| Jerusalem |
| The Old City |
| A Plaster 'Pilot' Project in the Crusader Cardo |
| Orderer | The Jerusalem Development Authority |
| Implemented by: |
Avi Perets
Arch. Avi Mashiah
Arch. technician Yuval Avraham
Eng. Yaacov Schefer
|
The conservation project in the cardo compound, located in the Jewish Quarter, was initiated as a result of plaster chunks that broke apart risking the passersby there. The cardo is divided into three sections according to its structural features: the open cardo, the covered cardo and the Crusader cardo.
The last section – the Crusader cardo – is a vaulted street with a modern apartment building constructed above it. This section of the street, where the existing modern cement-based plaster was disintegrating, is very active both from the standpoint of commerce and tourism.
After conducting conservation and engineering surveys there and in order to remove the hazard of any further crumbling and falling plaster, it was decided to execute a ‘pilot’ project in the Crusader cardo section so as to evaluate the implications of (1) removing the existing plaster, (2) implementing stabilization and conservation measures, and (3) applying new plaster.
Among other things our examination revealed that water penetrated into the vaulted structure – probably from the apartments above, as well as from the adjacent streets – thereby conveying salts, which are one of the main factors behind the breakdown of the plaster.
Since this project could not prevent water from penetrating into the building we sought a solution in the form of a plaster product that is capable of withstanding the existing environmental conditions and which would not cause any damage to the ancient building materials.
One of our material venders suggested we check out a new product in the country which is manufactured by the Weber Company and based on the technical specifications appeared to fit our needs. In order to achieve optimum results the factory engineers where the product is manufactured provided training and demonstrated the proper use of the product. We decided to use the same factory’s products so as to ensure maximum suitability between the different materials that the treatment required.
The pilot project included dismantling the plaster, drilling test holes to identify cavities in the vault and mapping them. Next we cleaned the joints between the vault stones, washed them and filled them with Weber Calce mp. 2.5. In those places where there was a large gap between the vault stones we inserted stone wedges (klinim) to increase the surface friction between the stones. We inserted pipes into the core in order to inject mortar in the cavities in the vault. Having completed pointing up the joints and prior to injecting the mortar, we supported the different parts of the vault by means of wood to the floor of the scaffolding and at the same time toward the ground in order to prevent the scaffolding from collapsing. The supports were built in such a way as to allow pedestrians to pass beneath the scaffolding while the work was being done.
We used Weber Calce mp. 2.5 mortar in the stone courses that were dismantled and rebuilt. A layer of Weber Calce mp 2.5 mortar was applied so as to straighten the plaster in the vault. The vault was moistened in preparation the day before the first layer of EVOCAL plaster was applied. The plaster was applied one layer per day, without tamping, until the desired thickness was attained and then it was sanded. The finish layer was done using Weber Calce Finitura and we used Weber San Evoluzione plaster on a modern concrete wall.
The two kinds of plaster we used – lime-based Evocal plaster, and cement-based San Evoluzione – allow the water to evaporate from the wall cavity and remove the salts, without swelling or crumbling of the plaster. With regards to the application, both the amount of time required for air to enter the mixture and how the material is put on, without removing the air from it, are extremely important. This is unlike the usual method of plastering whereby the material is tamped down.
Today, a year after the completion of the pilot, we have discerned, as we anticipated, a larger amount of water penetrated into the vault in the winter; however, the crystallization of the salts occurs on the surface and does not cause the plaster to detach or crumble. The salt accumulation can be swept away and the plaster is not disintegrating. In order to achieve the desired results it was necessary that we carefully follow the manufacturer’s instructions for the preparation and application of the material.
Apart from the nature of the work in a bustling urban environment and having to deal with finding solutions to the physical problems and applying them, there were also other difficulties that arose with the implementation of this pilot project. For example, the merchants objected to us working during business hours and the residents objected to our working at night. There were safety problems that stemmed from the fact that it was not possible to close the shops and halt the movement of passersby who were mostly tourists, and of course there was the noise, the dust, and the like that accompany work of this sort. Further treatment of the cardo will be subject to a decision by the Jerusalem municipality and the allocation of the necessary resources to do so.
Avi Perets
-------------------------
May 2013
-------------------------
To view the figures, click on the figure caption
|
|
