 |
| Beyond the visual effects
burnishing can create with gray concrete, such graduations
of color can also make topical staining applications more
visually stimulating. |
Slight
of hand
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,
it 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.
 Take
care
To be successful time and time again,
Bouknight - whose mantra is it 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.
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