Page 634 - 2018 National Home Improvement

2018 National Home Improvement Estimator, All Rights Reserved Page 507

Cosmetic repair of earthquake damage such as surface cracks, nail pops and minor misalignment
doesn't require a building permit in most communities. But some building departments require a permit if
the cost of cosmetic repairs exceeds a specific percentage (such as 10 percent) of the cost of a new
wall or ceiling.

Repair of Foundations and Floor Slabs
Cracks up to 1/32" wide (less than the thickness of a dime) in concrete and masonry are usually the
result of shrinkage and are more a cosmetic issue than a structural risk. No repair is required. Wider
cracks in patios and walkways can be repaired by grinding away raised edges and filling gaps with
mortar mix. Where load-bearing capacity is important, such as in a driveway, floor slab or foundation,
structural repair may be required.

Cracks in concrete can expose steel reinforcing embedded in the concrete. Steel exposed to the air will
corrode. Badly corroded steel reinforcing or foundation bolts can result in structural failure. Corroded
concrete reinforcing may be a more serious structural problem than fractures in the concrete itself.
Fortunately, there's a good way to prevent corrosion and restore the load-carrying capacity of most
concrete foundations and slabs.

After the Northridge, California earthquake on January 17, 1994, several insurance carriers agreed to pay
for concrete crack repair done with injected epoxy. At the time, these repairs were controversial. In
1994, no structural testing had been done on reinforced concrete repaired with injected epoxy. Today,
we know that injected epoxy can restore the original load-carrying capacity of concrete foundations and
slabs with cracks up to about 1/2" in width. Cracks wider than 1/4" may require pre-packing with sand
or aggregate.

Epoxy Injection
Before starting work, inquire at your building department about any special requirements. Your building
department may require a building permit or other documentation for structural crack repair with epoxy.

Repair starts by drilling injection ports every 4" to 8" along the crack. Port depth depends on thickness
of the concrete. Most slabs are 4" thick. Foundation stem walls are usually 8" thick. Spacing and
diameter of the ports depend on the width of the crack and the thickness of the concrete. Tighter cracks
and thicker concrete require more ports. The drill should have an attached vacuum system to keep
concrete dust out of the repair area. When drilling is done, flush the crack with a stream of water or an
air blast. Place a plastic injection cap over each drilled port. Then seal the entire surface of the crack
with epoxy gel. When the gel has set enough to seal the crack, begin injecting epoxy resin through the
port caps using a binary caulking gun. High pressure isn't required. A thin mix of epoxy will penetrate
very small cracks even in cold weather. Start filling ports at the lowest point. Inject epoxy until material
begins to flow out of an adjacent port. Then move on to the next port.