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A burning question
To burnish or not to burnish? It all depends on the look you’re after
by Stacey Enesey Klemenc
Bob Harris, director of product training for the Scofield Institute, the educational arm of L.M. Scofield Co. in Douglasville, Georgia, explains that when burnishing involves a hand trowel: “With each successive pass, you use a smaller tool. The smaller the trowel the more weight you can apply to densify the surface. You’d start with, say, a 20-inch trowel then a 12 then an 8-inch burnishing trowel. That’s probably as small as you’d typically go. Obviously, this method wouldn’t be practical for large jobs.”
When you burnish, you’re making the surface slick and very smooth, as well as altering the color. “Burnishing creates a very nonuniform look, kind of a marbleized appearance where the color darkens in certain areas,” Harris says. “Some people call it a ghosting effect.”
If you’re selling this look, it can be very attractive, but if someone wants a monochromatic surface it’s not the way to go.
Bob Ware, president of the Decorative Concrete Store in Cincinnati, agrees with Harris’ advice and cautions contractors to be careful with integral colors. “The term burnishing, in essence, means burning the finish. Trowel machining colored concrete is a careful process. It may only require one to two passes.”
If you do more, instead of a high gloss, “you’ll end up with streaks marks — or worse, black marks — from the trowel machine, tinting the true color you really want.” So the final pass of many colored concrete floors is hand troweled by a crew on kneeboards.
To be on the safe side, a preconstruction meeting should be arranged between the finisher and the architect to decide on the look of the floor. If the job is large enough, Ware urges, pour an 8-by-8 foot mock up for the architect’s approval.
To be successful time and time again, Bouknight — whose mantra is “perfection, not production” — notes it’s very important to find a ready mix supplier who’s cognizant of what you want to achieve and is involved in helping you achieve it. “When we create a floor that’s stunning, I call the supplier and tell them they must see for themselves what we can do with these materials,” he says.
“The color chosen limits the degree of how much you can burnish the floor,” Bouknight says. Each trowel pass darkens the floor so if the floor is, for instance, a really light beige color you can burnish it in a subtle way. However, you’ll have to sacrifice a really tight and smooth finish or you may wind up burning the cement in places. “The more you trowel, the more radical the background color becomes. You really have to pay attention and make sure you don’t overtrowel. Typically, light integral colors don’t work well,” he says. “Reds work well if you’re careful.”
Bouknight says he always uses a machine to burnish floors. Depending on the application, these machines can weigh anywhere from 50 to 200 pounds and can be fitted with different shoes and blades. “A guy with a hand trowel can get a smooth surface but it will look monochromatic,” he says. “You won’t get the subtle, variegated, marbleized look that you get with a machine.”
Sound concrete finishing practices and using the right tools make all the difference, says Bouknight. He recommends having your machines serviced at least three times a year and to make sure everything is balanced. “Maintenance and cleanliness of equipment is very important to a successful job,” he stresses.
Matt Casto, vice president of technical services for Bomanite Corp. in California, says the mottled look has become more prevalent with the introduction of polymer-modified micro-toppings. “The thinness of the material has made it very cost effective to blend colors together,” he says. “You can put down two to three colors quickly and mottle them together by dragging them on, brushing them on or spraying them on.” And now there’s another option: you can “HoverTrowel” them.
Makers of HoverTrowel, a pneumatic-driven power trowel initially developed to finish decorative aggregate epoxy floors, are working with a number of manufacturers to establish a niche in this market with accessories and modifications designed specifically for overlayments. Industry experts are experimenting with various RPM and torque-load motors with weights to determine the optimum method and timing for these polymer-modified applications.
According to Drew Fagley, president of HoverTrowel Inc., this power trowel can be used in lieu of hand troweling or on occasion in place of conventional trowels. “The resulting finish is consistently uniform and flat,” he says.
Fagley sees the machine as a big plus when hard troweling multiple colors into a surface. Conventional power trowels are too heavy for some surfaces or don’t achieve the desired effect, he says, so crews currently finish the job by hand. It’s in these instances that the lightweight HoverTrowel is finding success. The machine can be used effectively to hard trowel in colors, thus reducing manpower and finishing time. “Instead of six guys going out with kneeboards, we can outfit an operator and a support man with float shoes we call slides — which are basically kneeboards for your feet.”
Various types of motors are available to supply different torque loads for the more resin rich systems as well as today’s newer polymer toppings. Additional weight, in 2 pound increments up to 22 pounds, can be added to further fine tune the trowel’s performance.
In addition to the standard tool — steel blades, stainless-steel and composite blades are available — as well as various float blades made of mahogany, magnesium, aluminum or laminated resin-to eliminate unsightly burnishing marks and to produce various finishes.
“About the only thing you can’t change about the HoverTrowel are the results,” Fagley says with a laugh. It has an extension handle that doubles its length in six-inch increments. Two different diameter guards are available to complement the multiple blade and float sizes. And soon a four-cycle retrofit motor will be on the market.
“We’ve played around with the HoverTrowel and I believe that it’s going to be a good tool to burnish micro toppings with,” says Bomanite’s Casto. “It’s lightweight and has the ability to get onto that material quickly.”
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Machinery on the horizon
