The lowering of standards in the construction industry has been under the spotlight for over five years; and for good reason. Failures, some of them major and incurring injury and loss of life, have led to huge wastage in human and material resources. It is a dangerous development which is alarming to reputable manufacturers and construction-related institutions.
An example of what happens when standards are side-stepped to win contracts, the floor screeds of a large mixed-use retail and residential development in Johannesburg’s CBD have cracked extensively.
The main contractor had excluded steel mesh, an essential component when placing screeds on precast flooring, as the precast supplier had misled him, saying that his slabs did not need mesh in the screed.
The main contractor has now been replaced and a painstaking process of removing the flawed screeds and replacing them using approved building practice has begun. Apart from the cost of replacing these screeds, the completion of the whole development has been delayed by several months, resulting in a loss of rental income.
Commenting on this incident and the flaunting of standards in general, Bryan Perrie, MD of The Concrete Institute (TCI), says: “There is a price to pay and often it’s the client who pays it, as proving culpability is an expensive, time-consuming and often fruitless exercise. Therefore, getting it right the first time using tried and trusted standards and specifications endorsed by institutions such as TCI, the CMA (Concrete Manufacturers Association), the NHBRC, the CSIR, and SABS, is in everyone’s interest. Industry professionals like architects, quantity surveyors and civil engineers should insist that proper specifications are followed.
“Nonetheless, as this screed failure amply demonstrates, contributions made by professionals are sometimes found wanting. It is thus important for property developers to become acquainted with building standards and specifications and insist on their implementation. Alternatively, they should see to it that the professionals they employ will do so. If not, they are behaving irresponsibly, both to themselves and their prospective tenants,” says Perrie.
These views are supported by Echo Prestress, South Africa’s largest manufacturer of precast hollow-core slabs and a member of the CMA.
Echo sales and marketing director, Melinda Louw, says any hollow-core or beam and block precast slab supplier who claims that mesh is not a requirement when pouring screeds on floor slabs, especially in exposed areas such as balconies, walkways, roofs and tiled areas, is being deliberately misleading.
“The construction industry in general and contractors in particularly should be extremely wary of such claims which ultimately sully the reputation of the whole precast slab industry. We therefore encourage any user to contact us about any aspect on the proper installation of precast flooring, especially when confronted with performance claims which appear to flout good building practice. Our screeding procedures, which include details on screeds for balconies, roofs, walkways and car parks, is available free and offers sound technical advice. Moreover, more detailed and technical screed information is available from TCI which has published a brochure entitled Sand-cement screeds and concrete toppings for floors. Screeds are also covered in a National Standard SANS 10109-2.
In most instances, especially when Echo Prestress flooring slabs are used, a simple 40-mm levelling screed is all that is required. However, in buildings with large floor areas, movement jointing should be specified by a consulting engineer to avoid cracking.
Anyone interested in obtaining the screeding procedures leaflet from Echo Prestress should contact André Combrink on +27(0)11 589 8800. For copies of TCI’s screeding brochure, call +27(0)11 315 0300 or download it off www.theconcreteinstitute.org.za .
