Case Study:Stone Cleaning on a Landmark University Building

The Client

Our client for this project was an external window cleaning contractor responsible for maintaining the London School of Hygiene & Tropical Medicine (LSHTM) campus. Having partnered with Spectrum on a previous project at the school, cleaning the main entrance stonework, the contractor approached us once again, confident in our ability to deliver a safe, sensitive clean to this Grade II listed educational landmark.

The Site

Located on Keppel Street in Bloomsbury, the LSHTM building is one of London’s most recognisable academic institutions. Founded in 1899 and a constituent of the University of London, the school’s main building was completed in 1929 and remains largely unchanged. Its distinctive façade is adorned with a carved frieze honouring 23 pioneers of tropical medicine and public health.

Now Grade II listed, the building's stone features have significant architectural and heritage value. Maintaining its exterior is essential to upholding the legacy and ongoing operations of this world-renowned institution.

The Challenge

The stone ledges and sills along one side elevation had become heavily soiled with moss and biological growth, giving the surface a dark, patchy appearance. While the total surface area was relatively small, around 20m², the visual impact was significant on such a prestigious building.

Access presented its own complications. The working area was directly above a public footpath on a busy Central London street. To ensure safety, our team needed to manage exclusion zones and divert pedestrian traffic, without disrupting the school’s day to day operations.

To minimise risk and footfall interference, all works were scheduled for the weekend.

Our Approach

Our team recommended a gentle DOFF steam clean, a conservation-approved method that safely removes moss, algae and pollution from delicate stone surfaces without causing damage. The DOFF system was created by Stone Health and uses super-heated steam at lower pressure than typical pressure washers. This means it is far less likely to cause damage to natural materials, like stone, as the machinery is operated at a far lower PSI than usual.

Access was completed via our 27 meter van-mounted MEWP, positioned in a designated parking bay in front of the building. Due to changes in elevation during the clean, our team made careful adjustments to the DOFF equipment to maintain consistent pressure and steam temperature, expertise made possible thanks to our deep familiarity with the DOFF system.

While the scope of work focused on ledges and sills, our operatives also cleaned adjacent areas of the stone façade and paving to create a more uniform result. These additional touches helped restore the entire elevation, not just the isolated features.

The Result

The transformation was immediate. The stonework was no longer dulled by pollution and moss but instead restored to its original light tone, once again living up to the building’s historic character.

This project reflects Spectrum’s commitment to preserving the visual integrity of London’s most iconic buildings. Our considered, conservation-led approach ensures the façade of this landmark institution will continue to inspire future generations of researchers, students and visitors.

Why Spectrum

Although Spectrum was brought in by a third-party contractor to deliver this phase of stone cleaning, it’s worth noting that we are fully equipped to handle a far wider scope of external works. From high-level window cleaning to gutter maintenance, leak detection, roof repairs and more, we provide a comprehensive suite of building maintenance services entirely in-house.

This allows us to offer a streamlined, value-driven service where access, cleaning, and specialist repairs can all be managed by a single contractor. Our operatives are IRATA-certified, and we own and operate our own access equipment like MEWPs, rope systems and patented modular cleaning tools, which enables us to minimise disruption, reduce costs, and work smarter on every project.

For properties like the London School of Hygiene & Tropical Medicine, where heritage, safety and reputation matter especially, working with a multi-skilled, access-specialist partner like Spectrum ensures that building care is delivered with both precision and professionalism.