| The Old City of Akko (Acre) |
| The Hospitaller Center |
| Crusader plaster on the southern road, 2003 |
| Orderer | Old Akko Development Company, Ltd. |
| Duration | 2003 |
| Address | Block: 18009, Lot: 2 |
| Implemented by: |
Yotam Carmel
Orit Soffer
Avner Hillman
|
The southern road is the street that runs south of the Hospitaller fortress, along the Crusader level. The aim of the project was to conserve the remains of the Crusader plaster there.
The southern road is below ground where the prevailing climatic conditions are problematic. They are characterized by high humidity, high temperatures in the summer and cold temperatures in the winter, a lack of ventilation and the exposure to artificial lighting for prolonged periods. All these are factors trigger various conservation problems. The high level of humidity together with improper lighting and the lack of ventilation provide ideal conditions for the development of biological nuisances as can be seen on large parts of the walls in this area. Extreme and sudden fluctuations in the level of the humidity or temperature are likely to cause the salt inside the wall to migrate resulting in the deterioration or detachment of parts of the plaster.
The stone walls of the road are covered with the remains of white plaster that is probably Crusader in origin. We are dealing with one or two layers of plaster, a total of c. 5 mm in thickness. The composition of the plaster is unknown but we can assume that it was prepared on a basis of pit lime and sand or powdered limestone. The plaster remains on the street’s northern wall have undergone basic conservation treatment that has included reinforcing the edges of the plaster. The plaster on the southern wall has not been treated at all and as a result its condition is considerably worse. We believe that part of it has separated and been lost since the walls were exposed.
A wooden walkway was built as part of the development work at the site. While conservation measures were being carried out incised marks were detected on the plaster. These depict various Crusader symbols such as boats, a shield etc. Some of the symbols are clearly visible; others are partially covered with patina or are partly preserved as a result of pieces of the plaster having detached from the wall.
Weathered plaster is characterized by the detachment of the plaster layer from the wall, the weakening and deterioration of the plaster (it crumbles from just the touch of a hand), a biological patina the result of climatic conditions that are favorable for the growth of microorganisms, a gray patina that probably consists of cement and salt, a layer of dust on the surface of the plaster, cracks and lacunae. The exposed earthen floor also causes a layer of dust to accumulate on the surface level.
The treatment of the Crusader plaster on the southern wall focused on measures that would stabilize and strengthen the plaster. Attempts were also made to remove the different patinas and detect other etchings in the plaster, but these were of no avail. These measures included an initial dry cleaning of the plaster surfaces with brushes, “WISHAB” sponges, and a scalpel; cleaning and exposing the edges of the plaster by means of water and a brush; stabilizing the edges with a pit lime based bonding material (the composition and color of the material were determined in accordance with the thickness and color of the original plaster); filling the spaces between the plaster and the wall by injecting a liquid hydraulic lime based bonding material. In order to avoid introducing excessive amounts of water into the wall, spaces were filled only in instances when the gap between the plaster and the wall extended across a relatively large area or when it was clearly apparent that the plaster was in imminent danger of separating from the wall.
We conducted several experiments to remove the patina from the surface of the plaster. We tried to remove the biological patina by means of Preventol compresses, in a 10% concentration for 30 minutes. The gray patina we attempted to remove using chemical (water, alcohol, ammonium carbonate) and mechanical means (scalpel) without success. The patina probably contains, among other things, cement and its resistance is greater than that of the plaster. An attempt to soften the patina by means of compresses was of no avail. The large amounts of water which the plaster absorbed from the compresses caused the immediate migration of salt and the uplifting of the plaster in the area where the attempt was performed. Consequently we decided it was best to avoid any further experiments.
The ambient conditions of the street necessitate more stringent maintenance, the installation of a system that records the level of humidity and temperature, and the installation of a suitable lighting system that will operate only during visits or when work is being conducted there.
To view the figures, click on the figure caption
|
