A burning question
To burnish or not to burnish? It all depends on the look you’re after
by Stacey Enesey Klemenc

For many years, burnishing has been commonly used to make commercial floors harder, more durable and easier to clean. But these floors had no aesthetic value. They didn’t need to; they were an underlayment.

“In the old days, they burnished concrete for structural value,” agrees Tom Ralston, president of Tom Ralston Concrete, a third-generation concrete company in Santa Cruz, California. “The more you trowel concrete, the harder and the more abrasive-resistant it becomes.”

But in addition to this incredible hardness, something else happens to the surface’s appearance, says Ralston, a frequent speaker and trainer of decorative concrete techniques at industry gatherings. “We found that burnishing really mimics acid staining in that it creates a kind of patina-like variegation that people are looking for these days.” He recalls one client who wanted a variegated-looking countertop some years back. With the help of a spray bottle, “We found we got a nice variegation with gray natural concrete just by adding water.” The more they burnished — with a burn trowel typically three inches wide — the more variation of color they got.

Ralston, who is always scouting for new products and techniques to help him with his one-of-a-kind creations, was definitely onto something that went beyond the basic burnishing of yore.

The highs and the lows
When you trowel over and over again-which is what burnishing is-it makes for a shiny, smooth and hard surface, a look that people today want for their interior floors and countertops.

Rather than for the shine, Ralston says he burnishes to get the “highlights and lowlights” of naturally colored concrete or color applied to the concrete via a hardener. “If you extend the concept of burnishing to include color hardeners that allows you to open up a whole array of visual possibilities.Your trowel then becomes similar to that of an artist’s brush. You could make colored concrete look like an oil painting.”

And cutting-edge contractors like Ralston are finding out that if you flash in color as you employ these burnishing techniques you can create masterpieces.

It’s all in the blend
When you hard trowel colors together, you’re actually blending them for a more natural look, Ralston says. “Look at a piece of natural slate, stone or bark and you’ll see a subtle blending of colors. That’s what you’re trying to accomplish with your trowel. You’re burnishing for the visual effect, not to create a scratch-resistant surface or a surface that cleans easier.”

The more you trowel, the more mottled the coloring appears — which isn’t always a good thing. When you overtrowel integrally colored concrete you may end up giving clients a mottled effect rather than the color-consistent surface they wanted. And if you really overtrowel hard concrete — and this is especially true with power trowels — the aluminum in the mix and the steel in the blades can get so hot it will burn and blacken.

Going through the steps
Alan Bouknight, owner of Azzarone Contracting in Minneola, New York, has been burnishing concrete for nearly 10 years. In the last year, he says, his company has made a “quantum leap” in perfecting the process, thanks in part to new tools, new techniques and being smart enough to learn from mistakes. “We’re willing to see how far we can push the limits of concrete,” he says. “It has an inherent beauty if you know how to coax it out.”

For a burnished finish — “The right terminology is a hard-steel-trowel burnished finish” — first strike the surface with a straightedge to make sure it’s fairly level, pass with a bull float and, when the concrete is ready, come in with a machine and hit it once or twice with shoes or pans to flatten it, says Bouknight. The drag from the oversized shoes works the fines and the cream to the surface while the vibration of the machine shakes the mixture and the heavier aggregates sink. The oversized shoes help to distribute the material and fill in the hills and valleys.

Next, remove the shoes and go over the surface with your stainless steel finish blades to help create a polished finish. During each stage, the concrete keeps getting harder and harder and you must determine when — and if — to get on it again. Each time you machine trowel, you need to increase the speed and pitch of the blade, Bouknight says, because you’re building up friction and heat with the drag and that can help burn the floor.

A pattern is also important. “You need to go in different directions so you won’t get waves in the floor; you want it to stay flat. Typically, you make passes like north to south and then east to west to give you nice coverage between coats. It’s a lot like painting,” says the seasoned contractor.

The method he just described, he says, will produce a burnished — almost marbleized metallic-look to the floor.

Burn, baby, burn
Bouknight remembers when the standard for finishing concrete floors was to give the client a burnt floor. During his boyhood, he recalls accompanying his father or grandfather to jobsites in New York City some evenings and “You could see sparks fly off the blades. That’s how many times they’d trowel it.” Burnt floors are hard as steel, he explains, and it didn’t matter if they were blackened. “The floors were going to be covered up with carpet or linoleum anyway.”

Today, “We don’t have to burn the floor as much because we have plenty of additives to make it strong. We can avoid the burn and get a beautiful opulence. Each time you make a pass, you’re layering the burnish marks, which gives a sense of depth to the floor. It may look rough or coarse, but it feels like hard silk.”