Changing Perceptions in Material Specification

Although mastic asphalt is one of the world’s oldest construction materials, it can sometimes be perceived as a one-dimensional waterproofing product that is only available in a standard black finish. But like many longlasting, tried and tested materials, mastic asphalt is being re-imagined as a highly relevant building material for today.

Mastic asphalt is most commonly associated with flat roofing applications but due to its waterproofing properties, durability and versatility, it is being specified for a whole range of construction applications - both new build and refurbishment projects - where a seamless, durable surface is required.

One architectural designer who has realised the potential of mastic asphalt is Charlie Luxton, who specialises in sustainable architecture and design, with an overall aim of creating beautiful, energy efficient buildings that age gracefully and don’t cost the earth to build or maintain. Charlie combines his design work with presenting TV programmes such as ‘Building the Dream’ and ‘Homes by the Sea’.

As well as specifying mastic asphalt for client projects, Charlie has used mastic asphalt on the construction of his own home. Specifically on the build of a complex stair detail where the stairs descend through a flower bed. Mastic asphalt was used to form stairs, upstands, sumps and drainage outlets - a “hugely complex 3D object,” according to Charlie.

“This is what mastic asphalt can offer - waterproofing, a durable surface, even a decorative finish. I am a paid-up member of the mastic asphalt fan club,” he said. Building Charlie’s own house became a journey to embrace re-imagined older materials.

“Increasingly as I detail my buildings I am looking always for the most robust way of achieving beautiful finishes. Mastic asphalt is tough, with a long life span, and repairable. If the integrity of the covering is compromised or if you want to alter and make changes to the building over time you can easily repair with it and this makes it eminently suitable for the realities of building,” said Charlie.

He also refers to the environmental credentials of mastic asphalt.

“Mastic asphalt is 100% recyclable and inherently efficient to install. It was an eye opener on my build. The mastic asphalt guys used what they needed and took back what they didn’t, to reheat and reuse. No waste at all. Many alternative materials such as complex multi-layered roof membranes can be incredibly difficult to recycle and this is not likely to change anytime soon. We need to reduce waste first. Waste during build is hard to control but waste before installation is a huge issue too, with 10% of materials coming to building sites leaving in a skip,” he said.

Charlie advises specifiers to try to use more simple, less refined, inert products like wood fibres, lime and timber.

Passionate about sustainable architecture since he was a fresh-faced student in the early 90s, Charlie says urban areas, suburbia and gardens are all oases of bio-diversity and to support this green roofs played a huge role.

“I used to be sniffy about green roofs in the countryside but increasingly we are looking at their role to provide habitat. In towns they reduce the heat island effect, reduce particulates and provide much-needed wildlife refuges as well as reduce solar gain and control temperature fluctuation through the thermal mass they can provide.

“The big issue with green roofs is longevity and robust construction. Mastic asphalt with its longevity and robust nature is a great material for these green roofs. Buried under a few hundred millimetres of soil the life span of mastic should be impressive.”

Charlie also has his own take on skills shortages.

“The big issue is getting people who know how to install systems and materials well, whether it be MVHR, EDPM or tape and fill plasterboard. In principle they are all good but installed wrong they become a huge problem.

“I am increasingly aware of just how much time site issues can cost a practice. You can be very disciplined and smart through the design stage, planning, detailing and 95% of construction just to lose your hard-won profit when an installation goes wrong and you get into the quagmire of the blame game.

“Specifying robust materials that have a guaranteed level of craft from the people fitting them, especially when it comes to roofs, can be invaluable.

Watching the team install the mastic asphalt on my own build was fascinating. Seeing 15-20 mm of the black stuff going down and being sculpted into a stair and upstand was incredible.”

And on value-engineering.

“It’s about accepting that buildings have to last a long time. We need to be thinking about finishes that last 100 years, not 20. To need minimum maintenance over the long term. Clearly this has a cost implication but to fully understand this we need to think in terms of life cycle cost not just installation cost. And the life cycle cost of mastic asphalt is much lower than its competitors.”

As well as its robustness and longevity, Charlie said he also specified mastic asphalt for his own home for its versatility.

“It’s a material that can be a roof finish, a floor finish, deal with the complexities of stairs, is robust enough to be the stair finish itself, even in my case if just while construction is in process, and can then take a screw being dropped on it and trampled into the surface again, again and again.

“Doing my house spent time with waterproofing installers and I couldn’t help watching and finding out what is involved. They loved working with mastic asphalt, partly due to its flexibility. It was a fascinating craft.”

In conclusion, Charlie said: “Some of the most interesting and best new materials we are using in our office are the old ones. But sometimes you can think you’re looking backwards and it turns out you were looking forward.”