Page 234 - Masonry and Concrete

Footings, Foundation Walls, Basements, and Slabs
233
FOOTINGS, FOUNDATION WALLS, BASEMENTS, AND SLABS

particularly important when reinforcing steel may be corroded by pro-
longed moisture exposure or chloride contamination from the soil.
Negative side waterproofing is generally used only as a remedial mea-
sure in existing buildings where outside excavation and repair are
impossible or prohibitively expensive.
Since a waterproofing membrane must withstand hydrostatic pres-
sure, it is critical that all holes, cracks, and openings in the wall be elim-
inated. This is easier to do below grade than it is in above-grade walls
because of the absence of doors and windows, because there are fewer
joints, because thermal expansion and contraction is less with smaller
temperature variations, and because there is no ultraviolet deterioration
of materials. Perfect barriers, however, are still difficult to achieve, and
the barrier concept is very unforgiving of application errors. When com-
bined with effective subsurface drainage, however, a waterproofing
membrane can provide good performance even though human error
will inevitably introduce minor flaws into the system. In wet climates,
or on sites with high water tables, fluctuating water tables, or poor
drainage, a waterproofing membrane should be used in addition to sub-
surface drains, free-draining backfill, or drainage mats.

REPAIR CRACKS WITH
CEMENTITIOUS GROUT

TOPPING
SLAB

a. POSITIVE SIDE WATERPROOFING b. NEGATIVE SIDE WATERPROOFING
FIGURE 6-40
Positive side and negative side waterproofing. (from Beall, Christine, Thermal and Moisture Protection Man-
ual, McGraw-Hill, New York).

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