Color changes in the surface of granitic materials by consolidated and/or water repellent treatments

Abstract

Color is one of the parameters to be monitored when determining the suitability of a protective or conservative treatment of stone. Application of a given treatment product should elicit the least possible effect in this parameter. Changes in color of five varieties of granite of highly varying characteristics due to their origin are studied in the present work. All the granites studied are widely used in buildings of historical interest in Avila (Spain). Some varieties are from unaltered facies (grey granites of different grain size), and have a very low degree of porosity, while other are from facies that have undergone strong natural weathering processes, and that display important mineralogical and physical changes. In this sense, the ochre variety of granite contains clays (smectite and some kaolinite); the white variety contains kaolinite and opal, and the red variety contains kaolinite, opal, and iron oxihydroxides. Fresh cut and artificially aged (with 25 cycles of freezing/thawing and cold/heat treatment) samples were treated with consolidant (RC80 or RC70) and/or water repellent (H224) agents. After the corresponding statistical treatment of data obtained, significant changes in ΔE were observed with the treatments given; such changes are more pronounced in unaged samples. Changes in ΔL (lightness), however, despite being noticeable, seem to have only a minor effect on ΔE, which seem to be more dependent on changes in Δa and Δb. This was more pronounced when the stone was treated with RC80 and then with H224. © 1997 John Wiley & Sons, Inc. Cal Res Appl, 22, 133–141, 1997