Reinforcement: The Anti-Stress
Solution for Concrete Countertops
Concrete countertops
are works of art. They are also structural pieces of
concrete. Just as you don't have to be a trained artist
to create an aesthetically pleasing concrete countertop,
you don't have to be an engineer to build one that is
structurally sound - but it helps to understand the
physical stresses at play 'Reinforcement is one of the
most misunderstood topics in concrete countertops,"
observes Jethey Girard, a civil engineer and president
of The Concrete Countertop Institute. Too little, too
much - how much is just right? Unfortunately, there
is not a simple role of thumb when it comes to reinforcement.
Each concrete countertop has its own criteria: span,
width, thickness, load and the material properties of
the concrete itself What is critical to understand,
Girard says, is that "concrete countertops are beams,
not slabs on grade." He maintains that if you understand
where load, compression and tension occur in concrete
countertops you can figure out the appropriate reinforcement
design.
Types of Reinforcement
It's probably a good idea to point
out at the start that there are two kinds of reinforcement:
primary and secondary. Primary reinforcement you can't
do without. Secondary reinforcements can contribute
additional characteristics that may make a better product,
but are not absolutely necessary
Primary reinforcement materials are structural, plain
and simple. Rebar ladder wire and structural carbon
fiber grid are all primary reinforcement materials and
each has different characteristics and uses.
Conventional rebar is indeed a strong reinforcement
material, but for man), concrete countertop applications
it's just too big.
Conventional 3/8-inch, 1/2-inch or 3/4-inch rebar is
way too big for a typical 1 1/2-inch thick concrete
countertop, 'Girard explains. "No material more
than 3/16-inch in diameter should be used in a countertop
less than 3 inches thick.'
Michael Karmody, a founding partner of Stone Soup Concrete,
agrees that rebar is only useful in a situation where
you have a large volume of concrete. "We typically
pour 1-1/2 inches. Rebar takes up too much space and
can cause cracks."
The profile of the rebar or steel
used may also be important. Tom Ralston, president and
CEO of Tom Ralston Concrete, observes that smooth bars
don't grab to the concrete as well as ribbed bar.
Ladder wire and wire mesh are used by many concrete
countertop contractors, and for good reason: Both materials
are strong and small enough to use effectively in countertops.
The major differences are the overall shape and gauge.
Ladder wire is 9-gauge structural wire that is a narrow
parallel set of strands. Wire mesh is large, open mesh,
often 10-gauge in diameter, but there are heavier gauges,
such as 6-gauge, which is a larger diameter.
Mesh with enough steel in it to provide the required
tensile capacity is a very efficient way of reinforcing
large, simple stabs (such as rectangles), Girard says.
On the other hand, he points out, ladder wire is very
efficient for reinforcing complex shapes and around
sink holes, where the fixed spacing of welded wire mesh
would require extensive cutting and splicing. 'Both
can work together to make an, effective, efficient and
economical reinforcing," he says.
Ralston likes flat wire mesh because it is caster to
work with. "You Cut the shape you need and it can
be used throughout a monolithic unit," he says.
He has found that it is better to use 2.1 gauge for
more substantial reinforcing. "Also, you can address
the cornets and thinner areas with small, 1/4-inch stainless
bar that has been grooved with a grinder for better
bonding," he adds.
Structural carbon fiber is relatively new to the concrete
countertop trade. John Carson, director of commercial
development for TechFab LLC, explains that carbon fiber
was originally developed for the pre-cast industry and
used to produce CarbonCast pre-cast commercial building
systems. But use of carbon fiber has migrated to concrete
countertops because it has high tensile strength and
is thin enough to fit in tight spots.
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