The test results are presented in Table 3 and in Figures 2-4. The results of the tests clearly demonstrate that the greater the capillary water absorption coefficient of limestone, the greater the critical sulfate content causing stone crumbling. However, no relationship was established between the capillary water absorption coefficient and the number of cycles during the crystallization test before the beginning of stone crumbling. For example, Limestone #1 (Hard) and Limestone #2 (Hard) began to crumble after the first and second cycles, respectively, just like Limestone #3 and Limestone #4. Although the capillary water absorption coefficient of Limestone #3 and #4 is twice as high as the maximum value allowed by the standard, the capillary water absorption coefficient of Limestone #1 and #2 is much lower than the maximum allowed by the standard. The reference stone (Limestone #6 (Hard)), which has the minimum capillary water absorption coefficient, began to crumble after the end of three cycles of testing. Similarly, Limestone #5 (Hard), whose capillary water absorption coefficient is 1.5 times lower than the maximum allowed by the standard, but almost 8 times higher than the reference stone (Limestone #6 (Hard)), began to crumble after the third testing cycle. Figure 2: Kinetic of stones’ weight changes during the crystallization test. Figure 3: Relationship between capillary water absorption and cycles elapsed before stone crumbling. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & &