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Polishing Concrete

Imagine a concrete floor as shiny as glass. This is a look that diamond polishing can achieve. Two years ago very few people in the United States had even heard of polished concrete other than terrazzo floors. Terrazzo floors use carborundum stones to grind and polish floors to a 120- to 150-grit finish (grit refers to the micron particle size of the diamonds or other grinding abrasive materials). Diamond-polishing technology now makes it possible to grind and polish much faster on concrete surfaces at up to 3000-grit finishes.

Today, most decorative concrete contractors are aware of the creative possibilities that polishing techniques can add to their finishes. But the reasons for polishing concrete go far beyond decorative. Warehouse owners, for example, are willing to pay for diamond polishing of their floors in order to reduce maintenance costs and solve problems involving sealers or water vapor transmission. A National Sales Manager for Vic International, Knoxville, Tenn., notes that an added benefit for warehouse applications is that forklift tire marks don’t adhere to the surface.
But the new technology for polishing concrete comes from the stone-polishing industry, not the terrazzo industry. It has been available for 4 years in the United States with significant improvements in the past year-especially in dry, dust-free grinding. Although there have been polished concrete floors in Europe for about 8 years, advertised as “superfloors,” developments in diamond technology are the result of U.S. efforts.

If Concrete is placed and finished so that the surface of the floor is very flat, polishing can be achieved entierly in the cement-paste/fine-aggregate layer. As seen above, a 3000 grit finish provides a highly reflective finish.

Advantages of Polishing

Saving money on maintenance, solving existing concrete problems, providing commercial floors that don’t show traffic wear (store aisles, for example), and providing new, artistic decorative concrete surfaces are the most common advantages of polished concrete. Polished concrete floors are essentially no-maintenance surfaces. Owners of commercial and warehouse floors typically find it expensive to maintain their floors with sealers and waxes. And if a floor surface is sealed so that water vapor can’t get through, then polishing the floor can be a one-time fix that saves money. After diamond polishing, the only maintenance required is removing dirt, oils, and other materials that could stain. Even chewing gum won’t stick to a polished floor, according to a president of a company that specializes in warehouse flooring and large commercial projects.

Diamond polished floors also have good water vapor transmission. Some advances in the industry has come from others failures, for example removing epoxy sealers that have caused trapped water problems or that haven’t bonded properly.

When you know ahead of time that you will be using "Exposed Aggregate" concrete polishing techniques for artistic appeal, you can add "Decorative Aggregates" to the concrete that will appear to be brought to the surface when the polishing is performed.
Seen above is polished concrete using decorative aggregates such as metal, slabs of stone, and other materials.
This technique can also be used for "Counter Tops" perhaps in place of Ganite or other natural stone counter tops.

How the process of concrete polishing works

The first step in polishing concrete is to remove any existing sealers and coatings by shotblasting or with coarse diamond cutting heads. Next, any defects are patched. Cracks, control joints, and isolation joints are filled with flexible epoxies so that the grinding bits can easily pass over them.
The two types of diamond grinding heads used for polishing floors include diamonds embedded in a mortal matrix (right) for coarse polishing and in a resing matrix (left) for fine polishing.

A sales and technical representative, recommends using 25- or 30-grit diamond cutting heads to remove concrete faster if an owner wants to reveal the aggregate in the concrete. Another expert recommends starting with 40-grit diamond cutting heads if polishing is to be confined to the surface layer of cement paste and fine aggregate.

The purpose for this first grind is to remove the lumps and bumps left by the finishing process and also to remove the curling that typically is found at control joints. Most of the removal occurs in this first step.

Soft concrete consumes more diamond that does hard concrete and hard concrete typically produces a better polish. It is best to perform all coarse grinding steps first and chemically harden the concrete before polishing begins. We recommend two applications of a chemical hardener such as sodium silicate after the first grind.

Lithium silicate or fluorosilicate products will also work. These products react with calcium hydroxide in the concrete to produce additional cemenititious material. The process closes some of the pores in the concrete, adding stain resistance. The entire process removes approximately 1/16 inch of concrete.

Adapted from the stone polishing industry, machines used for polishing concrete floors are referred to as "Planetary Head Grinders". One Large head travels in one direction while 3 satellite heads mounted on the large head rotate in the opposite direction. Diamond blocks are attached to the satellite heads. This arrangement causes the grinding heads to travel somewhat randomly over a large area.

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