Mastic asphalt has recently been used to effectively waterproof Stirling Castle – one of Scotland’s most iconic historic properties. Its location is said to rival even Edinburgh Castle as it sits on volcanic rock, dominating the skyline for miles around.

An example of Renaissance architecture, this 16th century castle was home to generations of Scottish monarchs including Mary Queen of Scots. Most of the castle dates back to the period between 1496 and 1583. Now in the care of Historic Environment Scotland, visitors can look out from its high stone walls to the battlefields of Stirling Bridge where medieval armies clashed to decide the fate of nations.

Mastic asphalt is an integral part of our nation’s heritage, with the longevity and waterproofing properties necessary to preserve and protect historic and prestigious buildings across the UK.

Stirling CastleAuthentic materials for the conservation of heritage buildings and structures must not only retain the character, but also prove long-lasting and highly effective. Mastic asphalt, whilst a traditional waterproofing material that was first patented in 1837, offers durability and wear resistance far beyond modern alternatives which is why it is so frequently specified for refurbishment projects by the National Trust, English Heritage and Historic Environment Scotland, as well as other public and private owners of prestigious buildings.

Traditionally consisting of graded limestone aggregate bound together with bitumen, today’s mastic asphalt systems are now manufactured using 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. The incorporation of modern polymers into mastic asphalt systems has helped lead to its resurgence in the construction industry. Mastic asphalt is manufactured in the UK.

Specialist roofing contractor Greenroof UK, which specialises in the installation and maintenance of roofing systems in Scotland, was appointed to carry out the waterproofing work at Stirling Castle. Greenroof UK has been a contractor member of the Mastic Asphalt Council (MAC) since 2006.

The company aligns itself with the world’s leading manufacturers of roofing systems, combining environmentally friendly materials with traditional products. This approach achieves the most sustainable and cost-effective roofing solutions for Greenroof’s clients.

In the refurbishment project at Stirling Castle, effective waterproofing was required on the area over the casemates – the areas in the fortress wall with openings from which guns or missiles were previously fired. Signs of water ingress were evident and the areas beneath were damp.

The refurbishment project posed some challenges as an overburden to the roof had to be removed to expose the waterproofing. Removing the overburden revealed uneven levels and issues connected to the rainwater drainage.

Greenroof UK built up and evened out any water checks and repaired the rainwater drainage before reinstating mastic asphalt waterproofing. A mastic asphalt screed was first applied to provide a quick and effective levelling repair dovetailing in with the existing cementitious screed. This provided a stable base for the waterproofing works following immediately.

A specialist waterproofing system – IKO’s polymer modified mastic asphalt system Permaphalt – was then applied over a separation layer. The mastic asphalt system was installed to the details and upstands to complete the works and provide a continuous monolithic finish.

Providing completely seamless waterproofing, mastic asphalt can be installed in cold weather conditions and is virtually incombustible. This project was completed between February and March 2022 when daytime maximum temperatures averaged around 6°C. Suitable for roofs exposed to foot traffic, it is also environmentally non-polluting with zero carbon properties.

The mastic asphalt will provide a waterproof surface for years to come and maintain the aesthetic appearance of the original castle construction.

This article featured within the October 2022 edition of RCi magazine – click here to view the article.