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Ground Stability, Foundations and Substructures 147
through joints provided they are solidly cast up to or inside sound concrete and there is
no gross contraction at construction joints or movement at expansion joints.
Tanking
The term tanking is used to describe a continuous waterproof lining to the walls and floors
of substructures to act as a tank to exclude water.
Mastic asphalt
The traditional material for tanking is mastic asphalt, which is applied and spread hot in
three coats to a thickness of 20 mm for vertical and 30 mm for horizontal work. Joints
between each layer of asphalt in each coat should be staggered at least 75 mm for vertical
and 150 mm for horizontal work with the joints in succeeding coats. Angles are reinforced
with a two-coat fillet of asphalt. Asphalt tanking should be applied to the outside face of
structural walls and under structural floors so that the walls and floors provide resistance
against water pressure on the asphalt and the asphalt keeps water from the structure. Figure
3.68 is an illustration of asphalt tanking applied externally to the reinforced concrete walls
and floor of a substructure or basement. The horizontal asphalt is spread in three coats on
the concrete base and over pile caps and extended 150 mm outside of the junction of the
horizontal and vertical asphalt and the angle fillet. The horizontal asphalt is then covered
with a protective screed of cement and sand 50 mm thick. The reinforced concrete floor
should be cast on the protective screed as soon as possible to act as a loading coat against
water pressure under the asphalt below.
Pavement
Protective screed on
two coat asphalt
Concrete floor
Half brick wall
Space flushed
with mortar
Three coat
mastic asphalt
Two-coat angle
fillet
Reinforced concrete roof
Reinforced
concrete wall
Reinforced concrete floor
on protective screed
Three-coat asphalt
Concrete beam
Concrete
column
Concrete beam
between pile caps
Concrete base for
asphalt
Reinforced concrete
pile cap
Piles
Angle
fillet
Three-coat
asphalt
Figure 3.68 Mastic asphalt tanking.