Fascinating article about the extensive facade restoration work on the Smith Campus Center at Harvard University. From hand-sounding the concrete to testing 37 different cleaning methods to dozens of trials to match the existing concrete, a lot of painstaking care went into restoring this 60-year-old structure. We applaud this restoration team!

Concrete Construction details the restoration and color-matching:

Even when clean, 60-year-old concrete does not look like it did when it was new. Carbonation slowly shifts its tonality from gray to tan, and the thin, brittle, cementitious laitance wears away to expose more particles of aggregate, further changing both texture and hue. Casting against smooth formwork surfaces creates textures that differ from troweled applications, making it difficult to replicate the original attributes of historic concrete façades, even with skilled workmanship and detailed specifications. It doesn’t help that most concrete facades have many changes in texture due to variations in placement where aggregates and paste settle differently within and against their original formwork—not to mention fifty years of exposure.