Interventions in the 1960s and 1970s
The conservation of the mosaics in the east corridor and eastern part of the south corridor began in 1965 and continued for about a decade. The work involved the piece-by-piece detachment and re-setting of the mosaics on a new substrate with the use of strong cement mortars. On the contrary, the mosaic floor of the apse of the Basilica, which survived in relatively good condition, was not detached but rather was conserved in situ using cement mortar. During the period that intervened between the conservation of the mosaics and the early 1990s, when they were covered with geotextile fabric and sand, no care was taken for further protective measures, since available funds were insufficient for their systematic conservation.
In 2011, within the framework of the project for the lighting and restoration-enhancement of the mosaic floors (east corridor, eastern part of the south corridor, Basilica apse) of the Palace of Galerius in Navarinou Square, Thessaloniki, the Ephorate proceeded to the restoration and conservation of these mosaics, a project carried out in accordance with the study approved by the competent bodies of the Ministry of Culture.
The state of preservation of the mosaics before the intervention
In antiquity, the mosaic in the east corridor covered an area of 335 square meters, of which 230 square meters have survived. Correspondingly, from the eastern part of the south corridor, 65 square meters (out of an area in antiquity of 100 square m.) have survived. The poor condition of the mosaics was caused by their long exposure to environmental conditions (1973-1994), the use of cement mortars during their re-setting, and the absence of regular systematic conservation.
The following types of damage were recorded:
• detachment of the tesserae from their substrate and loss of mortar from their joints
• mineral salt deposits on the tesserae
• disintegration of the cement used to restore the destroyed sections
• topical detachment of the layer in which the tesserae were set from the substrate (underlying layer of mortar)
• cracking of the modern cement substrate due to the absence of expansion-contraction joints (as concerns the east corridor).
Conservation work
Conservation work in the east corridor and eastern part of the south corridor was carried out between 2011 and 2013 and included:
• cleaning of the tesserae by mechanical means and texapon
• the laying of the detached tesserae with compatible mortar
• the detachment of the cement mortar between tesserae to a depth of 0.50-1.0 centimeters and the filling of the joints with new, compatible mortar
• detachment of the cement mortar which had been used to repair the destroyed parts of the mosaics down to the lowest layer of the modern substrate (rock fill) and the construction of a new layer of compatible mortar
• detachment of selected parts of the mosaic (45 pieces over a total area of 24 sq. m.) whose conservation could not be done in situ, followed by their conservation and re-setting with new, compatible mortar
• construction of expansion-contraction joints wherever possible.
The above interventions were done using a compatible mortar studied by the Aristotle University of Thessaloniki’s Laboratory of Building Materials, taking into consideration the composition of the mortar used in the 1970s intervention.
