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Gypsum is one of the main building materials on the archaeological site of Knossos and was used extensively for walls, floors, column and pillar bases, door jamb sockets, seats, stairs, etc. Its age and composition make it a particularly fragile material. Indeed, the stones of the walls and floors of the Palace of Knossos have suffered extensive damage due to mechanical, chemical and biological factors and human intervention, combined with the local microclimate and the structure of the stone itself.

The gypsum in particular is badly eroded, mainly in the uncovered areas, due to its solubility in water and the subsequent distortion of its mechanical properties. At the same time, previously unrestricted visitor access to all parts of the Palace, and the added load, chiefly due to Evans’s restoration, have caused mechanical fatigue, wear and warping of the gypsum slabs.

The serious problem of the rapid wear of sensitive gypsum and limestone was solved in collaboration with the Stone Conservation Centre. The aims of the laboratory study (examining the types of damage and associating them with erosion mechanisms, conservation methods) and the application of the results to the site were the preventive and/or interventional conservation of the material and the disclosure of the results to the scientific community.

The work involved the removal of the mortar of earlier interventions from around the stones; mechanical and chemical cleaning of the surface and cracks; consolidation and repair of fragments; mortar injection and sealing of interior and exterior cracks using the corresponding mortars. Finally, large detached fragments of masonry were attached using titanium rods.

Furthermore, to protect the sensitive gypsum elements, small or larger roofs were constructed where possible, such as the small metal roof covered with polycarbon sheeting protecting the staircase of the “South House” (phot. 1), or a temporary roof of similar construction for the uncovered “West Magazines” (phot. 2). Work was also carried out to reduce the load on gypsum pillars subject to mechanical stress due to the overlying structures of Evans’s reconstruction, for instance on the peristyle of the “Hall of the Double Axes” (phot. 3).

phot. 1

phot. 2

phot. 3

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