REGULARS: ROOFING MATTERS
Waterproofing
“ a roof
is not
something that
should be tackled
on a DIY basis.”
The types of products available to waterproof a roof slab are varied and increase in number
and type every year.
Maintaining the proof
So much for the theory. Most roofs leak
due to either poor design, poor application
of a product or failure to maintain
the product.
Flat roofs need to be designed with a
minimum fall of 1:50 to sufficient numbers
of proper-sized outlets to handle the
volume of water experienced during a
rainstorm. Such outlets need to be of at
least 100mm in diameter. As an example, a
100m 2 roof in a 2.5cm downpour will
generate about 3 000ℓ of water. Imagine
that trying to push its way through just one
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JUNE 2018
RESIDENTIAL // COMMERCIAL // INDUSTRIAL
50mm outlet! In recent months some of
our storms have generated as much as
6mm within a matter of minutes. So, size
and number of outlets are important as
well as keeping them free of debris. They
also need to be fitted at the height of the
floor slab and not above it otherwise water
will ‘pond’ for a considerable amount of
time before any runs off.
Gutters and downpipes need to be
cleaned of all debris and any rust in metal
gutters dealt with before coating in an
acrylic, polyurethane or even rubberised
bitumen to prevent further deterioration.
Joints in waterproofing need to be
inspected and repaired as necessary and
torch-on membrane checked for an
effective UV coating. If necessary two coats
of bitumen aluminium paint should
be re-applied.
What sums it up
However, the last point is professionalism.
Waterproofing a roof is not something that
should be tackled on a DIY basis nor
should the responsibility be given to
any-fly-by-night-body. The company
selected to do the work should have at
least a three-year track record, should be
using products that have been tested by a
reputable testing authority that are
properly guaranteed. They should also give
their own workmanship guarantees and
ideally belong to a professional industry
association. ‘Penny wise, pound foolish’ is
unfortunately a sound maxim as often the
cheapest quotation is the one that costs
you more than twice as much in the
long run.
and rely on a sloped surface to ensure
regular run-off of water. Should ‘ponding’
of water occur, due to a lack of run-off to
the roof outlets, the acrylic will re-emulsify
resulting in degradation of the product and
eventual water ingress. Acrylic products
are commonly used to waterproof tops of
parapet walls and flashings.
Polyvinyl chloride (PVC) products are
also relatively new to South Africa. Sheets
of PVC are laid on to polypropylene and
then hot-air welded together. There is,
therefore, no direct bond to the underlying
roof surface. The products are UV and fire
resistant with good solar reflectivity and
are suitable for all types of application.
They are relatively simple to use and apply.
Crystalline systems rely on special
additives mixed with new concrete to form
insoluble crystals within the concrete,
effectively blocking the pores. Such
products are obviously best used when
laying a new concrete slab, usually during
construction or renovation.
Phil Llewellyn, chairman of DWASA.
ABOUT PHIL LLEWELLYN
He is the co-owner and director of
Safeguard Chemicals South Africa and
Maris Polymers South Africa. Both
companies specialise in products for the
damp-proofing and waterproofing
industry. Chairman of DWASA since
January 2016, he is passionate about
training and the need to uplift the
standards of knowledge and skills
within the industry. At 73 he is still very
active both within the businesses and in
his social life and hopes to pass on his
knowledge and passion to others who
will embrace his vision for the industry.