The Characteristics and Properties of Rubbing Bricks used for Gauged Brickwork – Part Two SARA PAVÍA AND GERARD LYNCH

This paper provides a continuation of ‘The Characteristics and Properties of Rubbing Bricks used for Gauged Brickwork – Part One’, published by Gerard Lynch and Sara Pavía in the March 2003 issue of the Journal of Architectural Conservation. In this, the authors examined the historical background, raw materials, production methods, use, and weathering characteristics of rubbing bricks. Despite the softness and absence of a protective fireskin, ‘low-fired’ rubbing bricks are extremely durable. This paper determines the properties and mineralogical composition of these bricks in order to understand their behaviour in response to weathering. It is concluded that the hardness and durability of rubbing bricks are due partially to the occurrence of mineral cements created by reactive temper. This temper acts in a manner similar to a pozzolan in a hydraulic lime mortar, giving rise to the development of mineral cements through hydraulic reaction. The rubbing bricks show a high level of effective porosity, which influences the production of mineral cements and the overall durability of the bricks.