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SIG D&T ProTwenty Solves 50-Year-Old Problem For Financial Services Organisation 

Persistent failure over the last two decades of a roof housing one of the world’s leading financial institutions has finally been resolved thanks to one of SIG Design & Technology’s most advanced membranes.

The 950sqm flat roof of the business’s Burgess Hill office in West Sussex, has been re-roofed with various waterproofing systems numerous times since the four-storey office block was built in the 1960s. Each time the application has failed to keep the building watertight and a new solution has been sought.

Now, the financial services company has experience of the results, performance and 15/20-year warranty of the ProTwenty re-roof, it is looking to use the membrane on other buildings in an extensive UK property portfolio.

The Burgess Hill office has certainly put Pro-Twenty through its paces. The choice of membrane had to be robust, safe and flexible enough to cope with numerous obstacles and a variety of end uses.

The flat roof area of the commercial building doubles up as a canteen patio and one of the building’s main fire escape routes. The 950sqm area is dotted with pillars supporting an upper storey, as well as the usual building service protrusions found on flat roofs. The application of the membrane also had to take into account the building’s cladding and glass frontages.

The FSO required uninterrupted use of the building and the company, quite rightly, practises exacting health and safety standards. With hot-flame application of roofing membranes known to have started the occasional office fire, this was a risk (however minimal) that would not be countenanced by the company’s maintenance team. If a hot-flame application had been specified, the building’s fresh air intake would have been polluted and a health hazard caused for the occupants of the building.

This demanding combination of factors made the choice of membrane obvious for Canterbury-based contractors, The Flat Roof Recovery Company.

As an inherently flexible polyester-reinforced liquid application, ProTwenty provided the perfect flame-free (and therefore risk-free) solution to the Burgess Hill office block’s 50-year-old roof water ingress problem.

No flame involved in application, the membrane is painted on by roller in three stages, with polyester embedded into the system while wet: effectively creating a continuous single-ply roofing system in-situ.

It brought to the job all the benefits of liquid waterproofing – a membrane which could be applied easily and smoothly around the building’s pillars, protrusions and cladding, which are the points most likely to fail where single-ply membranes are utilised.

And Pro-Twenty brought the strength and resistance of single-ply. Usually, unreinforced liquid waterproofing systems depend on elasticity to cope with inevitable building movement.

In the case of 1960s concrete monoliths, building movement is particularly pronounced and therefore problematic for membrane adhesion. Concrete continues to cure over 50 years and can becomes brittle after that time: wear and tear, building modifications and all sorts of movement cause cracks. The sheer force of the movement of the substrate will cause a non-reinforced liquid waterproofing membrane to fail.

As ProTwenty is reinforced with polyester, rather than plasticizers(glass fibres), the membrane can account for the force of building movement. The reinforcement relieves the tension created by substrate movement, which means ProTwenty is much more robust.

The final UV protection coat prevents the membrane being degraded by harsh sunlight, further enhancing its durability. The membrane confidently outperforms its lifetime warranty of 15/20 years, which itself is extendable in five-year increments and indefinitely after the initial warranty period. ProTwenty therefore provides a waterproofing solution for the lifetime of the building.

The membrane may be a relative newcomer to the UK (it was introduced in 2003) but its waterproofing and durability have been tested by conditions which far outstrip anything the British weather, however unpredictable, can throw at a building.

Pro Twenty was developed in South Africa in the 1970s by eminent chemist Rob Kaufmann and has since been used widely across Australasia, South Africa, the Middle East, Germany, India, Canada, USA and South America, coping with these countries’ extreme weather conditions.

Its liquid application makes it versatile too. In the case of Burgess Hill, the membrane was applied in two different colours to delineate separate sections of the roof. Most of the membrane was applied in grey but green was applied to a long section around the perimeter to delineate a fire escape walkway.

With it being a safety route, the walkway had to have non-slip properties. The requirement was achieved by using a ProTwenty Wear Coat with added kiln dried sand to increase its slip resistance. The Wear Coat in turn was framed in white ProTwenty to highlight it being a delineated walkway.

And with the building’s canteen opening out onto the roof, a section was tiled using glass-reinforced concrete (GRC) tiles. The tiles were applied directly onto the ProTwenty membrane, further demonstrating its flexibility in application.

The entire membrane was applied directly on top of the existing faulty membranes. Cracks and defects were made good and ProTwenty was applied over the top.

The job was completed within just eight weeks, without interruption to the client’s day-to-day activities. A perfect finish to a 50-year-old issue.


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Arundel Jones Associates Ltd Registered in England and Wales No. 07334149
Hill Farm, Linton Hill, Maidstone, Kent ME 17 4AL
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