SPECIAL FEATURE:
KIWI MOSTPOERCISAPL OFERATTURE: CORROSION CONTROL AND COATINGS
Figure 5 – Lower polyurethane coating peeling away from surface
while upper epoxy blisters due to bubbles in application.
The Calcium Aluminate Cement coating in Figure 6 has come to the
end of the life, having been consumed by the acid within this rising main
discharge manhole.
36 June 2018
Figure 8 – Magnesium Hydroxide showing discolouration
(left) and cracking (right)
Figure 8 shows a Magnesium Hydroxide coating
that was fully intact and neutralising the acid,
but had been discoloured by a nearby gum tree
releasing tannins into the stormwater, which resulted
in streaks down the hole.
If standard commodity grade Magnesium Hydroxide
is used or an appropriate procedure coating
application is not followed, coatings can result in the
material not adhering to the surface or cracking and
falling off the concrete surface.
Figure 7 – Magnesium Hydroxide Coating taken off by storm
water coming through lid.
Figure 6 - Calcium Aluminate Cement consumed by strong
acid attack
Magnesium Hydroxide coatings can suffer from early life failure if the
product quality and application process are not adhered to. The photos
in Figure 7 show the issues that can be faced if the manhole lid is not
sealed to prevent water ingress through the lid.