Earthen and hydraulic mortars used at Lavrion during classical antiquity (5th – 4th century BC) – A fundamental relationship between earthen building tradition and sophisticated hydraulic binders and concrete

In Lavrion, silver-bearing ores of lead have been processed to produce silver since prehistoric times. During the fifth and the fourth century BC, an intense exploitation of these ores took place, correlated with a certain historical context of a decisive culmination of wealth and political power of the Athenian Polis (city state). As a result, built structures associated with ore-processing are still ubiquitous at a huge scale in the area. This paper focuses on the mortars, both hydraulic and earthen, used in these structures. At first, a commonly shared building pattern is acknowledged and explained. Earthen mortars were used as structural mortars of stone masonry, while hydraulic mortars were used only as renders. The study on earthen mortars revealed properties similar to those suggested in modern earth-building handbooks and standards. In addition, the production of earth mortars with discretely varying characteristics according to their use, is a noteworthy find. The hydraulic mortars were applied on structures in contact with water or where industrial activity took place. The system of plastering comprised of two distinct materials, both hydraulic: 1) The thin waterproofing layer and 2) the substrate mortar, for which our ongoing research, combined with results of past studies, reveals that it is a hydraulic concrete with extraordinary properties such as high compressive strength, high density and low porosity.