Influence of limestone sludge (generated during the washing process of limestone crushed aggregates) with high content of CaO in the form of calcite on the properties of brick body made from non-calcareous sludge (from the washing process of quartz sand) as a basic plastic brick clay was determined. Presence of calcite very distinctly influenced the firing process and properties of fired body. Limestone sludge decreases firing shrinkage, bulk density and coefficient of thermal conductivity of the brick body after the firing in the range of 850 – 950 °C. Higher modulus of rupture and water absorption is typical for fired bodies with limestone sludge addition. Most of these improvement are caused by the formation of anorthite only in the bodies based on the limestone sludge.