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Concrete Solutions to Cracking
By Lee Fleming
Special to The Washington Post
Thursday, July 27, 2006; Page H04
Because of ground movement and cycles of thawing and freezing, sooner or later any
sidewalk, driveway, patio or retaining wall will suffer cracking, buckling or breaking.
The question for the homeowner: Repair or replace?
Concrete
Christina K. Wilson is president of Renaissance Development, a District company
specializing in exterior masonry, including brick, stone and concrete. She compares using
concrete to baking a cake: You pour it, cure it, and end up with one solid piece. And when
it starts to break up under stress, not much can be done. "There's a fundamental
structural problem," Wilson says. "The temptation is to patch it, but you can do that five or
six times and the result will be the same."
What's more, the portland cement most homeowners get from home-supply stores to
repair the cracks will never match the original. Cement is just one ingredient in concrete,
along with sand and other aggregates. The resulting patchwork, says Wilson, is a
"Frankenstein fix."
When a concrete sidewalk buckles, a tree root is normally responsible, says Steve
Rodgers, masonry superintendent at American Professional Chimney & Masonry in Silver
Spring. In that case, both the portion of concrete between the control joints (cracks
between slabs) and the root have to come out, and the affected slab must be replaced.
Most pros say you're better off tearing up the whole thing when cracking and buckling
start. For one thing, in the past 30 years, building codes have changed. An old concrete
drive, for example, would not meet today's requirements. Old slab driveways may be only
1 to 2 inches thick, instead of the 3 1/2 to 4 inches common today. Many have been
poured over inadequate foundations that don't support and spread potentially damaging
forces. And if you have pooling on your pavement, eventually it will penetrate and break
down the materials through freezing and thawing, or leaching of harmful surface
chemicals such as salt. Sealants can do only so much to avoid the problem and are no
help against upheavals in the substrate that cause cracking. You're better off replacing
the drive or walkway segment with a new, properly graded and poured section.
To avoid problems such as pooling water, contractors will adjust the grade an
imperceptible but effective one-eighth to one-quarter inch per foot. They also dig deeper
foundations and use firmly tamped gravel and stone for a base.
Do it right, and your concrete walk or drive will last 30 to 40 years. A concrete aggregate,
with pebbles and small stones mixed in, offers maximum strength and durability.
Smooth-finish concrete, with a texture that looks like it has been lightly brushed, is fine,
too, but since it needs to be finished by hand, you'll want an experienced pro to do the job.
Concrete can be poured throughout the year, except during or after heavy rain, when
temperatures are extreme (32 degrees or below, or 90 degrees or above), or when winds
are 25 mph or higher.
Because the scope of repair or replacement jobs varies greatly, most professionals will
come out to give you an estimate. Costs for a concrete driveway run $12 to $16 per
square foot for the pour. This does not include removing old hardscape, excavation work
or the time involved in building forms.
Brick and Stone Masonry
David Wight, owner of Homeowners Masonry in Alexandria, finds that when it comes to
brick or stone, aesthetics determine whether homeowners patch or replace. "You make
your decision based on matching bricks and mortar," he says. For example, if even four or
five new bricks are placed in an older retaining wall, the fix will be glaring. "It's like a
dentist matching a tooth," Wight says. "You can find good old brick, and that's a start. But
you need to be able to match the mortar."
Homeowners can find an array of mortars at most home-supply stores. However, knowing
what type works best for different fixes and how to adapt mixtures to deal with complicated
conditions is usually best left to the pros.
Historic houses and their surrounding hardscape elements, such as walls and walkways,
pose a particular challenge. "On old brick walls, you need to use a historically accurate
mix of lime and portland cement -- 12 parts lime to 1 part portland -- which is weaker but
more flexible," says Wight, who has had more than 25 years of experience as a licensed
masonry contractor.
Jim Mock of L.C. Smith Brick in Alexandria and former president of the Masonry Institute in
Falls Church, says the primary requirement for paving brick is weather-worthiness -- the
ability to withstand freezing and thawing. "Lots of people have used brick from torn-down
buildings," he says, "but there's no test data on them and they can't be certified." Brick
that doesn't meet standards may pop out in a freeze. Because the Washington area has
frequent freeze-thaw cycles in winter, it's considered a severe weathering zone, with the
toughest conditions.
That's why masons should use a Type S mortar for pavers, Mock says. It is higher in
cement content than the lime-intensive mortar used in wall work.
American Professional Chimney & Masonry's Rodgers says a bigger threat to
hardscaping is salt. "Never put salt on any masonry work" for traction or to melt ice,
Rodgers says. "It will flake surfaces right off, even on new driveways." He suggests using
cat litter instead.
Many people put sealants on walkways and walls, but aside from giving a sheen to dry
stone, it doesn't do much to protect the surface.
You can expect to pay $25 and up per square foot for paved walks and patios, depending
on the paver material. This does not include the cost of hauling away old masonry,
building scaffolding or laying new foundations. That's why Wight of Homeowners Masonry
advises property owners to do preventive maintenance.
"Call a mason for $250 to $500 repairs when you see cracks in an entranceway, and
you'll save the $1,000 to $1,500 it will cost down the road," he says.
- Since 1981 -
