| Prepping
and repair material options
No matter what decorative topping you're planning to apply
to the surface of the concrete - stain, opaque coating, bonded
or unbonded overlay - you need to make any crack repairs first.
The customary practice is to chisel or chase the cracks. Not
only does this help you clean up the edges of the crack, chasing
also provides a slightly larger slot in which to insert the
repair material.
 The
size of the chasing blade you'll need for the task depends
on the width of the crack, reports Jason Root, western region
products specialist with USF Surface Preparation Group in
Rancho Dominguez, Calif "A lot of people like to chase
the cracks with a V-shape or you can use a square-edge blade."
The typical blade widths used for chasing random cracks are
1/4-inch, 3/8-inch and 1/2-inch, he says, adding, "When
chasing a random crack, a smaller diameter blade is better.
The smaller the diameter of the blade, the tighter the radius
you can turn."
There are three general categories of
crack repair materials, explains Ronald Borum, executive vice
president of the Miracote Division of Crossfield Products
Corp. in Rancho Dominguez, Calif. Rigid repairs are referred
to as welds and the resulting repair is rigid. These materials
"replace the physical integrity and create a seamless
substrate." Epoxy and polymer cementitious fillers are
typical of this category, he says.
Products in the semi-flexible category
"are used more for joint sealing than crack repair,"
Borum says. "Because they're semi-rigid, they can tolerate
some movement. They're good under a coating that can tolerate
some movement, providing good support for the coating."
Flexible repair products are most commonly
used for minor crack repair - when the crack is 1/8-inch to
1/16-inch or less and the crack is stable. These products
bridge the crack, are gravity applied or spackled in.
In certain situations, you may need
to stitch across the crack. This technique generally results
in a strong repair, though it may not be pretty.
Which repair product you use is dependent
on the nature of the crack, additional steps you'll take to
relieve any ongoing stress in the slab (such as creating additional
control joints) and the decorative coating you'll be using
on top.
Terry Collins, concrete construction
engineer with the Portland Cement Association in Skokie, M.,
reminds contractors, "there's a constant volume change
happening all the time in concrete [as it expands and contracts].
If you lay the jointing out correctly, it provides a weakened
plane for a crack to follow versus a random crack."
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