This handsome Lakeland stone villa on the outskirts of Keswick had developed heavy moss and lichen accumulation across its Burlington slate roof, blocking valley gutters and causing water ingress at the eaves. Our specialist soft wash roof cleaning service removed decades of organic growth without dislodging a single slate, restoring both the appearance and the weatherproofing performance of this beautiful roof. As trusted roofers in Keswick, we regularly treat slate roofs throughout the northern Lake District.
The owner of this substantial four-bedroom villa near Fitz Park had been watching moss gradually take over the property's traditional Burlington slate roof for nearly a decade. What had started as scattered patches of bright green moss in the shadowed areas behind the chimney stacks had spread to cover approximately seventy percent of the main south-facing roof slope. The moss growth was particularly dense in the valley gutters between the main roof and the rear extension, where trapped moisture and leaf debris created ideal growing conditions. Several slates on the lower courses had begun to lift as moss roots worked underneath the overlaps, creating gaps that allowed driving rain to penetrate into the roof space. The valley gutters were so blocked with compacted moss that rainwater was overflowing directly onto the stone walls below, causing damp staining and early erosion of the lime mortar joints. The homeowner had been quoted for a full scaffold and manual clean by another contractor, but was concerned about the risk of slate breakage from foot traffic and mechanical scraping on the aged Burlington slates, some of which were over a hundred and twenty years old.
We designed a two-phase soft wash treatment programme that would eliminate all organic growth without any need for operatives to walk on the fragile slate surface. Phase one involved accessing the roof from a roof ladder system anchored at the ridge, allowing us to manually clear the heaviest moss accumulations from the valley gutters and lower slate courses by hand without standing on the slates themselves. This removed approximately two wheelbarrow loads of compacted organic matter that was too dense for chemical treatment alone. Phase two was the biocidal soft wash application — a professional-strength sodium hypochlorite solution applied through extended-reach spray lances from the roof ladder positions. The solution was applied systematically across each roof slope, working from ridge to eaves to ensure complete coverage. We paid particular attention to the areas behind both chimney stacks and the junction between the main roof and the rear extension, where moss regrowth would be fastest if any root systems survived. The treatment was left to work over a forty-eight hour period, during which the biocide continued to destroy remaining organic matter. We returned on the third day for a final low-pressure rinse that washed the dead moss residue into the gutters, which we then cleared and flushed through to the downpipes. The entire process was completed without a single slate being cracked, chipped, or displaced — a critical consideration on a roof of this age and heritage value.
The Burlington slate roof was transformed from a moss-covered mass back to the beautiful silver-blue finish that these premium Cumbrian slates are renowned for. The valley gutters were flowing freely for the first time in years, and the eaves damp staining began drying out within days of the treatment. The lifted slates on the lower courses settled back into position once the moss roots beneath them died off, eliminating the rain penetration without the need for individual slate repairs. Our biocidal treatment provides residual protection against regrowth for up to three years, and we recommended the homeowner consider a maintenance wash every thirty months to keep the roof in peak condition. The property now commands its position overlooking Keswick with the clean, distinguished appearance that a traditional Lakeland villa deserves. The homeowner subsequently asked us to treat the stone boundary walls and the detached felt-roofed garage using the same soft wash process.
The core of our soft wash treatment is a professional-strength sodium hypochlorite solution, diluted on site to the precise concentration required for natural slate substrates. This biocide works by destroying organic growth at the cellular level — killing moss, algae, and lichen root systems rather than merely stripping the visible surface growth. This is what gives soft washing its long-lasting results compared to pressure washing, which leaves root networks intact and ready to regrow within months. The concentration used on natural slate is carefully calibrated to be effective against all forms of organic growth while being completely safe for the slate itself, the lead flashings around the chimney stacks, and the cast iron guttering on this period property.
We used professional extended-reach spray lances that allowed the operative to apply the biocide solution evenly across the full width of each roof slope from a roof ladder position. The lances incorporate adjustable fan nozzles that produce a wide, low-pressure spray pattern — ensuring thorough coverage without concentrating force on any single point. This equipment is essential for treating natural slate roofs safely, as it eliminates the need to walk on fragile slates while still achieving the precise, even application that consistent results demand.
A specialist surfactant additive was blended with the biocide to improve adhesion on the smooth, low-porosity surface of Burlington slate. Without surfactant, the solution would sheet off the slate before the dwell time was complete, resulting in poor kill rates on the deeper-rooted moss colonies. After the forty-eight hour dwell period, we used a pH-neutral rinse solution during the final wash-down to neutralise any residual biocide before it entered the rainwater system, protecting both the cast iron guttering and the garden below.
If your slate roof is suffering from moss, algae, or lichen growth, our professional soft wash service can restore it safely and effectively. We work throughout Keswick, Cockermouth, Penrith, and the wider northern Lake District. Contact Mr Roofer today for a free, no-obligation quotation and expert advice on the best approach for your roof.
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