Condo Media - November 2023 - 29

● Foundation Joints
More challenging is when the
water infiltrates through the joint
at the base of the foundation wall.
This indicates the positive pressure
outside of the wall is higher than the
negative pressure on the basement
side. This condition will overwhelm
the foundation drains, which are
designed to reduce hydrostatic pressure
by diverting water away from
the wall. The ground water is finding
a path either under the footing and
through the slab or through the joint
between the footing and the wall.
In concrete block walls, the water
can even be driven vertically up the
wall core, causing the wall to bleed
or sweat.
The first thing to do is have a
plumber flush out the foundation
drainpipes as sediment can bypass
the filter cloth wrapping the perforated
drainpipe and clog it up. If
flushing does not work, then three
repair methods are often used. The
simplest is coating the wall on the
interior side with a thick watersealing
product. However, these
products often fail, especially the
one-part coatings, as they do not
address the real problem, namely,
the hydrostatic pressure trying to
lift the coating off the wall. Some
of the modern two-part crystalline
coatings not only fill the small
cracks with expanding crystals but
also penetrate the concrete to hold
better to the surface.
A second method also addresses
the problem from the basement
(negative pressure) side by installing
a " baseboard " drain system at
the base of the interior basement
wall. A trench is cut in the concrete
floor slab a few inches wide along
the entire perimeter, and holes are
drilled through the base of the wall.
The trench is filled with stone, and
one of several manufacturers' drainpipe
systems is placed in the trench
and connected to a sump pit and
pump. The trench is then covered
by concrete level to the existing slab.
The third repair method is to excavate
the soil next to the foundation
wall to repair the positive pressure
side of the foundation wall. Once
the soil is removed to the footing,
the foundation drain is repaired or
replaced with a modern waterproof
membrane applied to the wall with
a drainage plane fabric directing the
water to the new foundation drain.
This method can be combined with
the interior " baseboard " method.
This is expensive and disruptive
but is a very effective technique.
The key to a successful dry basement
project is selecting the right
method for your condo's conditions
and the right contractor to execute
the plan. With some understanding
of the causes and remedies available,
you will be able to weather the next
rains to come.
■ JACK CARR, P.E., LEED-AP,
IS SENIOR VICE PRESIDENT WITH
CRITERIUM-ENGINEERS IN PORTLAND,
MAINE. HE IS A MEMBER OF THE
CONDO MEDIA BOARD .
Banking that treats you like a
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DPicha@southshorebank.com
781.682.3243
November 2023 CONDOMEDIA 29
Condo Media - November 2023

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