Mastic asphalt is often perceived as the traditional choice of specifiers due to its long and illustrious history as a roof waterproofing medium.
A material that can boast a history dating back to the Phoenicians, the product was patented by Mr Claridge in Paris in 1837 and mastic asphalt became known as Claridge’s Patent Asphalt. Successfully used to provide exceptional protection from water penetration for centuries, mastic asphalt has maintained its place as the waterproofing material of choice throughout the centuries and is still specified today for many of the UK’s most prestigious buildings from St Paul’s Cathedral to Buckingham Palace.
Nevertheless, mastic asphalt has also evolved with the needs of modern construction and has taken on a number of modern guises. Traditionally, mastic asphalt comprises of limestone aggregates bound together with bitumen. In more recent years, mastic asphalt manufacturers have rejuvenated the material with the incorporation of advanced polymer modified formulations to ensure all the performance characteristics of traditional asphalt systems, with the added benefits of increased flexibility, enhanced handling and sustainability. Combining its traditional strengths with modern technology.
Mastic asphalt is often specified due its durability with a life expectancy of 50 years or more. Its robust nature ensures it can withstand extreme weather conditions and attack from thermal shock which is a frequent source of breakdown in many other types of membrane. Roofs in the UK are exposed to the elements and temperatures ranging from 38?C. in summer, all the way down to -27?C. in the depths of winter. Roofing materials have to be tough enough to cope with this extreme temperature swing, otherwise they degrade and ultimately fail.
Its durability and seamless application mean that it is one of the few membranes able to handle consistent heavy foot and vehicular traffic, including from Heavy Goods Vehicles, whilst still maintaining its waterproof integrity. Mastic asphalt is also easy to repair should alterations or damage occur.
More and more Mastic Asphalt Council (MAC) members are reporting innovative and modern uses of mastic asphalt. For example, Guaranteed Asphalt has completed over 50 projects across the UK whereby a hot melt system has been applied to the roof first prior to the application of mastic asphalt. This allows roofs to be loaded and the mastic asphalt protects the hot melt system underneath, even on substrates subject to traffic where vehicular access is needed.
Sussex Asphalte has also completed roofing projects whereby mastic asphalt is used as a working platform for other trades. One such project concerned the redevelopment of land at the former Queen Mary House in Chislehurst into retirement apartments. Located in an affluent suburb in south east London, Queen Mary House closed after 143 years of providing a home to retired Governesses and teachers. It was subsequently transformed by McCarthy & Stone into a development of luxury one and two bedroom apartments for those over 70.
During the redevelopment work, Sussex Asphalte applied mastic asphalt to the flat roof areas. For several months it was used as a loading bay for other trades people such as the roof tilers, bricklayers and scaffolders. Despite heavy materials such as bricks and plant repeatedly being placed on the roof during construction work, there were only very small indentations that needed minor repairs prior to finishing with two coats of solar reflective paint.
John O’Neill, Senior Site Manager at McCarthy & Stone said: “Originally a single ply roofing system was specified for the Queen Mary House project at Chislehurst but we changed it as it just wasn’t fit for purpose. Single ply is very much weather dependent and isn’t intended for walking on, plus we’ve previously had issues with leaks. We overturned the specification to mastic asphalt as it is tried and tested. Once mastic asphalt is down, it’s down and it’s very difficult to damage it. In the event that you do damage it, it’s very easy to repair.
“At McCarthy & Stone, we’re involved in some very large developments and as well as the project at Chislehurst, we’ve used Sussex Asphalte for several other projects where mastic asphalt has been used and have always been extremely happy with it,” he continued.
Julian Coulter, Director of Sussex Asphalt added: “Mastic asphalt can be used on central roofs and gutters where all other pitched roof areas and parapet walls can be reached with ease from this base, due to its robust nature and its resistance to puncturing. Although this is far from a traditional use of mastic asphalt, it outperforms any other roofing material when used as a loading or working platform. This simply wouldn’t be possible with alternative roofing systems such as PVC single ply membrane.”
When repairs are carried out on mastic asphalt, the intention of repair work should be to restore the asphalt to its original condition and ensure its continuing performance.
This article featured in the November issue of RCi magazine – click here to view the publication online.