STONE RESTORATION part 5

STONE RESTORATION PRACTICE IN PALESTINIAN TERRITORIES:

A CASE STUDY FROM JERUSALEM

part 5

CONCLUSIONS

The results of this study show that the present practice of stone restoration in the Old City of Jerusalem is often inadequate, lacking especially any serious awareness of the considerations that should dictate the specific physical and mechanical characteristics of the stone and the patching/binding materials used. This consideration of the unique, specific needs of each individual structure – selection of the appropriate natural stone to be used for replacing missing or decayed ones and preparation of the proper mixtures for repairing or filling damaged areas, in addition to shapes and colors– is shown to be a realistic, manageable process that should be within the capabilities of local laboratories, using standard equipment and testing procedures. The results from the examination of the case study from Jerusalem illustrated that only through such custom-designed restoration processes it will be possible to upgrade the prevailing practice through according to standardized, measurable criteria, all the while preserving the materials’ authenticity as to their color and shape, insuring the utmost compatibility between the old and the new stones, and that they will hold up optimally in the future against the various deteriorative factors. This requires sufficient efforts for identifying the current condition of the stones to be restored, the causes behind their deterioration, and defining the appropriate criteria, within the practices prevailing in the country, for managing better maintenance and restoration process. Therefore, the basic concepts and testing methods  can be generalized, but not their specific application, because this will differ from one city, place, building (or even one building face) to another, according to the circumstances of each case: the location, the quality of the stone, and the surrounding environment. This requires special handling for each case in order to overcome the specific factors  causing deterioration. For example, Table (9) shows that the mix sample No. 4 has a density of 1.78g/cm³ (less density) and a water absorption ratio of 12.50% (higher porosity), which are compatible with the corresponding measurements for Old City stone samples Nos. 5 through 8 in Table (1). The same is valid for sample 6 in Table (9), which seems more appropriate to be used with the existing stone at Old City of Jerusalem sites 5 through 8 in Table (1). As for the replacement of stone to be used for those same sites, the lab results show that all stones- widely used at present in Jerusalem restorations- are inappropriate due to their extremely low water absorption ratio r higher density; and that for this application, the A’nata stone is a much better choice.

The same interpretation is valid for the use of the crushed stone and the silica sand in the proposed ratio (78%+ 22%) only with hydrated lime. In Table (9), the testing of the four samples prepared from these materials show an average density of 1.69g/cm³  and an average water absorption ratio of 14.75%, which are compatible with the same values for most of the existing stones at the Old City of Jerusalem sites (Table 1). Intensifying The re-use of the local crushed stone, promoting the manufacturing of the hydrated lime locally and minimizing the export of the silica sand,  are all factors that will have their positive impact on the local economy and will improve the quality of the restoration process. Furthermore, the hydraulic lime still has very limited application in Palestine due to the high market price and the lack of local know-how for its applications.

Concerning the white cement, all tests prove that it was used with the silica sand only to shorten the time of the hardening process, without having concrete impact on improving either the porosity or the density. Therefore, and considering its long-term decay mechanism, the white cement use in the restoration practice in Palestine have to be terminated.

This study has identified porosity as a very important factor in the process of restoration, given  because of its significant impact on the deterioration of the stonework in historic buildings. However it presents only one aspect of stone specifications, since the experiments which were conducted examined only the physical characteristics of the samples. It was impossible to conduct chemical analyses due to the lack of certain capabilities (for example, an x-ray machine and chemicals such as sulfuric acid and salt silica) as a consequence of the political situation in the country. In addition, it was impossible to do physical analysis for some materials, particularly measurement of the coefficient of thermal expansion of lime mixtures, or that of the original stone. These, however, should be considered as complementary tests: While they might contribute to optimal restoration practice, the lack of this analysis should not detract in any way from the results demonstrated here.

Finally and until today, no generally recognized laboratory standards for the materials used in carrying out stone’s restoration processes have emerged in Palestine. Thus, this study is a first attempt in this direction, toward the goal of standardizing the quality of the materials used in the restoration of old buildings, based on the available resources, and also their intelligent, differential use based on the specific conditions of a site. Furthermore, this study shows that there is a need for more studies on the wider philosophical and practical issues of restoration in the Palestinian old cities, because the present practice provides no control over what is done there and lacks serious responsibility for sites with very rich cultural significance.

....to be continue....