Decorative Floors With Polymer Overlays,
Mixing and Applying Polymer
Like conventional concrete, polymer concrete is made by mixing
wet and dry ingredients. Some overlay products come bagged in
dry ready-mix form, with the polymer already in the dry
ingredients — all you add is water. In other cases, the
polymer comes in a liquid form and is field-mixed with water
and typical dry ingredients — cement and sand, as well as
crushed stone or aggregate when the overlay is exceptionally
thick. We use such a thick overlay when we're leveling floors
that are seriously out of whack. Some products can be built up
in layers, but it's easier to do a continuous pour and put
aggregate in the material that goes in the low spots. This is
possible because overlay is mixed on site in small
Polymer toppings cure quickly, which is a major selling point
when there's not much time to do the job. Some of the products
I use can support foot traffic in 3 or 4 hours and develop
compressive strengths of 3,000 psi in 3 hours, 6,000 psi in 24
hours. Overlay products come in two types, trowel-applied and
self-leveling. It's usually more economical to use
trowel-applied toppings: They generally cost less up front, and
unlike self-leveling products, they can be applied in a thin
even coat. It usually takes more material to do a self-leveling
overlay because the topping might be 3/8 inch thick at one end
of the room and 3/4 inch thick at the other.
Spreading self-leveling toppings (left)
has to be done with care. It's important to work out any air
bubbles, but the material shouldn't be touched once it starts
to set. A gauge rake (right) is a handy tool for spreading
trowel-grade material. Adjusting the wire bales on each end
raises or lowers the blade, making it easier to spread an even
coat of material.
Trowel-grade materials also have longer working times; some can
be stamped or textured before they set. To maintain a
consistent thickness, we spread the overlay with a gauge rake
or notched trowel. Afterward, we go over it with a regular
trowel to produce the texture and finish we want. Some
trowel-applied materials are referred to as microtoppings
because they can be applied in layers as thin as 1/16 or even
Self-leveling overlays set up very quickly, which makes them
tricky to use. It takes some experience to know when to stop
spreading self-leveling overlay. The material starts to set in
10 or 15 minutes, so you have to work fast to maintain a wet
edge as you work your way across the floor. Spreading puts the
material where you need it and removes air bubbles that can
cause imperfections. But you shouldn't touch the surface after
the polymer starts to set. If you do, it leaves a mark that's
hard to repair. If you do it right, the floor will be dead flat
and have a glossy sheen.
Self-leveling overlay is soupy when it's wet, so you should
make sure there are no leaks or holes in the substrate. We
recently missed a small nail hole in a bathroom floor and ended
up with a cone-shaped depression where the overlay leaked out.
We happened to be using a product that's difficult to patch.
The client was very particular, so we ended up tearing out and
redoing that part of the job.
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 acid
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.
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 mottled 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.
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 acid-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 Ralstonis a third-generation concrete contractor
in Santa Cruz, Calif. Photos for this article were provided by
Tom Ralston Concrete.