Concrete slabs: What are the proper methods for conducting moisture tests? By Pete Robitaille
A problem, a curse, a nightmare… These are just a few of the
until a natural balance is reached. Moisture problems may ei-
terms that flooring professionals use to describe moisture-
ther present themselves soon after the flooring installation is
related flooring failures. The outcome is usually the same,
complete, or down the road, at any time during the lifetime of
whether the source of moisture comes from the concrete slab
the building due to climactic or environmental changes. For
itself, or stems from drainage issues; burst pipes; condensa-
this reason, it is imperative that all concrete slabs, old or new,
tion; aggregate above a membrane; or upward migration from
be tested for moisture vapour emissions.
the ground. The contractor receives the dreaded callback from
Moisture test results are considered to be highly valid for
the building owner or maintenance facility manager, wonder-
installations involving vapour barriers. For those installations
ing why the finish layer is a mess, and the contractor’s night-
that do not use vapour barriers, moisture vapour test results
mare begins.
provide only a snapshot perspective (i.e., they are only valid
Fortunately, today’s construction industry offers well-re-
for that moment in time). Moisture will continue to be emitted
searched test equipment and methods for measuring con-
from one day to the next, from season to season, and year to
crete slab moisture which substantially reduce the risk of floor-
year – creating an unpredictable outcome for a future flooring
ing failure, starting at the subfloor’s surface preparation stage.
installation. The second most common source of moisture is the result
Common sources of moisture in slabs
of capillary action in a new concrete slab. A slab is typically laid
One of the most common sources of moisture in concrete is
in accordance with the building code that specifies use of a
the ground, via capillary action or hydrostatic pressure beneath
vapour barrier directly below or in a steel base. Any moisture
a slab that is not properly protected by a suitable moisture
in the slab is due to residual humidity, which is expected to dis-
vapour barrier. The concrete slab acts like a sponge, drawing
sipate in time. The amount of time this would take depends on
moisture upward from damp areas below toward the surface,
many factors: climatic and environmental conditions that occur
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Ops Talk • Spring 2013
