The Basic Principles
of Crack Repair on Slabs
Don't
make conditions worse
If the crack is of hairline width,
it is usually better to leave it alone. For
additional protection against deterioration, apply
an epoxy coating over crack.
Cut out only when necessary
If the crack snapped
cleanly, with no islands, and if the edges of the
crack have not spalled, merely
fill the crack with a proper epoxy (semi-rigid).
Cut out as narrow as possible
Don't use
a cutting tool (router, etc.) that will create a
1/2" wide repair of a 1/8" wide
crack.
Cut out deep enough
When cutting
out cracks, always go at least 1/2" deep
to provide enough "bite" for the epoxy
along the joint walls.
Don't weld the crack
Most cracks
in slabs-on-grade do not present structural problems.
Welding the slab
together at the crack
may merely result in another crack occurring adjacent
to the first. Use a semi-rigid epoxy for most crack
repairs, especially for the first two years.
Don't
feather-edge repairs
To feather
means to taper to -0- thickness. Instead, create
a vertical edge of
at least 1/2"deep
on all crack repairs.
This infomation
was taken with permission from the Web site of
Metzger/McGuire, a manufacturer of epoxy
and polyurea joint fillers and repair products. For
more information on crack repair, visit www.metzgermcguire.com. |
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Basic crack-repair procedure includes
widening and smoothing out the edges of a crack, either with
a chisel or a crack-chasing saw; thoroughly cleaning out
the crack; applying a primer, if your crack repair material
calls for it; then applying the crack repair material.
Three types of repair material
Crack repair materials range from rubbery caulks that you
can stretch with your fingers to steely acrylics that you
can't drive a nail through. New crack repair materials
come onto the market all the time. But basically they all
fall into three categories: flexible, semi-rigid and rigid.
Flexible crack repair materials are typically used in joints
and in structural cracks that move like joints. They stretch
and compress as a crack moves, and they do nothing to restrict
that movement. While flexibles don't technically "repair" cracks
in the sense of bonding them together, they're great for
weatherproofing. They're disastrous beneath a cementitious
overlay, but they are sometimes used beneath some non-cementitious
elastomeric coatings. "They might work with an elastomeric
topping, but with a cementitious overlay you're almost guaranteed
to get a crack," says Ed Diaz, senior technical service
specialist with Sika Corporation. Flexibles can typically
be found in a wide range of colors.
Epoxy-based crack repair materials are the industry standard
for reducing or eliminating a crack's ability to move.
Rigid epoxies are used for structural repairs where the
concrete needs to be solidly fused back together, returning
the cracked concrete to its monolithic state. Rigid materials
make repaired
cracks stronger than they were before they cracked. They
can be troweled in, like other crack repair materials, or
applied with a low-pressure injection system. Injection systems
require specialty equipment, and often a specialty contractor,
but they offer the best guarantee that a crack will never
crack again. Crack injection is the standard approach for
structural repairs.
Semi-rigid epoxies are most widely used for repairing cracked
concrete for decorative applications, and they're commonly
used beneath cernentitious overlays. Semi-rigids allow for
rapid turnarounds on crack repairs, as well as repairs that
are perfectly flush with the floor, since excess cured material
can be shaved off.
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