dinburgh is a city famed for its elegance and culture and the Royal Botanic Garden Edinburgh (RBGE), located just a mile outside the city, is part of that rich heritage.

Much more than a park, RBGE is a global centre of scientific and horticultural research and achievement covering a landscaped site that spans more than 70 acres and dates back to 1670. It has become a key visitor attraction for professional gardeners, keen amateurs and those who simply want to wander around the many unique features, which include the largest collection of wild-origin Chinese plants outside China, a world-famous ‘Rock Garden’ with more than 5000 alpine plants and the tallest Victorian glasshouse in Britain.

Ornamental gateway

For most visitors, a must-visit attraction is RBGE’s John Hope Gateway, which provides a biodiversity and information centre, with a ground floor exhibition space and first-floor restaurant.

The exhibition space and restaurant overlook a trio of terraced ornamental pools which were designed to cascade down into each other. However, pipework problems had prevented these pools from fulfilling their design intent and the lining material used had also failed. The ponds had originally been constructed to abut the edge of the building, which had also created challenges with cleaning the floor-to-ceiling windows of the exhibition space.

The combination of all these factors led to a decision to commission Water Gems (Alba) to carry out a refurbishment project that involved draining the pools, replacing the existing lining with Firestone’s PondGard lining and making changes to the pipework and pumping system. The scheme also involved the creation of a narrow walkway between the John Hope Gateway building facade and the water to enable future window cleaning and maintenance.

Complex geometry

The existing lining, a PVC-P system, had not been flexible enough to cope with the pool’s complex shape leading to failure of the joints and fixings. After draining the pool, the Water Gems team removed the gravel that had been used to ballast the existing pond lining, which was then stripped out.

The Water Gems team then excavated the pipework, cleaning and reconfiguring the existing pipe to provide a more effective solution for controlling the water flow and installing a new overflow pipe and filtration system, which was fitted with a timer to ensure energy-efficient operation.

With upgrades to the pipework layout completed, the Water Gems team backfilled onto the refurbished pipework then laid a geotextile membrane into the pond cavity, prior to installation of the new liner. The flexibility of Firestone’s PondGard EPDM lining system, supplied through UK distributor Gordon Low Products (an authorised distributor for Firestone PondGard EPDM), and its proven durability and service life as an extremely robust material made it ideally suited to the challenging installation.

At just 1mm thick, it could be folded into the corners and awkward angles of the pool’s complex geometry easily, without any risk of tearing or cracking. It also offered a chemically-inert, UV stable and temperature-stable solution that will resist algae growth and microorganisms.

Complete lining solution

The Water Gems team worked with Firestone to pre-calculate an optimised configuration for the PondGard lining material, which was cut and laid into the cavity with a 150mm lap on all joints. The joints were sealed using Firestone’s QuickSeam 3" Splice Tape, a self-adhesive tape that provides a permanent watertight seal between each section of liner.

Firestone Bonding Adhesive was used to adhere the liner to the concrete walls around the lower section of the pool and the Water Gems team used stainless steel straps connected to the granite walls at the top of the pools to allow the liner to be folded back onto itself and provide a robust mechanical fixing solution.

In the areas where the liner follows the cascade into the next pool, the detailing was completed using Firestone QuickSeam FormFlash, a factory-laminated self-adhesive flashing tape.

Long-term performance

Thanks to the refurbishment project, the ornamental pools at RBGE’s John Hope Gateway are now cascading beautifully, creating a feature that benefits this key viewpoint out towards the parkland.

With a service life of at least 40 years, the EPDM liner will retain its flexibility and waterproofing performance over time for RBGE visitors to enjoy for generations.