How does one convert a dull bitumen-coated flat roof or terrace into an attractive paved surface without the use of grout or any other form of binding agent? One answer is to be found in suspended paving, a process which uses concrete flagstone pavers without the use of any binding agent.
Unlike conventional paving or tiling on a concrete surface in which the pavers or tiles are attached directly onto a concrete base layer using grout or some other binding agent to create an impervious watertight surface, in suspended paving the pavers are mounted on small polythene sandbags (see picture) without the use of any adhesive or binding agent. All that is needed to keep the pavers firmly in place is their weight. Moreover, they are laid 10-12mm apart which creates a water permeable surface.
These and other advantages are why suspended paving is finding increasing favour among some of the country’s leading architectural practices. And the process has already been used on some major construction projects using pavers supplied by Cape-based Concrete Manufacturers Association NPC (CMA) member, Revelstone. Recent projects include: Cape Peninsula-based projects such as Liberty Life’s headquarter premises in Century City; Bloemhof in Tyger Valley; Wembley Square in Gardens; and some student residences in Stellenbosch. Suspended paving has also been used at Dainfern Square in Johannesburg and Liberty Life’s Umhlanga offices in KwaZulu-Natal, among other high-profile projects.
According to Johnny Schwartz, a partner of Louis Karol Architects – a suspended-paving pioneer – the process offers some distinct advantages over conventional roof-top or terrace paving.
“In the first instance it allows for the creation of a level paved surface on a base which is sloped for drainage purposes. Flat surfaces are achieved by altering the thickness of the supporting sandbags to compensate for the slope. Secondly, because the paved surface is permeable, there is no water pooling even during the heaviest of storms. This means that as soon as the rain has abated, the surface can be walked on without any concerns for wet feet.
“Another major advantage is the fact that the paved surface creates a protective layer which shields the waterproofing on the base layer from the sun’s UV rays and from other forms of possible damage. However, in the event that the base layer does require some routine or other maintenance work, it is easily effected by simply lifting the pavers and then re-inserting them once the job is completed.
“Contrast this with the expense and inconvenience of lifting and replacing pavers which have been grouted to the base layer. Moreover, no expansion joints are needed with suspended paving and there is no chance that the pavers will crack or lift due to wind or earth-induced movement,” says Schwartz.
Revelstone director, Alex Cyprianos, says that suspended paving is generally used in low-traffic areas such as concrete roofs, balconies and terraces.
“The pavers tend to be large, averaging 600mm² and 55mm thick. We produce a wet-cast flagstone paver for the purpose which is steel reinforced, and we can also make up special shapes to accommodate curved borders.”
The sandbags used in suspended paving are filled with a mixture of sand and cement which hardens once the laying process has been completed. Over time the polythene outer casing will deteriorate leaving a hard and durable concrete core.