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How were walls prepared before wall mosaics were installed?
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mosaic
Mosaic floor fragment from a synagogue or church, cut stone with mortar from Israel, late 5th–6th century ce; in the Jewish Museum, New York City.
The preparation of walls for mosaic installation was a meticulous process designed to ensure stability and durability. The procedure typically involved the following steps:
- Waterproofing: In many instances, the wall surface was first treated with a layer of resin or tar to provide waterproofing.1
- Mortar Layers: Two layers of coarse, roughened mortar were applied to the wall. To enhance the stability of these layers, large nails were often driven into the wall's joints before the work began.1
- Final Layer: A third, final layer of fine-consistency mortar was applied. This layer frequently included binding elements such as pounded brick and powdered marble.1
- Underpainting: Artists often created sketches directly on the setting bed or even on the underlying brick wall to serve as a guide for the placement of the tesserae.1
Similar to fresco painting, the setting bed was applied in small, manageable patches to ensure the mortar remained workable throughout the day's progress.1