Annemerie Hilhorst, MD, Twinstar

Q: What are the benefits of polymer?
A: Also known as polyester resin, or fibre resin, polymers are created from liquids mixed with styrene, which – with the inclusion of other additives – makes them flexible enough to be moulded. It’s a composite that is versatile and light without compromising strength, and can be coloured for different applications and identification.

Q: What industries have the biggest need for precast and polymer components?
A: The bulk of our clients are in the civil infrastructure industry – largely roads, stormwater, electrical and water reticulation. We’ve also spread into the telecoms infrastructure space with the provision of manhole covers, which is something we’ve been producing for municipalities for some time now.

Q: What are the challenges of cast-iron manhole covers, and how do they compare to polymer versions?
A: Using polymer is an excellent replacement for cast iron for different reasons. Firstly there is a proliferation of metal thieves in SA, and their theft of cast-iron manholes have caused tremendous problems for municipalities – not just from a cost perspective but because of the safety risk to pedestrians and damage to vehicles. The financial loss across the nation has been in the millions of rands.

Replacing cast-iron or ductile-iron manhole covers and their frames with a polymer version is a solution because they have no significant resale value; are able to withstand the same strengths; and can be up to 30% cheaper.

Q: What has driven the need for custom-made polymer and precast products?
A: The civil infrastructure environment has transformed enormously because there is a broader thinking about the utilisation of space, cost factors, aesthetics and in creating something unique. With this brings challenges for quality surveyors and project managers who have been known to cast products on-site because a standard product did not fit, or they sought a solution to a problem.

This situation isn’t ideal, especially if the solution applies to a limited quantity. And given that the concrete precast industry is focused on mass production, it’s not cost-effective for the companies supplying such products to stop a production line for non-standard or once-off items.

Precast concrete and polymer products are particularly useful because builders no longer have to contend with off-the-shelf products. Instead they can commission a fit-for-purpose design, have a mould made and order in single or limited quantities, or in bulk. In being able to manufacture a specialised solution to specification, we can produce pretty much anything – if it is possible to mould – from a few kilograms up to 6 tons. Twinstar has even produced floating stairs with a recess for LED lighting, and down-chutes behind gutter pipes on an office building as a feature.

Q: The renewable energy market appears to have a big need for precast and polymer components. Is this correct?
A: We’ve been supplying precast concrete plinths for wind-farm transformers over the past four years, as well as precast combiner boxes and distribution boxes for cable connections. The plinths weigh 6 tons and require an oil containment area for drainage, repairs and fittings to enable client access, particularly when there is a need to pump out fluid from the units.

The units we supply are manufactured using a combination of concrete and polymer; the main structure being produced from concrete and lockable lids from polymer. And because polymer is so versatile, we have also been able to embed the international danger sign for electricity and other such warnings, onto these lids.

Q: Do you often interact with designers?
A: It is rare for specialists of custom-made products to be consulted at the design stage. Architects design what they would like to see installed; it is up to the builder to find the products to meet specifications. On the odd occasion when a particular design is challenging (for example, a certain thinness may be required), we do interact with the architect to find an alternative as close as possible to the original design that is practical for us to cast but still be approved for quality.

Q: What is the turnaround time in terms of manufacturing a specified product?
A: As we make non-standard products, we do not keep stock. All customer needs are quoted and produced on order. Small quantities and once-off items are usually produced within two days of the order, depending on the quantity, and the quality is tested daily by casting test tubes. This is undertaken by an independent laboratory.

By Kerry Dimmer
Illustration: Janine Petzer

Article written by