Superheated low-pressure steam at 150°C. The heritage-specified cleaning method for listed buildings, conservation areas, and ornate carved stonework across London.
DOFF is a steam cleaning system developed specifically for historic masonry. It produces superheated steam at temperatures up to 150°C delivered at low pressure — typically between 15 and 30 bar. The combination matters: the heat does the work, not the water. This keeps water ingress to a minimum, which is critical on porous stone and lime-mortared joints where prolonged wetting causes internal damage.
The system uses no cleaning chemicals in standard operation. It removes atmospheric pollution, biological growth, and surface soiling by thermal shock rather than chemical reaction or mechanical abrasion. What this means in practice: ornate carving, arrises, and fine surface tooling are preserved intact. No detail is lost to the cleaning process itself.
This is why DOFF has become the default specification for listed building restoration. Historic England recommends it. Conservation officers specify it. The method aligns with the minimum intervention principle that governs all work on designated heritage assets.
Atmospheric black crust is the most visible soiling on London's stone buildings — the sulphate-rich pollution layer that forms on sheltered areas where rain doesn't wash the surface. DOFF lifts this effectively from Portland stone and limestone.
Biological growth — algae, lichen, moss, black fungi — responds particularly well to the high temperature. The thermal shock kills organic matter at the root, not just at the surface. Growth doesn't recover in the short term from properly applied DOFF treatment.
General atmospheric soiling on exposed surfaces, calcium carbonate runoff, bird fouling, and surface contamination from adjacent building works.
DOFF is less effective on deeply calcified soiling, heavy paint, and some mineral staining types. These require TORC cleaning, poultice application, or a combination approach. We specify the right tool after survey — never the other way round.
The choice between DOFF and TORC is one of the most common questions we receive, and the honest answer is that it depends on the surface. DOFF is the appropriate primary method for carved stonework — columns, capitals, friezes, finials, decorative mouldings — where TORC's aggregate component risks rounding fine detail. DOFF is also preferred where the stone is soft, friable, or in fragile condition.
TORC becomes relevant where the soiling is thick, calcified, or where DOFF alone fails a test clean. On flat panel work, string courses, and robust Portland stone in heavily polluted areas, TORC is often the faster and more effective choice. Many restoration projects use both: DOFF on carved elements, TORC on plain surfaces.
Read the full comparison: DOFF vs TORC — how we choose the right method.
Working on a listed building requires a method statement submitted to and approved by the local authority conservation officer before any cleaning commences. This is not optional. Work carried out without consent on a listed building constitutes a criminal offence under the Planning (Listed Buildings and Conservation Areas) Act 1990.
We handle the method statement as part of our standard service. We have an established relationship with conservation officers across London boroughs and are familiar with the documentation requirements. A test clean is almost always required — we carry these out as part of the specification process, not as an extra charge.
On completion, we provide full written records: the method used, the areas treated, before and after photographic documentation, and the conservation officer approval reference. This forms part of the building's record and is required under the terms of listed building consent.
We begin every project with a free site visit: stone condition assessment, soiling identification, access planning, and a test clean on a representative sample area. The test clean is evaluated after 24 hours once the stone has dried — damp stone always looks cleaner than it is.
The specification we provide covers method, areas to be treated, expected programme, and cost. Once agreed, works proceed with the access arranged and conservation consent in place.
On site, operators work systematically across the facade, adjusting steam temperature and pressure as surface conditions vary. Carved areas receive slower, more precise passes. All run-off is controlled. Surrounding surfaces, windows, and landscaping are protected before work begins.
DOFF is a system of superheated low-pressure steam cleaning that operates at up to 150°C. The high temperature kills biological matter, loosens atmospheric pollution, and lifts surface soiling without requiring high water pressure or chemical cleaning agents. It was developed specifically for historic masonry.
DOFF cleaning is typically quoted per square metre after a site survey. Costs depend on access, stone condition, and the level of soiling. We provide written specifications with costs within 48 hours of a free site visit.
Yes. DOFF is the most commonly specified method for Grade I and Grade II listed buildings in England. It's approved by Historic England and is the default recommendation in most conservation officer method statements. The minimal water use and absence of chemicals make it the safest option for vulnerable historic fabric.
Neither is universally better. DOFF is appropriate for ornate carved stonework, delicate surfaces, and buildings where water ingress is a concern. TORC adds fine aggregate to the steam stream, increasing mechanical action for heavily carbonated surfaces or thick soiling. Many projects use both — TORC on flat panel work, DOFF on carved detail. We specify which based on the actual surface condition.
DOFF effectively removes atmospheric carbon pollution (the black soiling common on sheltered surfaces), biological growth (algae, lichen, moss), general surface dirt, and some mineral staining. It's less effective on deeply calcified soiling, paint, and certain mineral crusts — in those cases TORC or poultice cleaning is more appropriate.