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TECHNICAL
38
T H E C A N A D I A N
HOME INSPECTOR
T
here has long been a misunderstand-
ing in the construction industry about
the terminology used to describe foun-
dation preparation in terms of damp-
proofing vs. waterproofing and the determina-
tion as to when each type of preparation would
be applied. Experience has shown that most
problems associated with foundation prepara-
tion (coating) failures were due to inaccurate
assessment of the local soil moisture conditions
and improper choices for adequate foundation
protection systems to match these conditions.
Misunderstood terms
“The two most misunderstood terms used in the
construction industry are damp-proofing and
waterproofing,” said Joseph Vaccarella, senior
vice president of Cosella-Dorken Products Inc.
(http://www.deltams.com/ ), manufacturers of
DELTA-MS and DELTA DRAIN air gap mem-
brane waterproofing products, based in Beams-
ville, Ontario, Canada. “Let’s take a look at what
these two terms actually mean and how the
systems related to each of the terms really work
to protect the foundation of homes and almost
every other structure that has a foundation,”
Vaccarella said.
Damp-proofing
“Most building codes describe damp-proofing
membranes to be a preparation (coating) that
is applied to the exterior surface of foundation
walls in areas that are not expected to be sub-
ject to hydrostatic pressures due to soil mois-
ture conditions and act to separate usable living
space from exterior below ground conditions.
These preparations act as capillary breaks to
stop the movement (migration) of liquid moisture
in the soils from coming into direct contact with
the exterior face of the foundation wall system.”
Damp-proofing materials are almost always oil-
based and the majority are still in liquid form
applied by a spraying or rolling method. There
is normally no special detailing required when
applying these materials because hydrostatic
pressures are not a factor in the coatings
ability to perform a capillary breaking function.
In addition, the use of damp-proofing is (contin-
gent) relying on the installation of an adequate
foundation perimeter drainage system to assist
in controlling any build up of water that might
occur in the local soils.
Low permeance
Damp-proofing materials normally have a
relatively low permeance value (ability to resist
migration of moisture in soils from penetrating
the coating), except in the case of polyethylene,
which has a very low permeance value. A per-
meance (or perm) value is defined as a measure
of how quickly water/vapor diffuses through a
material, with a vapor retarder (barrier) being
defined as a material having a permeance value
of 1.0 or lower.
“One of the determining factors affecting the
performance of damp-proofing coatings that
are spray applied is an issue of quality control.
Most of the manufacturer’s stipulate that their
product meets a particular perm rating pro-
vided that the material is applied to a specific
thickness for the application. The application in
terms of thickness is generally measured in mils
and most finished coatings are in the range of
30 mils to 60 mils wet application with a dry film
thickness after curing of 15 mils and up.
Waterproofing
Most building codes describe waterproofing
membranes to be a preparation (coating/bar-
rier) that is applied to the exterior surface of
the foundation walls in areas that are known
or are expected to be subject to hydrostatic
pressures due to soil moistures conditions.
Like damp-proofing, it separates usable living
space in basements from exterior below ground
conditions.
“These membranes act not only as capil-
lary breaks to stop moisture contact with the
foundation wall, but also provide protection for
the foundation from the effects of hydrostatic
(water) pressure build up around the founda-
tion from being forced into direct contact with
the foundation wall under a hydrostatic head of
water, which can leads to major moisture prob-
lems for you and your basement.”
Experience has shown that failure of waterproof-
ing systems is the result of improper installation
and material incompatibilities. This originates
from a lack of understanding on the part of the
installer to know that application procedure prior
to starting the job, in addition to using substitute
materials without input from the designer.
Most waterproofing systems employed for foun-
dation protection use some form of drainage/
protection layer in front of the waterproofing so
the main component is not damaged during the
backfilling operation, and reduces the potential
for water to penetrate the waterproofing mem-
brane. In almost all cases the installation of a
waterproofing system on a foundation wall will
perform the functions of damp-proofing and
waterproofing at the same time because of its
enhanced features. Installation of waterproof-
ing in areas that are not normally expected to
be subject to hydrostatic pressures due to soil
moisture is permissible; however, while the cost
for this type of installation under these circum-
stances is a little excessive, it gives the end user
some added peace of mind should he ever need
the extra protection.
Choosing the right type of foundation protection
for your situation requires careful planning and
choices that must be considered. Do the proper
investigation before hiring an architect or speci-
fier to draw your plans. You can obtain some of
Damp-proofing or Waterproofing
By Christopher Brooks
continued on page 39
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Photo courtesy of Cosella-Dorken