Condo Media - October 2013 - 16

by Jack Carr, P.E., RS, LEED-AP

C A I

R e g i o n a l

N e w s

MAINE

Water Down Below
Steps for Preventing Basement Leaks

et basements are an annoyance not just to unit
owners but also building
committees and property
managers. Just when you think it is
only an intermittent problem, along
comes a Patriots’ Day storm and everyone wants to build an ark.
Fixing a wet basement can be complicated because not only is the source of
the problem not well known but selecting the method of repair can be more
complicated than buying life insurance.
An additional worry may be that there
is not only a water inﬁltration problem
but also a structural problem.
To simplify our discussions, let
us only consider relatively modern
basement foundations of monolithic
poured concrete, as repairing stone
or masonry foundations can be more
complicated. Typically, a basement
foundation is made up of a concrete
spread footing pad many feet underground supporting a concrete basement wall. Most of these types of
foundations have foundation drain
pipes around the exterior perimeter at
the footing and some buildings have
foundation drains under the basement
slab. These pipes drain to the outside
by gravity or to a sump pit and pump.

Addressing the Problem

When basement water inﬁltration is ﬁrst
observed, the initial reaction should be
to control the easiest source of water,
i.e. the ground surface. If the roof has
gutters and downspouts, make sure
the downspouts release the water ﬂow
10 feet away from the foundation. On
the ground at the drip edge, ensure the
ground slopes away from the foundation. Place a sheet of polyethylene on
16

CONDO MEDIA • OCTOBER 2013

the ground 18 inches wide along the
foundation and cover with stone or other
material to hold the membrane in place.
The easiest foundation leaks to ﬁx are
the wall cracks that show signs of dampness or mineral efﬂorescence. These
vertical cracks are rarely of structural
concern and can be easily sealed by professional companies who drill holes in
the walls and inject a poly or epoxy ﬂuid
ﬁlling the cracks. This technique is fairly
inexpensive and produces good results.
More challenging is when the water
inﬁltration comes through the joint at
the base of the foundation wall. This
would indicate the positive pressure on
the ground side of the wall is higher
than the negative pressure on the basement side, overwhelming the foundation drains 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,
causing the wall to bleed or sweat.
• The ﬁrst thing to do is have a plumber
ﬂush out the foundation drain pipes,
as sediment can bypass the ﬁlter cloth
wrapping the perforated drain pipe
and clog it up. If ﬂushing does not
work, then three repair methods are
often offered. The simplest is coating the wall with a thick water-sealing
product. 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 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
of the interior wall. Holes are drilled
through the base of the wall. The
trench is ﬁlled with stone, and one
of several manufacturers’ drain pipe
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 backﬁll 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 that directs 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 ﬁle away your plans for an ark. CM
Jack Carr, P.E., RS, LEED-AP, is
senior vice president with CriteriumEngineers in Portland, Maine. He is
a member of the Condo Media board
and a frequent author and speaker.

Condo Media - October 2013

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