The legacy of the historic Bodmin Jail

Built in the 1770s by military engineer Sir John Call and prisoners, the Bodmin Jail was considered a milestone in prison design and reform. Built using 20,000 tonnes of local Delank granite and stone, Bodmin Jail featured individual cells, segregated areas for male and female prisoners, hot water and light. This reformed design also included open spaces for prisoners to live and work for an income.

Nearly 100 years later, the jail was declared unfit for purpose. As a result, an entirely new prison is constructed with limestone mined from the nearby moor. Evolving with the ideals of prison reform at the time, this ‘total institution’ featured 220 cells with separate wings for men and women, a chapel and a new area for debtors.

Officially decommissioned in 1927 and sold at auction to demolition men, the jail survived attempts to blow it up, with the nearly metre-thick formidable walls proving too challenging to deconstruct. Despite various incarnations since its closure, it wasn’t until 2004 that works would begin to restore and reinvent a few areas of the jail into a historical exhibition. In 2015 Bodmin Jail would see its next evolution, with a £40 million investment to create a state-of-the-art attraction, four-star hotel, and restaurant within its Grade II listed facade. 

The challenge

The project presented many challenges. Due to demolition attempts, large areas of the jail had been without a roof for nearly a century, resulting in large sections falling to ruin. With exposure to the elements, what remained was heavily saturated with water, with ivy and other biological materials spread across the remaining masonry. Further, pigeons and multiple species of bats were now occupying the former cells.

Technical and aesthetic considerations

Keeping the history of the building and as many original features as possible was key to the project. From a technical perspective, protecting the historic fabric while significantly improving the walls’ thermal performance was imperative. To successfully convert the heavily saturated jail cells into luxury hotel rooms, the team focused on how to manage moisture efficiently. The product chosen would need to accommodate the hustle and bustle of a busy hotel and withstand a knock or two from guests’ suitcases while maintaining a sophisticated feel.

Modern insulation systems had the severe risk of restricting moisture movement, which would risk damage to the historic fabric and cause mould and other moisture-related issues. In addition, organic systems, such as woodfibre and cork, would be unlikely to cope with the extremely high moisture content of the walls without the fear of interstitial condensation and rot.

The solution

Working closely with the project team, Insulating Render was chosen for the jail’s internal rendering. Manufactured with Saint-Astier Lime, recycled aggregates and additives, Insulating Render would be highly breathable and flexible whilst still providing the durability required. Additionally, as a mineral-based render, the lack of organic content meant that the render would not break down under extremely high moisture loads.

The next challenge was approaching the 100,000 tonnes of render to be applied. With pressing timelines, Insulating Render would allow the team to work quickly and apply thicker coats, significantly reducing the application time required. Designed with lightweight features, Insulating Render could be applied directly onto the stonework and built out in depths of up to 50mm per pass and over 70mm as a total depth, with just a week between coats. The walls were either left bare or finished with Superfine Lime Putty Finishing Plaster for the final finish.

To ensure the jail’s characterful stonework received the attention and durability it deserved, a mortar sample was tested to determine the binder and aggregate type. Once the analysis was complete, a mortar was designed and developed to match the original colour found within the masonry and used extensively for internal and external re-pointing.

The result

Due to Insulating Render’s porosity, the render began to pull water out of the background substrate, assisting the heavily saturated walls in drying. This breathability will continue to buffer relative humidity and manage the risk of condensation and mould while improving air quality. Further, the hotel will be able to provide the thermal comfort expected of a luxury four-star hotel. With its superior insulating properties, a 70mm coat achieved a U Value of 0.7, which was needed for the hotel’s complex heating, ventilation and cooling systems.

Since opening, Bodmin Jail has been nominated for several awards by organisations, including The Cornwall Tourism Awards, Visit England and the Royal Institution of Chartered Surveyors (RICS).