STONE RESTORATION part 6

STONE RESTORATION PRACTICE IN PALESTINIAN TERRITORIES:

A CASE STUDY FROM JERUSALEM

part 6

REFERENCES:

1        Ghadban, Sh. Traditional Architecture  in Palestine, Encyclopedia of the History of Science, Technology, and Medicine in Non- Western Cultures, Helaine Selin, ed. 2nd edition. Berlin: Springer Publishers, 2008, pp. 225-238.

2        Rangaswamy, R. ‘Jerusalem Stone- Natural Beauty and Tradition’,  http://ezinearticles.com/?Jerusalem-Stone---Natural-Beauty-and-Tradition&id=3524207,       Last Accessed 01/07/2011.

3        Cohen, S. Jerusalem Undivided, New York: Herzl Press, (1980).

4        Khamaisi, R. ‘Old City of Al- Quds/ Jerusalem: Challenges for an Administration of Urban Function’, Al- Quds/ Jerusalem 2015 Program- 2008 Report, Research Center for Islamic History, Art and Culture (IRCICA), Organization of the Islamic Conference, Istanbul, Turkey, pp. 1-35, (2009).

5           Laurent,  B. and Riedlmayer, A. ‘Restorations of Jerusalem and the Dome of the Rock and Their Political Significance, 1537- 1928’ Journal of Muqarnas, , Vol. 10, Essays in Honor of Oleg Grabar, 1993, pp. 76-84. http://www.jstor.org/stable/1523174,  Last Accessed 24/10/2010.

6        Rangaswamy, R. ‘Jerusalem Stone- Natural Beauty and Tradition’,  http://ezinearticles.com/?Jerusalem-Stone---Natural-Beauty-and-Tradition&id=3524207,       Last Accessed 01/07/2011.

7        Ghadban, Sh. ‘Typology and Composition of the Traditional Palestinian House’. Proceedings of the 10th Conference on Vernacular Architecture Alps Adrea – Ten Years of Efforts, (2000), P.71,  Full text is available at http://www2.arnes.si/aa/. Last Accessed 04/07/2011.

8        Arnon, A., 1992. ‘The Quarters of Jerusalem in the Ottoman period’, Journal of Middle Eastern Studies, Vol.  28, No. 1, January 1992, pp. 1-65.  http://www.jstor.org/pss/4283477,  Last Accessed 25/05/2011.

9        Khamaisi, R. ‘Old City of Al- Quds/ Jerusalem: Challenges for an Administration of Urban Function’, Al- Quds/ Jerusalem 2015 Program- 2008 Report, Research Center for Islamic History, Art and Culture (IRCICA), Organization of the Islamic Conference, Istanbul, Turkey, pp. 1-35, (2009).

10    Honeyborne, D. Weathering and Decay of Masonry, in Conservation of Buildings & Decorative Stone, ed., Ashurst J.& Dimes Fr., Butterworth Heinemann Publishing (1998), p. 153.

11       Zagari, M. Biology of Restoration, Italia- Jordanian Cooperation Project, Ma’daba School for Mosaics, Al- Dustur Al- Tijariah, Amman, Jordan (1998), pp. 98- 103. (In Arabic)

12    Camuffo, D., Del Monte, M., Sabbioni,  C. and Vittori, C.. Wetting, ‘deterioration and visual features of stone surfaces in an urban area’, Journal of Atmospheric Environment, Vol. 16, Issue 9, ….1982, pp. 2253–2259.

13    Camuffo, D., Del Monte, M. and Sabbioni C., ‘Origin and growth mechanisms of the sulfated crusts on urban limestone’, Journal of Water, Air and Soil Pollution, Vol. 19,…. 1983, pp. 351–359.

14    Bonazza, A., Messina, P., Sabbioni, C., Grossi, C. M. and Brimblecombe, P., ’Mapping the impact of climate change on surface recession of carbonate buildings in Europe’, Journal of Science of the Total Environment, Vol. 407, Issue 6, March 2009, pp. 2039-2050.

15       Rothert, E., Eggers, T., Cassar, J., Ruedrich, J., Fitzner, B. & Siegesmund, S. ‘Stone properties and weathering induced by salt crystallization of Maltese Globigerina Limestone’, Geological Society, London, Special Publications, Vol. 271; 2007, pp. 189-198; http://www.stone.rwth-aachen.de/download.htm, Last Accessed 30/06/2011.

16       Smith, B., Gomez-heras, M. and Viles, H.. Underlying Issues on the Selection, Use and Conservation of Building Limestone, Geological Society, London, Special Publications, Vol.  331, 2010, pp. 1-11,

http://sp.lyellcollection.org/cgi/content/abstract/331/1/1, Last Accessed 30/06/2011.

....to be continue..

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....

STONE RESTORATION part 4

STONE RESTORATION PRACTICE IN PALESTINIAN TERRITORIES:

A CASE STUDY FROM JERUSALEM

part 4

Porosity Test of the Hand-made Mixtures

The same method was applied to determine the density (dry & bulk) and the optimum absorption ratio for hand-made mixtures prepared by using various combinations of materials: crushed stone, silica sand, hydrated lime, hydraulic lime, and white cement. The main intention is to test the compatibility of these mixtures in terms of porosity with both the existing stones and the new stones to be used for the restoration works. For this purpose, a sieve analysis is conducted for: (1) the crushed stone obtained from the area of A’nata due to the results of the porosity analysis obtained and shown  in Table (3); and (2) for the silica sand. The aim of these tests is to determine the appropriate particles size for use in all samples that will be subjected for lab testing. For this purpose, procedures were as follows:

-          460 gr. of crushed stone was washed with water and then dried in an electric oven for 24 hours.  It was re-weighed after drying, yielding a reading of 390 gr. The sample was then put in a sieve (No. 200) and shaken in a mechanical shaker for 10 minutes. The results of this are shown in (Table 3) and (Fig 5), and they quantify the gradation of particle sizes within the sample of crushed stone which was used.

-          360 gr. of silica sand was washed with water and dried in an electric oven for 24 hours. It was then re-weighed after drying, showing then a weight of 300 gr. Then it was put in a sieve (No. 200) and shaken in a mechanical shaker for 10 minutes. The results are shown in (Table 4) and (Fig 6), and they show the gradation by particle size of the sample of the silica sand which was used.

The lab tests were performed in 3 groups in accordance with the materials being used to prepare the mixtures for testing. The ingredients for each group were mixed in different proportions by volume. Then the mixtures were placed in plastic containers after adding adequate amount of drinking water. Each of the wet mixture samples was then poured into a mold which had been numbered and exposed to the natural atmosphere in the laboratory. After allowing one week for drying, the porosity of the samples was measured, as follows: the hardened samples were completely saturated with water; the weight and volume of each sample was measured; the samples were dried in an oven at 105º C (±5º C) for 24 hours; after drying, each sample was weighed; finally the weight of the lost, evaporated water was calculated. The volume of each mixture was obtained through variable units by volume for each of the materials being used in the preparation of the samples for testing. The results are shown in Tables (7 to 9), with the porosity expressed as an absorption ratio. The three groups for lab testing are as follows:

-          Seven samples were prepared using various combinations of fine crushed stone, hydrated lime paste and white cement (Table 7). The first 4 samples in this table provide the results of various mixes of fine crushed stone with hydrated lime paste, which historically, presents the oldest building hand-mixtures used for construction purposes in the country. At that time, the stones were obtained locally, crushed to reach the necessary gradation and then mixed with hydrated lime, grog and/ or ash to obtain the desired homogeneity and hardening. During the testing of these 4 samples, the observations stated a slight slowdown in the process of hardening of the mix. Thus, the other 3 samples were prepared by adding white cement- used widely in the present restoration practice- to the mixture. As a result, the process of hardening became faster, but no significant deviation have been observed either in the absorption ratio or the density (Table 7).

-          Then, ten samples were prepared using different combinations from: silica sand, hydrated lime paste white cement and hydraulic lime (Table 8).  The use of silica sand for construction purposes in the Palestinian territories dated back to the intense European influence at the end of the nineteenth century and first decades of the twentieth century- colonial settlement movement and the British Mandate. At that time, the Portland cement started being introduced in the various building activities, and the use of silica sand obtained from the coastal area of Mandate Palestine turned into a popular practice in the preparation of the concrete material. Gradually, the silica sand replaced the fine crushed stone and turned out to be a basic component mixed with lime paste and a very small amount of stone’s powder, grog or ash, for the preparation of different filling mixtures applied in the building construction including in the restoration practice. After the division of Mandate Palestine into two states (in 1948), the  Gaza and the coastal area of the Mediterranean became inaccessible for the residents of Jerusalem and the silica sand started being brought from the region of Swelyh/ Jordan.

The first 3 samples in table (8) show the results of the lab tests of mixtures from silica sand and hydrated lime paste. The observations show that there was a visible slowdown in the hardening process of these 3 mixtures and that more than one week were necessary to obtain the desired hardening. Thus, in the samples from 4 to 6, the white cement- which replaced the stone’s powder, grog or ash at a later stage around the mid of the twentieth century- was added to the silica sand and the hydrated lime. Furthermore, in samples from 7 to 10 the hydraulic lime- still not widely applied in Palestine-  replaced the white cement. Again in this group, the process of the hardening became faster in the samples from 4 to 10, but no significant deviations have been observed either in the absorption ratio or in the density (Table 8).

-          The third group of laboratory experiments has to test a possible blend between the crushed stone and the silica sand considering the following three issues: (1) the crushed stone material is available at ample amounts in the Palestinian territories and it can easily be obtained at fine quality and reasonable prices. (2) There is a plenty of wastes from the stone industry in Palestine that can be re-used through possible future manufacturing of the hydrated lime, and (3) after the establishment of the Palestinian National Authority in 1994, it became more difficult to acquire the silica sand in adequate quantities, good quality and reasonable prices, due to the mobility restrictions imposed by the Israeli authorities.  For these reasons, it was decided to test different samples obtaining a mixture of 78% crushed stone to 22% silica sand, hydrated lime paste, hydraulic lime and white cement (Table 9).

This proportion between the crushed stone and the silica sand is based on the results of the sieve analysis from Tables (3 & 4) that allow the characteristics of the two materials, crushed stone and silica sand, to be identified.  The next step was mixing the two materials together using various proportions (by weight), starting with 90% crushed stone to 10% sand and reaching finally the ratio of 50% each of the two materials. The ultimate aim of this step was to find the optimal ratio for mixing the crushed stone and the sand. The results of the sieve analysis of the various mixtures are shown in (Table 5), and the data from the final column were used to produce the diagram in (Fig 7a). That in turn allowed the researchers to make a comparison between the conducted sieve analysis of these two local materials and the criteria established by the ASTM C136 - 06 Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates, shown in (Fig 7b). By comparing the two diagrams in Figure (7), it was noticed that the gradation of the tested ratios of mixing crushed stone with silica sand corresponded adequately to the standards accepted internationally. So, the next step was  to test the optimal density of the mixed materials using the ratios stated in Table (5) (but neglecting the ratios 60/40 and 50/50, since they were far from the accepted standards). The results expressing the optimal density are shown in Table (6) and the diagram drawn in Figure (8). The curve shows that the optimal density of the mixture is approximately 78% crushed stone to 22% sand. It is worthy to mention that the use of silica sand will minimize the quantity of water needed to prepare the mixture. Yet, the presence of the silica will help more for better cohesion of the mixture.

After determining the optimal crushed stone-sand density, 11 mixture samples were prepared  using this optimal (78/22) stone-sand mixture. In  samples 1-4 only the hydrated lime paste was added, in samples 5-8 the hydraulic lime replaced the hydrated lime paste and in the last samples from 9-11 the white cement was added to the stone-sand mixture and the hydrated lime paste. During the lab tests, the observations stated a normal and acceptable process of hardening of all samples. but again, no significant deviations have been observed in the average sums either of the absorption ratio or the density (Table 9).

The results of the lab tests in the three groups show that all samples retain absorption ratios higher than those for the stones from the buildings in the Old City of Jerusalem. The same elucidation  is valid for the density, which draws closer to the density of the stones in these buildings. These are good indicators, as the Common practice is the new stones and the mixtures better being more porous and less dense than those existing ones (Table 10). The only problem was related to the hardening time needed for each sample. This process of hardening accelerates or slows down according as the materials used to prepare the various mixtures. In this context, the weaker results were obtained from mixing the silica sand only with hydrated lime. This fact explains the still prevailing practice of using the white cement in the present restoration activities in Palestine, to accelerate the hardening process without encountering the future negative consequences of this practice on the quality of the restoration. Yet, the blend between the crushed stone and the silica sand proved to be an excellent alternative to the present practice, and have its potential towards the economic development in the fields of the local stone industry.   

Other two major issues were encountered during the laboratory tests:  the difficulty of controlling the amount of water added or lost in the mixtures, especially the water in the hydrated lime; and the quantity of soft material that was accumulated in the No. 200 sieve, which was around 15% instead of the 5% allowed under international standards. Both problems affect the accuracy of the results in general, however they don’t argue against the appropriateness of the methodology that was used.

...to be continue.... 

STONE RESTORATION part 3

STONE RESTORATION PRACTICE IN PALESTINIAN TERRITORIES:

A CASE STUDY FROM JERUSALEM

part 3

LABORATORY EXPERIMENTS

The aim of the laboratory experiments, which were conducted in the laboratories of the Department of Civil Engineering at Birzeit University, was to determine the density and the optimum absorption ratio which would cause all components used in the restoration process– existing on-site building stones; new stones imported from different sites and the materials mixed- for binding, patching/filling and sealing of masonry– to all interact with and complement each other. The following experiments were conducted:

-          Porosity test for: stones in use in existing buildings and for the new stones to be used in restoration obtained from the local quarries.

-          Sieve analysis of the crushed stone and the silica sand that will be used for preparing the various mixtures for lab testing.

-          Porosity test of a variety of mixtures (crushed stone, silica sand, hydrated lime, hydraulic lime and white cement), to be used in further testing. The introduction of the white cement into the laboratory experiments is done just because it was used in the restoration of most of buildings mentioned beforehand in this paper and in order to test the impact of this material within the locally prevailing restoration’s practice.

The above-mentioned experiments were conducted using material samples that were selected as follows:

-          Stone pieces extracted from the buildings inside the Old City of Jerusalem, and from the several quarries that provided and still presently provide stones for the restoration activity in Jerusalem.

-          Silica sand, which is usually brought by trucks from the Palestinian coast in Gaza or from Israeli sites like Ashdod, Askelon and Dimona. Lab tests conducted by the Geotechnical and Material Testing Center (GMT) in Ramallah/ Palestinian Territories, over the past five years have demonstrated that this sand has a light salt content as well as organic impurities. Still, the present practice is to soak the sand in water and wash it carefully before using it in the restoration process.

-          Crushed limestone, which is crushed in special stone crushers. The crushed stone available on the local market contains a high percentage of fine particles, however, exceeding the percentage permitted nationally and internationally. To remedy this, a visit to the crushed stone manufacturers in Al-Ram (a village north of Jerusalem) allowed the researchers to obtain a more appropriate sample with a lower percentage of fine particles. This was achieved by extracting the sample at the stage in the production cycle before the final sieve. It is worthy to notice, that this material was the major component of the oldest hand-mixtures used for building construction purposes in Palestine till the introduction of the concrete technology in the first half of the twentieth century.

-          Hydrated lime, available on the local market in the form of 25kg bags, and still widely used in the restoration process and is prepared for use by soaking it in water for at least three days.

-          Hydraulic lime, available recently on the local market in the form of 25kg bags (NLH 3.5), and gradually is being used in the restoration process. 

-          White cement, available on the local market in the form of 50kg bags. Recently, this material is still added rather in various amounts to make the mixtures dry faster.

Porosity Test of the Stones

The laboratory tests started with the assessment of the density (dry & bulk) and the optimum absorption ratio of the stone samples extracted from different sites in the Old City of Jerusalem (Table 1), as well as for stone samples from several quarries that provided in the past and still provide stones for the restoration activity in the city (Table 2).  These quarries are at A’nata, a village near Jerusalem famous for its ka’kooli limestone (medium soft stone), at Birzeit, and at the various locations in Hebron, Bethlehem, Beit Fajjar and  the Jordan Valley, which stones were used and are used extensively at the present time by most of the local institutions working on rehabilitation of Jerusalem structures. All samples were cut on a stone-cutting saw and fashioned into cubes of uniform dimensions in order to simplify the testing procedure. Porosity was measured through the void spaces in each sample, and is presented as a fraction of the volume of voids over the total volume:

n= (Vv/VT) *100=VT-Vs /VT) 100

Where Vv is the volume of voids, VT is the total volume and Vs is the volume of the solid parts.

The results obtained from the stone porosity tests, shown in Tables (1 & 2), reveal that the water absorption ratio for the stone samples from the Old City varies between 3.99% and 10.38%. These ratios are significantly higher than the measurements for the newly-quarried stones from Birzeit (0.74%- 1.05%), Hebron (0.74-1.07%), Bethlehem (0.98- 1.09), Beit Fajjar (1.75-1.86%), and the Jordan Valley (0.79%), which, as mentioned, are extensively used in the current restorations in the Old City of Jerusalem.  By contrast, the A’nata quarried samples show a ratio of (14.91-16.74%), which is higher than this ratio for the existing stones in the Jerusalem old structures. As for the density, the results in Tables (1 & 2) also disclose that this density for the stone samples from the Old City varies between 1.81 and 2.33g/cm³. All these density values shown in Table (2) are lower than the measurements for the newly-quarried stones from Birzeit (2.66- 2.69 g/cm³⁾, Hebron (2.63-2.70 g/cm³), Bethlehem (2.70- 2.72 g/cm³), Beit Fajjar (2.57-2.59 g/cm³), and the Jordan Valley (1.97 g/cm³), while the A’nata quarried samples show a density of (2.00-2.03g/cm³), which is compatible with the average density of the existing stones in the Jerusalem old structures (2.08 g/cm³).

Comparing all these ratios with the results in Tables (7 to 9) will show that it is possible to determine the porosity of the stones in an old building being subjected to restoration, for the purpose of defining both the appropriate stone material- in terms of absorption ratio and density- to be used in replacement of deteriorating stones, and for defining the location from which to obtain the stone to be crushed and used in the preparation of the hand-made mixture, suitable for each case of restoration, considering that the  deteriorative effects differ from one place to another, from one building to another, and even from one facade of a single building to another, according to the stone’s origin and its ability to resist against the different deteriorative factors.

....to be continue....

STONE RESTORATION part 2

STONE RESTORATION PRACTICE IN PALESTINIAN TERRITORIES:

A CASE STUDY FROM JERUSALEM

part 2

DETERIORATIVE FACTORS OF STONES IN JERUSALEM

“Jerusalem stone” is an exceptional name known worldwide and is rated very high for its unique qualities, including both strength and durability ^[6]. The various techniques of local stone finishing reveal an intimate knowledge of the material, acquired by generations of stonemasons. The stone finishes range from rock-faced (with or without tooled margin) to pointed, crandalled and brush-hammered styles. The types of masonry, i.e. stone size and shape, also vary with the importance of the work, from polygonal dry-rubble masonry to finely cut ashlar work ^[7]. However, within a particular building, or even a neighborhood, the basic type of masonry construction will usually not change in style or in the quality of materials. It can differ, however, in its external surface finishing and in its jointing. The color of the local masonry follows the limited palette of nature, ranging from yellowish stone, with hues of red and brown, to all possible shades of gray limestone available in the Jerusalem region.

Most of the residential structures in Jerusalem’s Old City were built in Ottoman times (1516-1917), but there are still extant some important buildings dating back to the earlier Mamluk and Ayyubid eras ^[8]. The limestone used in most of these buildings was obtained from quarries situated next to villages located around Jerusalem, places such as Beit Hanina, Deir Yassin, A’nata and Hizma. The laboratory tests conducted at Birzeit University on stone samples from the area of Jerusalem show that this stone is a rock limestone ingredient that has an average compressive strength of 15.8 Mpa, an average density of about 2.08g/cm³ and an average absorption ratio around 7%. (Tables 1 & 2 provide more details about the density and absorption ratio of stones selected from different buildings inside the Old City of Jerusalem and from A’nata, the Jordan Valley, Birzeit, Bethlehem and Hebron areas).

The earlier restoration activities in the Palestinian territories concentrated on renovation of the plastering and/or the pointing between stones, doing necessary fillings where needed and replacing missing or corroded stones in the building façades. This process took no regard of the physical, chemical and mechanical nature of the existing stone material, and because of this the results were often very modest and impermanent. The past and present treatments of deteriorated sections of stonework involve two basic steps:

-          Extraction of the damaged parts, either totally or in part, and replacing them with other parts having similar dimensions, texture and color but without perceiving their geological characteristics. This manner of treatment depends, at its best, on the craftsman’s accumulated experience and his knowledge in classifying stones. At worst, it follows a random selection of materials, without paying attention to the stones’ origin and to what extent they correspond with the existing ones.

-          The use of handmade mixtures (mortars, fillings, sealants, etc.), all prepared without sufficient knowledge or definition of the specific qualities either for the existing stones under restoration or the new stones to be used in this restoration.

According to Khamaisi ^[9], 29.5% of the residential buildings in the Old City are currently in need of rehabilitation, and 11.4% of the residents require spatial expansion. Indeed, he explains that just 18.1% of current residential structures are actually suitable for living, which means that about 80% of all Old City residences require major rehabilitation, urgent maintenance or total revitalization! Unfortunately, the same general state of disrepair exists among public and religious buildings.

Our observations were conducted on selected public buildings with different functions situated within the Old City of Jerusalem: the Al-Ashrafeyyah School (Mamluk period), the Armenian Museum (Ottoman Period), the Spafford Children’s Center (mixed Ottoman and British Mandate periods), and Bab al-Silsila (Mamluk period). The observations of the stones visible on the exteriors of these structures show that these four buildings suffer from several causes of weathering and decay of stone masonry, the chief ones being salt crystallization, fracturing, crust and incrustation. Several different studies: Honeyborne ^[10], Zagari ^[11], Camuffo et al. ^[12], Camuffo et al. ^[13], Bonazza et al. ^[14], Rothert et al. ^[15], Smith et al. ^[16] explain that each of these phenomena has a recognizably different effect on the stone material. Some lead to a loss of substance of the stone while others lead to a disfigurement or disruption of the stone masonry, but not necessarily accompanied by any loss of substance.  The site visits and observations in the Old City of Jerusalem discovered evidence of the following causes mentioned, as follows:

Salt Crystallization: This was observed in all four of the buildings inspected. They all are exposed to humidity, which leaks through the stone walls due to the phenomenon of capillarity. The key factor is the differential composition (when considered in cross-section) of the traditional walls in the city: a rubble core between two layers of stone forming the wall faces, internal and external. Consequently, the salty crystals appear on the outer surface of the stone wall, forming a crystallized mineral layer. This is the crucial process creating damage to the main external surfaces of the buildings in the Old City of Jerusalem (Fig 2).   Fracturing: This damage appears in two of the buildings, due to repeated natural or man-made destructions and continuous population growth, i.e. the increasing pressure of ever more residents and the “life load” they are producing. In addition, improper construction techniques, specifically the thickness of the mortar filling and the laying of the building stones without regard to each stone’s geological composition (i.e. its pattern of stratified layers) has aggravated this kind of damage (Fig 3).

Crust and incrustation: appears in three of the buildings, apparently due to the absence of laws forbidding or at least limiting the movement of vehicles within the Old City, in view of the polluting emissions they spew forth. In addition, certain establishments such as bakeries serve to escalate such damage. All of this is in addition to the other environmental impacts on stone typical to a large city like Jerusalem (Fig 4).

It is already possible to conclude here that, among all the factors explored above, there is one common denominator: the crucial impact of humidity on the present status of the stones of Old Jerusalem. Therefore, the laboratory experiments in this study have concentrated on conducting an analysis of porosity, expressed as density and as water absorption ratio, for three groups of materials: stone samples taken from existing stones in use in the Old City; stone samples taken from the quarries supplying most of the stones used in the present restoration activities in Jerusalem; and finally materials mixed from various substances and used for restoration purposes in this city.

STONE RESTORATION part 1

STONE RESTORATION PRACTICE IN PALESTINIAN TERRITORIES:

A CASE STUDY FROM JERUSALEM

part 1

 Shadi Sami Ghadban*

 sghadban@birzeit.edu

Marwan  Ashhab,

marashhab@hotmail.com

Dr. Shadi Ghadban is a teaching staff member at the Department of Architectural Engineering/ Faculty of Engineering at Birzeit University, Palestinian Territories. His academic and research activities are oriented towards the problems of local traditional architecture and has several publications on this field. In addition, he has a wide experience, as consultant and project manager for a good number of rehabilitation and restoration projects in several major Palestinian cities, including Bethlehem and Hebron.

Eng. Marwan Al- Ashhab, is a civil engineer and holding a Master degree in the field of “Restoration and Rehabilitation of Buildings” from the Higher Institute of Islamic Archaeology, Jerusalem University. Since 1998 he established his own consulting office and started his activity as contractor for rehabilitation and restoration of old buildings in the city of Jerusalem. He is a research fellow at the Department of Architectural Engineering at Birzeit University.

ABSTRACT

The aim of this research is to study the present practice applied to restoring and improving the status of the stonework in the historic buildings in Palestine, concentrating on this practice within the boundaries of the Old City of Jerusalem, Palestine. This requires identifying the stones’ current conditions and the causes behind their deterioration, and defining the appropriate criteria to be monitored in dealing with the effects of ongoing deteriorative factors on the maintenance and rehabilitation of these stones, concentrating on the phenomenon of porosity.

The methodology implemented in this research is based on both tangible and intangible components. These include a survey of the literature, direct observations through site visits, the photographing of certain cases, and collecting and analyzing samples from the various sites as well as from among the building materials available on the local market. All the samples were subjected to laboratory testing at Birzeit University in order to determine the properties of the materials to be used in the restoration process.

The research concludes with the drafting of specific recommendations and suggestions to be used in the field of stone restoration practice.

Keywords: Stone properties, Deteriorative Effect, Laboratory Testing, Historic Buildings, and Authenticity.

Postal Address: Department of Architectural Engineering

Faculty of Engineering- Birzeit University

Birzeit- P.O.Box (14)

Palestine

Tel: +972 2 2982119

Fax: +972 2 2982984

Running Head: STONE RESTORATION: A CASE STUDY FROM JERUSALEM

INTRODUCTION

Architecture in Palestine has been a product of the larger cultural development along the eastern shore of the Mediterranean basin, and has been influenced by historical events that repeatedly caused great dislocation and mixing of ethnic groups. One result has been diverse populations – having different governing systems, customs and other cultural traditions –living very close together. In this way, the necessary conditions were established for mutual influence to take place, during the process of the formation, development and enrichment of inventive traditions and values ^[1].

The historical cities of Palestine were thus formed and shaped as a result of this remarkable dislocation and juxtaposition of ethnic groups. They have undergone in the past, and are still increasingly exposed to, a long process of development beginning (in the case of the city of Jericho) some 10,000 years ago. The material traces of these cities reflect long centuries of human history condensed in a limited area, presenting to us the living image of the local historical and cultural environment over time (Fig 1).

Stone is considered the main building material in these cities due to its abundance; its splendid display of color ranging from white, to yellow, pink and gold; its inherent strength to resist different weather conditions; and its particular geological characteristics. This reliance on stone construction is reflected in a substantial range of historic buildings, structures possessing high cultural heritage value and authentically reflecting the various civilizations that prevailed in this region.

In the case of Jerusalem, the city not only has experienced some 5,000 years of human development, but it still occupies a special place in the world, especially as the focus of three  great religions: Judaism, Christianity and Islam ^[2]. Throughout its historical development spanning many centuries, this city has accumulated many occupational layers, and was subjected at least eighteen times to significant damage from natural or manmade sources of destruction ^[3]. The Old City in particular has been substantially rebuilt several times, reaching its current configuration in the  period of Ottoman rule ^[4].

The city witnessed periods of major restoration during the Eighteenth, Nineteenth and Twentieth Centuries, focused mainly on the early Islamic and other religious monuments in Jerusalem. This trend was one part of a larger program implemented by the Ottomans in order to control the region, and also the result of competition among various religious groups and foreign powers for primacy in the city ^[5].

Beginning with the British Mandate over Palestine in 1920, continuing during the  period of Jordanian rule (1948-1967), and finally under the Israeli occupation (1967-present), the restoration process proceeded slowly, and now a trend is evident toward growing awareness of issues concerning the rehabilitation or restoration of major religious or public buildings and compounds in the Old City. The present initiatives are largely funded by non-governmental organizations, employing guidelines and techniques reflecting the European experience in the field of restoration, and technical standards and charts  approved by international organizations such as UNESCO, ICOMOS, ICCROM, REHABIMED, etc. At this stage, the stone restorations have continued according to previous established practices, mainly those related to replacing of damaged or missing stones, plastering and pointing and treatment of any detectable deterioration in the stones of the historical buildings. Thus far, however, this practice has not considered the physical characteristics of the stone material itself, especially its ability to withstand various deteriorative factors.

In 1993, the Palestinian Authority was established according the provisions of the Oslo Interim Agreement. As a result, since about 1998 several large-scale restoration and rehabilitation projects, both international and local initiatives, have been undertaken, giving rise to a new Palestinian awareness towards the restoration and rehabilitation of buildings (one of its main objectives being to counteract the Israeli campaign of “Judaizing” the Old City of Jerusalem). Thus, various organizations, local and international, started restoring and/or rehabilitating different public and residential structures. This work has proceeded sporadically and at a low level, continuing with the same techniques as used in the previous periods. Specifically, all the operations were carried out without any sort of laboratory testing, analysis that would obviously help in defining the quality of both the old, existing materials employed in the buildings and the new materials to be used in any restorations.

Thus, the main objective of this study is to examine the present practices used in the restoration of stonework within the historic and traditional buildings in Palestine, through a case study from Jerusalem, concentrating on how to help upgrade the prevailing practice through the proper, informed selection of materials, according to standardized, measurable criteria, all the while preserving the materials’ authenticity as to their color and shape, and insuring the 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 identifying the current condition of these stones, the causes behind their deterioration, and defining the appropriate criteria, within the practices prevailing in the country, for managing better maintenance and restoration process.

To achieve this objective, a methodology based on both tangible and intangible components shall be presented and implemented in this paper. It includes a survey of the existing literature, field observations through site visits, the photographing of certain cases of deterioration, and collecting and analyzing samples from various existing structures as well from the building materials available on the local market and commonly used in restoration operations. All of the collected samples were subjected to laboratory testing at Birzeit University laboratories in order to examine their nature and properties. Of special interest were those properties of the materials which, in the context of a rehabilitation process, influence long-term durability, i.e. factors which will support preserving the authenticity of the stone structures while also insuring their maximum stability against various deteriorative changes. These findings will help in the selection of the proper stones for restoration of each case separately, and will guide the preparation of the necessary mixtures (mortars, fillers, etc.) which can be custom-made for specific applications and will thus be suitable for the most effective restoration actions in a wide range of future projects.

.....to be continued....