In 2002, a few contractors aggressively marketed the concept of diamond polished floors.
Prospective owners were told that diamond polished floors were maintenance free and even the rubber skid marks from fork lifts didn't stick to the concrete. Owners also could save money on lighting because of the reflective quality of the finished work. These floors were marketed as aesthetically pleasing, so contractors experimented with chemical stains to add color variation. But the primary market was warehouse flooring because owners were upset with the maintenance costs associated with epoxy and urethane sealed surfaces.
At the time, there were only a few contractors doing diamond polished floors.
In the August 2002 issue of Concrete Construction, I authored an article examining the tools and detailing the “how to” steps described by contractors as they learned and solved related problems trying to produce good looking work and make acceptable profits.
So after five years of growth, how has the industry changed in terms of tools, procedures and the market for polished concrete floors?
The general design of floor grinders hasn't changed much but there have been several refinements. The primary tool, planetary head grinders, was adapted originally from the stone polishing industry. It typically consists of three or four “satellite heads” 10 or 11 inches in diameter mounted on a large “planetary head” 30 to 32 inches in diameter. The planetary head spins in one direction and the satellite heads, which hold diamond bits, rotate in the opposite direction. In this way the diamond bits travel in a random pattern within the diameter of the planetary head.
Compared to a grinder with a single head, planetary grinders produce a much flatter floor surface with less operator skill required. Brad Padget, CEO, Concrete Polishing Technologies, Norris, Tenn., says that some floor grinders are powered with propane now but most use either 220-V three-phase or 480-V three-phase electricity. And for convenience most contractors bring their own generators to the jobsite to power them. He adds that the features you should look for in a machine include counter rotation, variable speed control, adequate weight (800 to 1000 pounds for a 30-inch machine), and adequate power. Contractors currently are moving in the direction of 480-V systems.
Poinsettia Byrd, a technical sales and marketing analyst for Vic International, Knoxville, Tenn., says that planetary grinders have to be heavier duty for concrete applications than those used for polishing stone because they have to remove more stock, coatings, and sealers. So manufacturers such as Vic also sell models for more severe applications.
Today, satellite heads come with both flexible and flat surfaces. Flexible heads enable diamond pads to follow the contour of the floor to some degree, polishing small depressions in a pass.
Grinder bearings are high maintenance points so HTC, Knoxville, Tenn., solved the problem by installing hubs similar to those used by the automotive industry to reduce wear. Another concern is when a polisher catches something on a floor, the jolt can break drive belts and damage the machine. Vic now adds a clutch to disengage the power when this happens.
Diamond polishers are set up to grind wet or dry and some are set up to do both. However, John Abraham-son, president of HTC America, points out that 90% of the work now is dry polishing. Contractors would need tanker trucks to haul the slurry away from a big box retail project and the regulations for disposal of the slurry have become very difficult. Powder, on the other hand, can be disposed of in landfills (some grinders even bag it as they collect it) and workers always have a clear view of their work.
Innovetach, Everett, Wash., and HTC have introduced diamond polishers with four satellite heads, making it possible to rotate two heads in one direction and the other two in the opposing direction; the satellites on three-head machines all rotate in the same direction. This reduces operator fatigue because the machine doesn't pull in a sideways direction. Abrahamson adds that they are working on the idea of remote control and ride-on machines based on four-head technology.
Another direction that diamond pad innovation is taking, according to Kyle Wiggins, Innovetach's sales and marketing director, is to reduce the number of steps in the polishing process by developing pads that can incorporate several steps into one pass.
Handling edge details
Grinding and polishing edges continues to be one of the more laborious parts of the business. Big floor polishers typically can polish to within 2 inches of a wall. The last 2 inches is work for handheld tools. There are a few walk-behind edge grinders on the market but Padgett says that it often comes down to workers on their knees using angle grinders or a variation of that tool. In order to avoid this costly step, some building owners paint a strip on the floor along the walls to mask the area.
Diamonds and matrixes
Diamonds are both manufactured and mined, with most diamond pads using manufactured ones. They are embedded in either metal or resin matrixes (sometimes also referred to as “bonds”) in different densities. Coarse grinding steps are completed with metal matrix diamond pads while the finer polishing steps are accomplished with resin matrix pads. Wiggins says that managing heat buildup is a big problem, especially for dry grinding. If a diamond pad overheats, diamonds tend to break off flat rather than jagged, leaving the pad “diamond glazed,” says Wiggins. And if the matrix gets soft due to heat it can bond grits from the concrete, which scratch the surface, causing additional problems.
For the past few years much attention has focused on developing matrix materials designed for use on concrete floors with different degrees of hardness. In the past contractors have used up expensive sets of diamond pads because the matrixes weren't right for the conditions. It is considered to be very important now to run tests on a floor before production work begins. Byrd notes that there are testing devices available to gauge concrete hardness but they aren't perfect and the results can be misleading. She advocates also grinding a sample area first with a 40-to 80-grit head to judge conditions.
The diamond-polished floors market
The market for diamond polished concrete includes warehouse floors, retail stores, residential projects, and small applications, such as concrete countertops. The same equipment also is being used to prepare garage floors to receive decorative epoxy and poly aspartic urea finishes. Abrahamson says that the retail big box stores is where the most significant growth has occurred because they want low-maintenance floors that are aesthetically pleasing with good light reflectivity to save on electrical costs.
Diamond polished floors are being marketed as “green” as well. The green in this case doesn't relate to the concrete itself but what is eliminated. The concrete is already there, so for little additional investment a finished appearance can be achieved. Other floor coverings, including sealers and coatings, are petroleum based and this can be saved for other purposes. Polished concrete doesn't have vapors from solvents and plasticizers that can go into the air for years afterward.
When diamond polishing is specified for newly constructed floors, there are things that concrete contractors can do to greatly facilitate the polishing process. Achieving flatness requirements of FF50 and greater is the most important factor. The polishing process flattens floors, so when they are flat to begin with, there is less grinding required and less waviness of light reflectivity. Also, owners want hard-troweled surfaces to increase abrasive wear resistance. They don't want polishing contractors to grind through the most compacted layer of the concrete. When floors have raised or depressed areas, polishing contractors have to grind the areas flat which can compromise the aesthetic appearance. It's also important to make construction joints flat. Excessive curling at control joints can cause problems for polishing contractors.
Byrd says that the ideal compressive strength for polishing is 4000 psi. Higher strengths can be very difficult to polish. Lower strengths have reduced wear resistance. However, if exposed aggregate polished finishes are desired, 3000 psi concrete makes aggressive cutting easier, adds Byrd.
Working with concrete floor contractors
Abrahamson reports that there is a new trend among retail big box stores. They want hard-troweled finishes and in some cases burned finishes for the added surface hardness. They don't want aggressive diamond polishing—just enough to get the desired light reflective reading of 45 or more on the gloss meter and the aesthetic appearance. As concrete contractors achieve flatter floors, diamond polishing machines are used less and floor maintenance machines with Twister Pads developed by HTC, are used to complete the final polishing steps and cleanup work. They also are used to maintain floors afterward.
Abrahamson says that the diameter of the bristles on these brushes are much less than the bristles for floor scrubbing machines. Diamonds are incorporated in each bristle to provide polishing while the floors are cleaned, so that over time, maintenance increases the polished effect. Several different grit sizes are available for these brushes.
The diamond polishing industry has learned that the maintenance program an owner adopts has a great effect on the appearance of polished concrete floors. When dirt isn't periodically removed, it abrades the surface with traffic wear, quickly reducing the polished appearance. Also using acid- or alkaline-based cleaners can erode the surface of a floor. The bristles on traditional floor scrubbing heads also can cause damage. So diamond polishing suppliers have created their own products to help maintain or increase the polish.
Decorative polished concrete
The market for decorative polished concrete has just exploded, according to Joe Smith who owns Marblelife, Media, Penn. As a company that specializes in high-precision stone floor work, they began getting calls to install demanding concrete floor projects of 25,000 square feet or less. And that led to adding color, first with chemical stains and now with dyes—which he thinks is the best way to color polished concrete. Decorative work is in high demand for architectural firms, art galleries, retail spaces, homes, and franchise businesses, such as Harley Davidson stores who are willing to pay for floors that reflect the image of their motorcycles on display. Smith says that one art gallery project in a very old building with old concrete produced an affect that could not be duplicated anywhere.
A growing industry
Work for the diamond polishing industry started with large industrial floor projects and then included smaller projects—the opposite way most industries develop. Diamond polishing is the least expensive when floors are installed properly and are flat. It looks the best on those floors as well. And in the new green age that we are entering, polished concrete reduces the need to add floor coverings to complete a project.
To what degree should a floor be polished? The answer seems to depend more on the client than the industry. Finishes range between 800 to 3000 grit. Some believe that 3000-grit finishes have better abrasion resistance and slip resistance. There isn't, as yet, an industry standard that defines what the limits are for diamond-polished finishes.
Training is key. If you are thinking of being involved in this business you should take advantage of the training seminars offered by the companies that manufacture and sell tools.