 |
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| Polymer overlays cure
so quickly that they can be stained and finished a day
or even hours after they're applied. Here, acid stain
sprayed onto the surface leaves a pleasing rnottled effect.
Note the decorative grid of scored control joints. Though
it looks like a colored slab, the concrete topping is
only 1/2 inch thick. |
Coloring
and Top-Coating
There are many decorative options. One of the most popular
with our clients is to treat the partially cured surface with
add stain. This produces subtle variations in color. Integral
color can also be created by adding pigment to the overlay
before it's applied,. or dry color hardener can be worked
into the topping after it has been spread and troweled.
Similar techniques are used to color
conventional concrete, but because polymer overlays cure so
fast, you can complete a job in much less time. For example,
a conventional slab is supposed to cure for 21 days before
acid stain is applied. We know from experience that we can
do it sooner, but if we do it too soon, the stain Will eat
away the surface layer of cement and expose the sand. By contrast,
we can add-stain a typical polymer topping the day after it's
applied. Some overlay products have to be stained within a
few hours after application; otherwise, the fully cured material
will be too dense for the stain to take. When that .happens,
the colors are not as bright or intense as they could be.
Sometimes we lightly sand the floor to open up the surface
so it will accept the stain. The sanding also removes minor
blemishes like popped air bubbles.
Acid stain can be brushed, sprayed,
or rolled onto the surface. We allow it to sit for 8 to 12
hours, then wash it off and neutralize it with water that
contains baking soda or ammonia. We then rinse the surface
with clean water and allow it to dry before applying a clear
sealer coat. A basic sealing job is done with wax or acrylic
lacquer. A top-of-the-line job gets a coat of waterborne epoxy
followed by a coat of polyurethane resin and multiple coats
of acrylic wax.
Polymer toppings cost $1 to $2
per square foot for a 3/8-inch layer. Self-leveling material
is typically more expensive than trowel-grade material because
it contains costlier types of polymer. Pre-mixed bagged overlays
contain everything except the water, so they cost more than
the material you make by adding liquid polymer additive to
dry ingredients such as Portland, sand, and aggregate that
you supply yourself. Installation labor runs about a dollar
or two per square foot, including a basic decorative treatment.
The final price would include an additional markup for overhead,
profit, and the degree of difficulty for the particular job.
Tom Ralston is a third-generation
concrete contractor in Santa Cruz, Calif. Photos for this
article were provided by Tom Ralston Concrete.
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