Plumbing Connection Winter 2022

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2 6 PLUMBING CONNECTION Winter 2022
A. The use of a ‘clay plug’ in the trench
(See Diagram 1) directly under the
edge of the slab to prevent ingress of
water, rather than filling with sand or
gravel. For example, Images 1–3 show
the installation of the Plastec clay
plug and the section of the trench,
showing how the clay plug prevents
the ingress of water.
B. The use of a second swivel/knuckle
joint where pipework exits the slab for
H1, H2 and E class soil. (See Diagram
2.) Whilst one swivel provides angular
DIAGRAM 3 DIAGRAM 4
deflection the second swivel works in
partnership providing full articulation.
Think of your wrist and elbow working
in conjunction. This crucial part of
the drainage system, where pipework
moves from dry stable ground under
the slab into ground affected by
moisture, is where the most common
damage is found.
C. The installation of expander
joints on all vertical risers entering
the soil for class H1 and H2 sites.
For E class sites the Appendix not
only protects against upwards heave
and downwards settlement with
expander joints it also safeguards
sideway deflective stress with
a swivel or knuckle joints. (See
Diagrams 3 and 4.)
Some might argue that this is an
extreme solution, but with many E
class soils moving in excess of 150
mm when laden with moisture, it’s
an extreme solution to an extreme
problem. The need for expansion on
vertical risers beneath the slab does
add height to the drain and requires
forethought and planning from the
plumber. Images 4–5 show photos of
correct configurations.
Fortunately, there are products
available which allow plumbers to
meet these requirements and Plastec
is happy to offer design support to
assist with this topic. Chris Ferguson
is the product specialist and provides
regular lectures on the topic around the
country.
Additional information can be found at
urn:li:activity:6854637143801888768
Visit for more
information. Images 4–5. Vertical risers in correct configuration.
UNSTABLE SOILS- CHRIS FERGUSON & DR GREG MORWOOD
Use expander joints on all vertical risers entering the soil for class H1 and H2 sites.