The Aspect of Color Optimization of the Mineral Repair Mixture for the Brickwork Restoration

The paper presents the testing of the optimization method of the composition of repair compound to a historic brick to compensate its losses, consisting in a step-by-step selection of mineral raw materials which ensure color identity and affinity of structures. Ceramic filled bricks of 1859 and 1786 were used as samples. Their color characteristics in the CIE L*a*b* system are studied. It was found that the cement-sand repair compositions prepared at the first stage of the study with the addition of modern bricks in the form of crumbs and powder do not correspond in their color characteristics to historical bricks. To eliminate the color difference, in the second stage various experimental techniques were used to increase the values of chromatic components a* and b* (increasing the fineness of fillers grinding, removing cement milk from the surface of samples of repair compositions), and various pigments were introduced into the repair mixture. As a result of this adjustment, it was possible to obtain repair mix compositions that correspond to the ranges of historical bricks in all three color characteristics.