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Ground Stability, Foundations and Substructures 149
1
Pipe coated with
sleeve of asphalt
2
Pipe through hole in
wall
3
Asphalt applied to
wall and joined to
sleeve
Basement
wall
4
Wall built
against
asphalt
Figure 3.70 Four stages in forming asphalt collar around pipe.
on the asphalt. Internal asphalt is sometimes used where a substructure to an existing
building is to be waterproofed.
Service pipes for water, gas and electricity and drain connections that are run through
the walls of a substructure that is lined with asphalt tanking are run through a sleeve that
provides a watertight seal to the perforation of the asphalt tanking and allows for some
movement between the service pipe or drain and the sleeve. The sleeve is coated with
asphalt that is joined to the vertical asphalt with a collar of asphalt, which runs around the
sleeve, as illustrated in Figure 3.70.
Asphalt that is sandwiched in floors as tanking has adequate compressive strength to
sustain the loads normal to buildings. The disadvantages of asphalt are that asphalting is a
comparatively expensive labour-intensive operation and that asphalt is a brittle material
that will readily crack and let in water if there is differential settlement or appreciable
movements of the substructure. In general, the use of asphalt tanking is limited to substructures
with a length or width of not more than about 7.5 m to minimise the possibility
of settlement or movement cracks fracturing the asphalt.
Bituminous membranes
As an alternative to asphalt, bituminous membranes are commonly used for waterproofing
and tanking to substructures. The membrane is supplied as a sheet of polythene or polyester