Whether multi-storey, underground
or over an occupied space, car
parks can be difficult to both build
and maintain. Vulnerable to attack
from water, chemicals, chlorides
and UV radiation, they are also exposed to
de-icing salts and exhaust fumes that can further
accelerate the deterioration process.
Failed deck joints and surface waterproofing
can cause severe maintenance problems and
lead to surface water leaking to the decks
below. This in turn, causes corrosion of the steel
reinforcement and compromises the integrity of
To help overcome these challenges, liquid
applied waterproofing systems are regularly
specified for car parks as they provide a tough,
elastomeric, seamless and decorative finish.
Furthermore, the speed of application and
quick curing times are essential benefits when
refurbishing structures which have to remain
partially open to the public.
To help contractors who are responsible
for waterproofing cark parks, the LRWA has
produced a Code of Practice which shares best
practice and knowledge:
Prior to specifying a liquid applied waterproofing
system, contractors should carry out a full
inspection of the structure to establish the most
appropriate product and to check for any remedial
work required as well as potential issues.
Car parks can be constructed using several
different techniques, some of which can
increase the risk of issues such as movement
and deflection, so understanding how it has been
built is essential.
An inspection should take into account
the condition of the supports, structural
decks, parapets and safety barriers, existing
waterproofing, any expansion joints and the
If any deck can’t be inspected from below, core
samples should be taken from the external surface
through to the deck to assess the condition.
To enable the liquid waterproofing system to
be installed effectively, there must be a suitable
Vehicles braking and accelerating on a
surface exert a considerable amount of force on
the waterproofing system. It is therefore essential
that there is good adhesion and cohesive strength
within the surface of the substrate.
Surface coating treatments should only be
carried out on substrates that are structurally
072 JUNE 2018 RCIMAG.COM
Waterproofing car parks:
advice and best practice
This month, Sarah Spink, chief executive of the Liquid Roofing and Waterproofing Association (LRWA), discusses
the challenges of waterproofing car parks and offers guidance from the association’s Code of Practice
The Grand Arcade car park in Cambridge recently had a liquid applied waterproofing system specified
sound. Care should be taken to ensure that the
application of a new decorative coating is not
masking a deterioration problem within the
substrate that could go undetected.
For construction of new car parks, the surface
finish should be specified by the manufacturer of
the liquid waterproofng system to minimise the
need for additional surface preparation.
Unformed concrete surface finishes can
be placed, finished and cured in a variety
of ways that can significantly affect surface
strength, regularity and texture. The concrete
specification can define the method used to
finish the concrete and achieve the surface
Asphalt substrates will generally be found on
existing car parks where the client requires a
new liquid waterproofing system. Overlaying
the existing asphalt surface can reduce
disruption, save costs and minimise loss of
revenue for the client.
There are three main types of hot asphalt:
hot rolled asphalt, asphalt concrete, and mastic
asphalt, which is used for waterproofing and
wearing courses on trafficked decks.
Mastic asphalt has historically been
most widely used on car park decks. When
considering if this is suitable for an overlay,
consider the possibility that some water or
moisture may be trapped between the asphalt
and the structural deck beneath. Typically, if
this is the case, the asphalt will already show
significant signs of blistering.
Preparing the roof
Before applying the liquid waterproofing
system, the substrate must be clean,
uncontaminated and stable.
When cleaning, it is important to ensure that
debris doesn’t block the rain down pipes and
other drainage. Drainage gullies are commonly
found on parking decks, so they should be
plugged before preparation works begin to
Rainwater gullies should, where possible,
be prepared into the throat of the drainage pipe
so that the liquid waterproofing system can be
continued well into the gully detail to ensure a
watertight seal in this vulnerable area.
Metal flashings should be lifted or removed
to allow the system to be installed on upstands.
Flashings should then be replaced if required
or alternatively the manufacturer should
recommend a suitable detail which may avoid the
need to replace the flashings.
Where an existing chase is present in the
upstand, any existing filler should be removed
to allow the membrane to be dressed in.
The chase should then be re-pointed with a
suitable mastic/filler in accordance with the
It is common to carry out repairs and preparation
work on a phased basis in live car parks, and it is
therefore extremely important to consider traffic
management and the safety of the general public.
These considerations should be covered in health
and safety method statements.
Contractors should make the client aware
of cure periods during which the liquid
waterproofing area must not be trafficked either
by the public or vehicles. Access should be
prohibited with suitable traffic and pedestrian
Prior to opening up the area, contractors
should carry out a joint inspection with the client
to sign off the deck ready for trafficking.