Back in the mid-1990s a grinding and polishing equipment manufacturer invited me to teach a class on design techniques and chemical staining while a new process called diamond polished concrete also was being taught. Although many students were very receptive to the interesting effects of chemical staining, the focus was on one big machine slowly advancing across the floor leaving behind a stunningly smooth surface that you could actually see your reflection in. It was during this class that we unsuccessfully tried to combine both techniques--staining and polishing. Some of the stain did react and penetrate; however; most of the color was simply abraded away during the process. On my drive home I began to think about a better way to combine color with the polishing process, but the bigger picture was the huge potential this process had. These floors could offer light reflectivity, reduced annual maintenance costs, longer service life, less dusting, and aesthetic value. Several months later, one student asked, "Where is the decorative industry headed? What will be the latest and greatest?" My answer--colored, polished concrete.
ORIGINS OF POLISHED CONCRETE
To fully understand the process of polishing concrete I had to know its true derivation: the terrazzo industry. Terrazzo, meaning terraces, dates back to the 15th century. Venetian workers would embed small marble chips, remnants of larger marble slabs, in a clay-like anchoring system. This rather crude installation left behind an irregular surface. Their polishing equipment consisted of rubbing stones that they used while on their hands and knees to smooth and level the surface. After years of intense labor, and maybe a project manager demanding increased productivity, they developed a tool called a galera. It was a rubbing stone attached to a long, weighted handle. Now workers could put their weight behind it and abrade the surface faster, producing a smoother surface and increasing production. The problem, though, was that much of the natural color of the marble chips was lost because of scratches and dust. While cleaning this dust, they realized how beautiful the surface was when wet. This wet surface, ironically, is very similar to a newly sealed acid stained floor. Later Venetian workers discovered that when they sealed the floor with goat's milk, the beautiful colors of the aggregates would reappear and remain when dry.
In the United States, in the mid to late 1920s the same rubbing stone concept took a monumental leap when workers attached similar rubbing stones to electrically operated machines. This launched today's terrazzo industry. Despite many technological advances in the equipment, the same logic applies to modern grinding equipment. But terrazzo grinding machines now use diamond bits or pads to abrade, level, and smooth the surface.