The conservation work in Wilson’s Arch was conducted simultaneously with the restoration and development of the site that included the construction of a new women’s gallery (ezrat nashim), infrastructure replacement, replacement of pavement, and the installation of an air conditioning system. This work was intended to improve the appearance of the covered area adjacent to the Western Wall plaza and provide convenient access to the prayer halls.
The work was carried out in stages, some during the night out of consideration for the worshippers. The areas were also partially closed off at the time work was being conducted there.
Examination of the state of preservation
(1) Examining the Wilson Arch complex: the Mabat Company performed a laser scan of the structure in order to check the engineering stability of the vault. The surface of the vault was scanned and a virtual three-dimensional model of it was built. This model was measured against a geometric model in the shape of a half-cone to test for engineering distortions. During the measurement the northern side of the vault was found to be approximately 10 cm lower than its southern side; however, no settling or distortion was found indicating damage to its stability. Leakage in the area of the vault and salt crystallization and incrustations on the surface of the vault stones were also documented. No exceptional fissures or gaps were found in the joints between the masonry stones.
(2) Examining the physical state of the vault stones: a physical survey was conducted during which every one of the masonry stones was documented and the different problems were located and marked on a drawing of the vault. The main problems are: cracking, voids in the stone, salt crystallization and incrustation, and the disintegration of the stone. The factors responsible for producing the voids inside the vaults stones are: 1) the original construction manner whereby the stones were set in place opposite the direction of their layered deposition; 2) the flow of the upper run-off from the direction of the Chain Gate and; 3) the flow of waste water from the direction of the “Machkema” building.
An acoustic examination performed by means of gently tapping on the surface of the stone with a rubber hammer revealed internal voids inside the masonry stones.
(3) Examining the condition of the stone: salinity tests were performed on the stone to determine if it has undergone any changes in its chemical composition. The salinity test revealed that the amount of salt in the stones is one hundred times greater than normal. Changes in the water content in the stone have resulted in destructive action by the salt and structural changes to the stone (collapsing and disintegration) to the point that in certain instances the original strength of the stone has been diminished. Nevertheless, the excessive moisture inside the stone has prevented the salt from crystallizing and in most cases, therefore, the stones have not lost their original shape; however they have been weakened.
The absence of massive buildings above the vault has saved it from being subjected to concentrated vertical pressure.
An analysis of the three aforementioned aspects demonstrates that from an engineering standpoint the vault is stabile.
Subterranean cavities that were constructed as foundations for the public buildings that were erected in the Crusader and Mamluk periods are supported up against Wilson’s Arch. Over the years these cavities have been used for, among other things, water cisterns and as gathering places. Many of the problems that have been treated in these cavities stem from modern intervention that is incompatible with the original construction materials.
Plaster. Some of the vaults in the complex were covered with layers of cement-based plaster. This has caused damage to the original building materials due to the accumulation of sodium salts, a weakening of the original lime-based bonding material and damage to the surface of the stone.
Stabilization. A “thickening” was built onto the northeastern side of the vault, probably in order to stabilize it. The need to stabilize the vault most likely stemmed from the physical condition of the masonry stones. This “thickening” was built of remnants of modern masonry stones and has become a serious aesthetic eyesore.
Conservation measures. The conservation intervention at the site included the following measures:
Dismantling the plaster and the cement bonding materials.
Dismantling modern supports
Cleaning the original bonding material.
Affixing stone, inserting fiberglass rods (6 mm in diameter) and filling the cracks with lime-based bonding material.
Re-attaching and returning masonry stones to their original places.Filling voids inside walls/pillars (grouting).
Pointing up joints.
Removing soil fill.
Building supports by means of stone rubble construction in order to highlight the fact that it is new and not original construction.
Inserting steel anchors.
Inserting threaded rods.
A detailed report of the work in the compound is on file in the conservation archives of the Israel Antiquities Authority.
The conservation team wishes to thank the Western Wall Heritage Foundation for the opportunity it provided to take part in the development of this important site.