Polishing concrete is tricky. You must determine the right number of passes to make with the just the right tools. Doing too much wastes valuable time and tooling. Doing too little can compromise the result and disappoint the client. It takes years of experience to find the right balance.
The CRMX 3-Step Polishing System from GMI Engineered Products LLC of Bluffton, Ohio, is designed to eliminate that learning curve.
Introduced in 2010, it’s the first application of a wet polishing process common in high-precision metalworking, optics, dentistry, and other high-precision industries to concrete: free abrasive polishing. Instead of being embedded in rotating pads fixed to the bottom of a machine, abrasive particles are suspended in a liquid that’s applied to the surface before polishing.
Once any floor is prepped, you use the same three tools and the same three chemicals to achieve a high-gloss finish about 40% faster than conventional polishing. Derived from “concrete reinforced matrix,” the CRMX tools adapt to equipment ranging from auto scrubbers to floor buffers to large planetary grinders.
The system produces results through the interaction of tools and chemicals. The combination of heat, pressure, and motion parallel to the surface deforms the surface concrete, bending over high points and filling in low points.
The system uses an electronic device, the texture meter (also called a t-meter or contact stylus profilometer), to ensure quality. By taking readings throughout the polishing process, contractors can tell when they’ve achieved the result required at each step.
Then, and only then, do they move on to the next step.
According to Andy Bowman, who developed the system and t-meter for GMI, reducing the complexity of the polishing process is one of its principal benefits. He’s the former chair of the Concrete Sawing & Drilling Association’s Polishing Committee, which released Standard ST-115 (Measuring Concrete Micro Surface Texture) in 2013. ASTM is developing a test method for the standard.
“In conventional polishing, the hardness of the tool matrix has to be the opposite of the hardness of the surface,” says Bowman, who now develops concrete-related products for Betco Corp. of Bowling Green, Ohio. “You choose hard bond, medium bond, and soft bond tools depending on how hard the concrete is. Matching those things up is complicated.
“This system isn’t tied to concrete hardness. Instead, the polisher always uses the same three tools. We take the decision-making out of the hands of the operator on the jobsite and allow management to maintain control, even from 500 miles away.
“When polishers are being trained, they always ask ‘how long do you run this tool?’ We give them a number the t-meter must record. That qualifies the surface and says it’s OK to move to the next tool. Every tooling change is quantified by the texture that’s recorded at the concrete surface.”
GMI offers a two-day decorative concrete class at its Ohio headquarters and through distributors across the country. A week-long certification class goes into more depth on concrete technology and includes more specific training on the t-meter.
There are about 140 certified contractors across the U.S.
Prep, then polish
As with any concrete polishing process, the CMRX system depends on proper preparation. Both new and existing slabs generally need some preliminary grinding to even out the surface, remove previous finishes, and/or expose the desired amount of aggregate.
GMI makes a line of prep tools designed to accomplish any of these goals, but contractors can also use conventional tools they already own.
Three tools for three roughness levels
The t-meter is used to measure surface texture at each of the three steps and calculate roughness average (Ra). A reading of 100 Ra indicates a honed finish; zero indicates a mirror-like finish.
In Step One, the concrete surface is saturated with water and CRMX Surface Refining Agent is applied. This liquid, which contains the free abrasive particles in suspension, can be spray-applied or poured onto the floor. For large projects, some contractors put the liquid into an auto scrubber and apply it with that.
Once the liquid is on the floor, attach the metal Step One roughing tool to the polishing machine and make multidirectional passes across the floor. If the chemical dries out during the process, you can rewet the surface and it remains effective.
When Ra reaches 97.9, Step One is complete.
Leaving the chemical slurry on the floor, switch to the composite Step Two tool and continue polishing to refine the surface. When the t-meter registers Ra 28.05, Step Two polishing is complete.
By then, the chemical slurry typically will have formed a gel or paste. Remove with a squeegee, scraper, or slurry vac; allow to solidify overnight; and dispose as you would any nonhazardous waste material.
Next, the floor is thoroughly washed, usually with an auto scrubber, and allowed to dry. Once dry, apply the Step Two liquid, CRMX Densifier, a colorless liquid that hardens and dustproofs the concrete.
When the densifier is thoroughly dry, switch to the epoxy-resin Step Three tool and dry polish the floor. The target Ra for Step Three is 4.25.
The final application is CRMX Acid Blocker, a chemical agent designed to produce an ultra-hard, watertight, and dust-repellent surface. When the acid blocker has dried completely, the floor is burnished with a non-diamond high-speed burnishing pad.
A contractor's perspective
Prep Concrete and Construction in El Dorado, Calif., has specialized in grinding and polishing since its founding in 2007.Projects range from custom homes and schools to office buildings.
After years using mainly dry polishing methods, owner Matt Bowen added CRMX to his repertoire in 2014. He uses the system when he can to reduce labor costs and diamond tool expense.
“I tend not to use it on residential jobs if there’s already trim installed or cabinets that you have to cover up to keep from getting wet or splashed with chemicals,” he says. “Also, using a wet system can be a problem if there are other trades walking around where you’re trying to work.”
But when a floor’s wide open, the process is faster and more accurate than traditional polishing.
“Anytime we can run wet, it definitely saves us time,” Bowen says. “It’s harder to see scratches with a wet system, so using the t-meter every so often during each step ensures you’re getting the required Ra rating. I can tell my guys, ‘Use this tool and go at this speed to polish this room.’”
Prep work like crack repair and glue removal usually requires an aggressive diamond tool with a 25, 35, or 70 grit profile. Even with a new floor, a diamond tool is necessary if the client wants more aggregate exposed than a cream or salt-and-pepper finish.
“But once you get the prep work done, using the Step One tool with the chemical takes a lot of the guesswork out,” Bowen says.
“I’ve done at least 50,000 square feet over two years and the Step One tool still has life left in it. By eliminating the 40, 80, 100, and 120 tools I’d use on a typical dry polish, I’m saving time.
“The Step Two tool doesn’t last as long. You might get 1,000 square feet or 2,000 square feet out of it, but as a polishing contractor you don’t worry too much about the tooling cost. Labor is a bigger factor.”
Product developer Bowman says contractors typically spend $1 to $1.25 per square foot on tools and chemicals for conventional polishing. The CRMX system is about $0.60 per square foot.