Despite the simple, rugged nature of the material, concrete
counters have become very popular in high-end kitchens and
baths. Some homeowners choose this material because it can be
produced in any color or texture they want. Others just like
the way the product looks: Because they're crafted by hand, no
two concrete counters are ever exactly the same.
Concrete counters can be cast in place or fabricated in a shop.
Shop methods place a premium on carpentry skill, while casting
counters in place requires better concrete-finishing skills. I
own a concrete company that specializes in decorative finishes.
Since we have many good finishers, we usually pour counters in
Shop-fabricated counters are produced off site, then
transported to the job and installed in the same manner as
granite slabs. They're poured upside down and cured in the
form; the shape and texture of the finished surface are largely
determined by the form.
Cast-in-place counters are poured right side up, so the shape
and texture are heavily influenced by the finisher. First, a
continuous plywood top is installed on the cabinets; edges,
penetrations, and overhangs are temporarily formed. Reinforcing
is then installed, and the concrete is placed. As soon as the
concrete starts to set, the edges are stripped and the visible
parts of the counter are hand-finished with the same tools and
techniques used for other kinds of concrete flatwork. You can
float, trowel, grind, or use textured mats to finish the
A matter of taste. Site-cast
and shop-fabricated counters are similar but not the same. A
shop-fabricated counter may be perfectly straight, flat, and
smooth. Site-cast counters may be extremely smooth, but they're
unlikely to be as flat or uniform as a shop-cast slab. It's
really two different looks. The subtle irregularities produced
by hand-finishing give cast-in-place counters a more
Finishes aren't the only difference. The forms for a
shop-poured counter are built from templates. If the template
is off, the counter won't fit. Also, slabs are hard to
transport, so large shop-fabricated counters are cast in
sections and assembled on site. By contrast, site-cast counters
can be monolithic pours, with no seams. Even the backsplash can
be formed and poured as an integral part of the top.
Most customers have no experience with concrete counters, so
it's important to tell them what to expect. We explain that the
color may vary slightly across the counter. It's possible the
counter will crack — we haven't seen a lot of it, but it
does happen. Thick counters are less likely to crack than thin
ones. Ideally, a counter should be at least 1 1/2 inches thick
at the thinnest spot. On occasion we've gone as thin as 1 1/4
inches, but we prefer to pour 2-inch counters.
Customers need to understand that concrete may stain over time.
They have an easier time accepting this if they know it's
coming and have been taught to think of it as the development
of patina. Counters can be sealed to prevent staining, but the
most effective sealers give the surface a shiny, resin-coated
look that some people find objectionable. A less obtrusive
sealer may provide less protection. People who want things to
look exactly the same five years down the road are poor
candidates for concrete counters.
We also warn homeowners not to put red-hot pans directly on
concrete: Extreme heat can cause it to spall.
Samples. By the time we get
the job, the customers have already seen samples from other
projects. They may want a slightly different color or texture,
however, so we'll pour three 2-foot-square samples. If they
want integral color, we tell them the samples will be close,
but not a perfect match to the color of the actual counter.
This is because samples are mixed in tiny batches; minor
variations in the proportions can affect the results. On the
other hand, surface treatments like dust-on color are easier to
On the day of the pour, we make additional samples from the
same batch of concrete that's going in the counter. We can then
experiment with the samples to show the customers what the
counter will look like when it's treated with various stains
and sealants (see Figure 1).
|Given the many ways to color and
texture concrete, no two counters are ever exactly
Forming the Counter
Concrete is poured on the plywood top (Figure 2). The plywood
edge is hidden behind a face frame or by thickening the nosing.
If the counter has any kind of overhang, we build a temporary
shelf to support the nosing when it's poured and while it
cures. The shelf can be anything; we normally put a 2x4 on the
flat and prop it up with legs. To avoid damaging the cabinets,
we wedge or clamp it in place.
Figure 2.As with any
counter material, it's easier to create the opening for
a drop-in sink than for an undermount sink. The author
uses a piece of rigid foam insulation board, patterned
from the sink template, to form the undermount
We typically need to remove doors or drawer fronts to
install the shelf. Before starting, we use blue tape and
plastic to mask the cabinets and nearby walls. If there's a
finished floor, we'll protect it, too. We cover the plywood top
and adjoining walls and cabinets with Kraft building paper.
This prevents them from absorbing excess moisture or wicking
color from the wet concrete.
Edges that don't butt to existing surfaces are formed by
fastening strips of wood to the temporary shelf (Figure 3).
Curved edges can be formed with 1/4-inch hardboard. Integral
splashes are formed by suspending a board just off the back
wall and parallel to it. The board is supported by temporary
legs, which can be removed once there's some concrete under the
3.The front edge is
formed by a strip of wood as tall as the counter is
thick. It's separate from the support shelf, so it can
be removed when it's time to finish the