Case Study – Sheet Piling Infill Insulation | Durham Light Infantry Museum Extension
From failing roof to finished system
The Challenge
Duratite were appointed by Cook Group Limited to design and deliver a technically advanced insulation solution to the steel sheet piling infill sections forming part of the Durham Light Infantry Museum Extension. The below-ground retaining structure required a system capable of providing exceptional thermal performance, moisture resistance, and substrate protection, while also simplifying installation compared to traditional shotcrete systems.
Conventional shotcrete methods were rejected by the project engineers due to their lengthy curing times, need for steel reinforcement, and inability to provide an effective thermal barrier. Instead, Enverge Nexseal LE closed-cell spray foam was specified as a next-generation alternative, combining high-density structural rigidity with superior insulating performance and rapid on-site application
Project file
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The Solution — step by step
System Specification
VP Foam Spray, an approved Duratite contractor, carried out the installation over three days, applying an average of 420mm of Enverge Nexseal LE Closed-Cell Spray Foam Insulation directly to the AZ 18-700 9mm steel sheet piling infills.
The foam was applied in multiple passes of up to 100mm per lift, with a minimum 15-minute cooling interval between applications to ensure complete chemical curing and interlayer bonding. Thanks to Nexseal LE’s low-exothermic reaction chemistry, thicker and more consistent builds were achievable without risk of charring, shrinkage, or thermal stress cracking — a key advantage over cheaper, high-exotherm European foams, which often limit application to 50–75mm per pass.
This low-heat reaction profile allows Nexseal LE to expand and stabilise uniformly across large-scale vertical surfaces, delivering a denser, smoother, and dimensionally stable finish that maintains adhesion even under hydrostatic pressure.
Once the recessed rebates were fully insulated, VP Foam Spray applied an additional 42mm continuous layer of Nexseal LE across the entire face of the sheet piling wall to create a monolithic thermal envelope. This ensured complete continuity between the infills and outer face, removing any potential cold bridges or thermal weak points.
To protect the exposed insulation during the construction period, the foam was overcoated with Bostik Idenden ET150 Grey Elastomeric Coating, providing UV stability, moisture resistance, and surface durability. The ET150 layer prevented discolouration and surface degradation while the spray foam remained exposed to the elements for several months prior to backfilling.
The Outcome
- Thermal Conductivity: 0.027 W/m·K — providing superior insulation in confined structural applications.
- Low-Exotherm Reaction: Nexseal LE’s advanced chemistry minimises internal heat generation during polymerisation, enabling thicker lifts per pass and faster build-up compared to most closed-cell systems.
- Dimensional Stability: Reduced exotherm and controlled reactivity prevent internal tension and surface shrinkage, ensuring long-term adhesion to steel substrates.
- Shotcrete Alternative: Eliminates reinforcement, formwork, and drying delays, saving significant programme time and cost.
- Structural Integrity: High compressive strength foam provides additional rigidity and impact resistance to the sheet pile assembly.
- Monolithic Continuity: 42mm face layer created a seamless thermal bridge-free barrier across the entire wall system.
- Moisture & Vapour Control: Closed-cell structure resists water ingress, frost action, and interstitial condensation.
- UV & Environmental Protection: Bostik Idenden ET150 coating ensures surface stability during prolonged exposure.
- Rapid Installation: Full application completed within 3 days, including curing, coating, and inspection.
The Durham Light Infantry Museum Extension project showcased the capability of Enverge Nexseal LE as a high-performance alternative to conventional ground-retaining wall insulation methods. The system provided the structural resilience and moisture protection required for permanent below-ground conditions while delivering a superior thermal envelope and drastically reducing site programme times.
By utilising Nexseal LE’s low-exotherm formulation, VP Foam Spray achieved rapid layer build-up and exceptional consistency — outperforming many imported closed-cell foams that lack the same precision chemistry and are prone to overheating or delamination in deep-section applications.
The final installation delivered a durable, UV-protected, and thermally continuous insulation system, fully bonded to the steel substrate and ready for long-term service life — setting a new benchmark for sheet piling infill insulation within the UK’s construction and infrastructure sectors.
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