Experimental Understanding of the Technology of Sgraffito Decorated Renders

Sgraffito technique was used to decorate renders by scratching the top layer of lime coat in the Renaissance time. This technique required both artistic and craft skills and its quality and durability relied on the selected materials. This type of decoration typically consists of geometric ornamental patterns symbolizing masonry blocks and other architectural tectonic features as well as figural depictions of various religious and profane motives. The main conservation issues currently relate to delamination of the render layers from the substrates, surface weathering and loss of drawn details, and incompatible and insensitive previous repairs. All sgraffito facades that have been exposed are nowadays either deteriorated or restored. Sgraffiti preserved in their authentic form exist only when covered by later render layers or sheltered by adaptations. An experimental approach was employed to improve understanding of the original Renaissance sgraffito technique based on the creation of a technological replica of an authentic sgraffito from Slavonice. It aimed to guide the repair mortar formula and its application. It has shown that the raw materials used influenced the engraving method, troweling and shading, line thickness, color and texture. Practical trials brought important findings on the technique including verification of the shading method. The study of the technological aspects complements the compatibility and performance requirements of the repair materials.