One of the first guidelines developed by the Concrete Polishing Association of America (CPAA), Stevensville, Md., was a collection of definitions outlining what constitutes a polished concrete surface and what doesn't. Previously, contractors could submit prices for concrete ground to a 200-grit finish while their competition bid the work to an 800-grit finish—both calling the work polished. Faced with this, owners became confused, understanding price more than value. But today there is industry-wide agreement about what constitutes polished concrete. The CPAA currently defines three types of finishes:
- True grind and polish. Under this classification, work starts with metal-bond diamond bits in the 40- to 80-grit range and proceeds to 150-grit. Then the honing stage begins with resin diamond pads, proceeding in stages to 800-grit, or even 3000-grit as a final polishing step. This system normally is applied to existing or even new concrete that may have some irregularities, trowel marks, or unevenness requiring correction.
- Resin-only polish. When concrete surfaces are reasonably flat, as is the case with higher floor flatness (FF) numbers or concrete countertops, polishing can be accomplished with resin-bonded diamond pads. Using these pads, polishing typically starts at 60- to 80-grit and proceeds to 800-grit or even higher.
- Topical polish. Instead of using a diamond grinding machine (which typically runs between 400 to 1300 rpm), a burnishing machine with minimum speeds of 2000 rpm is used with maintenance floor pads that have diamonds embedded in the fibers. Burnishers quickly increase the gloss numbers for a slab, especially when silicate or siliconate products are applied during the process to further increase gloss readings.
When owners and specifiers know the required type of finish for an application, contractors can bid prices that everyone understands.
Trends and technical advancements
Clif Rawlings, product manager and training coordinator for HTC, Knoxville, Tenn., says 90% of their customers grind dry rather than wet now, even though wet grinding is still faster. One reason is because dry powder is collected instantly with a vacuum while wet slurries are more troublesome to remove. Also, the EPA allows powdered concrete to be disposed in normal ways but treats wet concrete slurry as a hazardous waste requiring special handling.
There have been significant advancements in resin pad technology. The ideal resin material operates efficiently under higher temperatures and can hold diamonds in position until they are worn out. Rawlings says manufacturers are blending different types of resin together, as well as mixig metal and resin, to create hybrid pads that wear in relation to how fast the abrasive surfaces of the diamond wear down. In addition, diamond manufacturers are coating diamonds with metals such as titanium, tungsten, cobalt, copper, and chromium. By doing this, they achieve better bonds between diamonds and resin or metal matrixes.
High- and low-grade quality diamonds also are blended together to increase production rates. Low-graded diamonds work best on high-density, stronger concrete, while high-grade diamonds cut more efficiently on lower strength, more porous concrete.
Ed Michels, marketing development manager for 3M Co., St. Paul, says they are introducing new diamond pad products that can be used for floor refurbishing, intermediate fine grinding, and topical polishing. Contractors won't need weighted machines that go through the typical five- to seven-step process, but rather can use traditional floor cleaning machines. The diamonds in their new pads are incorporated into precise, "structured" composite shapes to increase efficiency.
In recent years, owners of big box buildings (large consumer-oriented stores) discovered that hard-troweled floors burnished with plastic trowel blads as a final step provided better wearing surfaces. In order to avoid removing any of the hardened surface, owners skipped the diamond grind and polish step that provided the glossy surface customers liked. The industry responded by embedding diamonds of different grit sizes into regular maintenance strip pads mounted on burnishing machines, which resemble floor buffing machines in many ways. Contractors perform the process to attain the required initial specified gloss readings for a floor. The owner's maintenance staff uses them to restore the gloss value as customer foot traffic abrades the finish. The process of insallation and maintenance has minimal effect on the original hard-trowel finish.
What to look for when you buy
With so many choices it's hard to know what products are best. At the same time, it's important to keep up with the latest developments. Here are some suggestions about how to do this.
- Learn as much as you can from your supplier about recent developments in technology. Good suppliers have knowledgable employees.
- Ask about hybrid resin pads for grinding and honing operations. Technical developments in this area are constant and can increase your productivity.
- Inquire about diamond density and the quality of diamonds used. Remember, mixes of quality can increase productivity on some types of concrete.
- Few pads rated for wet grinding also can be used for dry work, but dry-rated pads will do either in most cases. If you are dry polishing, make sure you purchase the correct pad.
- If you are diamond polishing overlay cement, buy pads designed for that work. Latex resins in overlays can cause polishing problems.
Online: For more information on this topic, visit the Web sites of the Concrete Polishing Association of America (www.concretepolishingassociation.com), HTC (www.htc-floorsystems.com), and 3M (www.3mfloorprotection.com).