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Concrete Decor - Index

Concrete Decor - Concrete Decor Magazine, The Journal for Decorative Concrete - Index

Rules of Contraction”) to control cracking.
Placed on the surface of concrete slabs and
created by forming, tooling or sawing,
these joints weaken the slab to provide
attractive avenues in which cracks form.
Cracks formed inside these joints are
relatively easy to disguise.
Placing contraction joints in
concrete is not exactly rocket science.
While care must be taken in the joints’
design and creation, three fundamentals
come into play. First, maximum joint
spacing should be 24 to 36 times the
thickness of the slab, with a maximum
spacing of 15 feet. Second, the
minimum depth of a joint should be a
fourth of the thickness of the concrete.
Third, all panels created by contraction
joints should be as square as possible.
Harder than rocket science
Those involved in decorative
concrete may fi nd themselves at odds
with square or rectangular contraction
joints. They may be working with
circular slabs and not wish to break
up the fl ow of the surface with straight
angles. Radial shapes such as those
found around fountains or graceful
fl owing lines around swimming pools
seem to invite curved contraction joints.
Installing shallow, decorative
joints may be as simple as grinding the
surface with a router. But placement and
installation of curved contraction joints
isn’t easy.
“You’re usually going to see curved
joints in a radius or another layout that
the architect establishes to go along with
whatever type of theme or architecture
they’re employing,” says Mike Riggs,
president of Phoenix-based Progressive
Concrete Works Inc. “We use curved
contraction joints when we’re trying to
tie the design of the building and the
hardscape. The curving lines become
part of the overall architecture of the
building.”
It’s not always easy to control cracks
in curved or radial joints, Riggs says.
“Concrete typically likes to crack
in a square. A good rule of thumb
when you’re dealing with square or
rectangular shapes is if you’ve got a 10foot-by-10-foot
slab, you’re okay. If it’s
a 10-foot-by-20-foot, it’s going to want
to crack right down the middle of the
rectangle.”
Dec. ’07/Jan. ’08 | www.ConcreteDecor.net | 73