BLOG: Protecting our concrete heritage

Stuart Hicks at cold-applied liquid waterproofing specialist, Kemper System, discusses the specification and installation challenges during the renovation of a grade II listed building – St Thomas More Church.

While much modern architecture divides opinion, some 20th century buildings demonstrate extraordinary aesthetic vision which must be preserved as part of our built environment heritage. Such were the thoughts of owners of the grade II listed St Thomas More Church in the Sheldon area of Birmingham.

Built in 1969, the Roman Catholic Church building was experiencing severe water ingress, resulting in water leaking inside the church and onto the congregational seating below. This not only presented health and safety issues, but a solution needed to be developed in order to save its demise after the church was added to Historic England’s ‘At Risk’ register in 2015.


Although practically the design of the building was failing, aesthetically, the church still offered the local community, and visitors to its parish, the delight of its modern architecture.

The church was built entirely in-situ from cast concrete and the plan of the building is fan-shaped, with a dual-fin spire structure rising high above the altar. A reinforced concrete frame with stained glass was built for the auditorium area, as well as for the red brick chapel, sacristy, confessionals and baptistery to the side and rear of the church. The thick concrete frame also forms buttresses to the corners for support, and encloses two chunky water spouts to the front. The wall supports meet at the higher, rear side of a shallow stepped concrete roof, where they then rise into the tall concrete steeple.

The roof section of the church is of an unusual design. Asphalt was used to waterproof the existing substrate which had begun to fail, resulting in water leaking into the building below, and condensation was also beginning to build up on the windows.


Because of the unusual design of St Thomas More Church, Manchester-based architects Wood Goldstraw Yorath worked in close consultation with Kemper System to enhance the waterproofing performance by addressing leaks and U/V damage to the existing substrate, whilst also improving drainage and reducing the risk of standing water on the roof.

After a consultation period, Kemper System’s Stratex Warm Roof System with solvent-free Kemperol 2K-PUR waterproofing membrane for the glass and concrete terraced roof was specified.

Kemper System’s Stratex Warm Roof solution is an integrated warm roof, supplied as a complete system of matched components. It has a unique tongue and groove insulation board. The build-up of the Stratex Warm Roof System included a vapour control barrier, insulation with Kemperol 2K-PUR cold liquid applied waterproofing applied on top, ideal for application over concrete substrates.

In addition, because of the unconventional design of the roof structure, a lot of standing water had developed, causing the water ingress to impact on the building further. The technical team at Kemper System therefore also devised a series of drainage channels to address this volume of standing water, whereby excess water would be caught and drained off the building.


As primarily structural engineers, operatives at specialist conservation company Alliance Technical Services Ltd undertook thorough product and application training at Kemper System HQ in Warrington before installing the Stratex Warm Roof and Kemperol 2K-PUR waterproofing. Technical representatives from Kemper System also visited the site during the project to advise and support the installation team.

The conservation programme first involved remedial works to the structural concrete to address corrosion of the reinforcement steelwork along with glazing restoration. For the recovering of the roof sections with the Kemper System-designed solution, operatives removed the existing chippings on the roof ready to clean and prime the asphalt substrate, and installed a tapered Kempertherm PIR insulation board. This was adhered to each terrace section in such a way to create channels behind and either side of each piece of insulation.

The insulation comprised of a rigid PIR board, a dense closed-cell structure with a hard top which has a particularly low thermal conductivity of just 0.023W/mK. The vapour barrier, Kempershield, is a reinforced aluminium, self-adhesive layer, Class ‘O’ rated and particularly suitable for concrete decks.

Kemperol 2K-PUR was then specified for the waterproofing layer. The wet-on-wet, fleece reinforced liquid waterproofing system complemented this particular project, as the odourless solvent-free product meant less disruption for the local residents and congregation as there were no strong odour’s emitted from the product.


Following the complex refurbishment works, the parish at St Thomas More Church can rest assured their church will continue to remain watertight for the foreseeable future, providing a place or sanctuary and worship for many years to come.