REGULARS: ROOFING MATTERS
Waterproofing 101…
Once the rainy season subsides it is always a clever idea for property
owners to turn their attention to waterproofing their roofs.
By Phil Llewellyn, chairman of the Damp-proofing and Waterproofing Association of Southern Africa (DWASA)
H
For the past 30 years or more, flat-roofed
buildings have been waterproofed using
bitumen torch-on membrane. This is a
fabric reinforced bitumen roll that is heat-
fused to the roof surface using a gas torch.
Provided that the bitumen membrane is
omeowners on the Highveld
should waterproof their roofs in
winter and those living in the Cape
should do it during the summer.
Leaks on pitched, tiled roofs are mainly
due to cracks or misalignment of tiles and
roof capping and possibly even the flashing
that joins the tiles to side walls. These can
usually be fixed with a minimum of effort
and expense.
According to SANS 10400 – all roofs with
pitch of less than 26 degrees or more than
45 degrees, and all roofs in coastal areas
(up to 30km from the sea) should lay an
under-tile membrane that is loose-laid so
that water can drain between the rafters. If
an under- tile membrane is properly laid it
will provide a very effective, impermeable
barrier against wind-driven rain and dust.
For this reason, the SANS 10400 also states
that underlays should be provided for all
slate and tiled roofs, no matter what the
pitch (or slope) and where ceilings are
not installed.
Flat roofs, on the other hand, represent
a different challenge.
The types of products available to
waterproof a roof slab are varied and
increase in number and type every year.
The following waterproofing products
are currently in use in South Africa; some
are a more recent vintage:
• Bitumen torch-on membrane
• Cementitious systems
• Polyurethanes
• Polyurea
• Acrylics
• PVC products
• Crystalline products
Different products are available for waterproofing different kinds of roofs.
properly fused to the surface and all
overlapping rolls are properly sealed there
should be no problems, always if all outlets
and any extrusions on the surface of the
roof, such as air-conditioning fittings and
satellite dishes, are also suitably sealed.
The rolls come in a few thicknesses usually
3.4 and 5mm and may or may not be plain
in finish or with a mineral chip covering.
The former requires regular coatings of
bitumen aluminium paint to provide
ultraviolet (UV) protection to the membrane
while the latter requires no further UV
protection and come in a variety of assorted
colours. Owing to their large carbon
footprint, the use of an open flame during
application and the non-degradable nature
of the product, torch-on membrane is being
phased out in Europe and will in time
probably experience the same fate here
in South Africa.
Cementitious systems are commonly
used to protect properties against lateral
damp but are not widely used to waterproof
roofs. Since cement-based products crack
with any slight movement they are best
used in conjunction with a polypropylene
membrane and certainly not on roofs
greater than 40m 2 . Application is simple,
and the product can be applied to a damp
surface but not to a wet one.
Polyurethane waterproofing products
are relatively new to South Africa but have
been used in countries worldwide for the
past 30 years. They have high flexibility, are
resistant to mechanical and thermal shock,
are UV stable and resistant and fairly simple
and quick to apply. Once cured they are
maintenance free. There are a range of
products covering applications from roofs
to parking decks to water tanks to flooring
and swimming pools. They are simpler and
quicker to apply than most other
waterproofing products and if damage
occurs they are simple to fix.
Product variety
Polyurea products are usually associated
with large roofing and parking deck areas.
They require sophisticated spraying
equipment and highly skilled operatives
and are mostly suited to large shopping
malls and industrial properties.
Acrylic products are not suitable for flat
roof areas. While they are simple to use and
apply, they do require regular maintenance
See more on page 26
24
JUNE 2018
RESIDENTIAL // COMMERCIAL // INDUSTRIAL