A fine, intermittent water mist applied over hours or days, not minutes. Nebulous spray is the gentlest method available for the most fragile historic stone — friable surfaces, decayed carving, and material where any other method risks losing what remains.
Nebulous spray — also called intermittent misting — applies a very fine water mist to a stone surface in timed cycles over an extended period, typically hours rather than minutes. The volume of water at any moment is tiny; the nozzles are calibrated to wet the surface without ever allowing water to run or pool. The mist slowly softens and loosens soiling and biological growth through gentle, repeated rehydration, with no mechanical action and no thermal stress at any point in the process.
It is, deliberately, the slowest method we offer. Where DOFF cleans a facade in days and TORC works through a programme of test panels and full application over a similar timescale, nebulous spray is measured in continuous cycles that can run for a full working day or longer on a single elevation, sometimes repeated over several days.
Nebulous spray is reserved for surfaces where even DOFF's low-pressure steam or poultice cleaning's localised application carry meaningful risk — badly decayed limestone where the surface is actively sugaring or friable, fine carved or sculptural detail in poor condition, and terracotta or faience elements where the fired surface has failed and the body beneath is exposed and vulnerable. This is not a method we reach for by default; it's specified when the condition of the material genuinely rules out anything more direct.
We also use nebulous spray where a conservation officer or a heritage consultant has specified minimum-intervention treatment as an explicit condition, typically on Grade I or Grade II* fabric where the priority is unambiguously preservation of what remains over achieving a fully clean appearance.
Nebulous spray removes soiling more gradually and, in some cases, less completely than DOFF, TORC, or poultice cleaning. That trade-off is the point — on the material it's specified for, the alternative isn't a better clean, it's a damaged or further-decayed surface. We set expectations honestly at the survey stage: this method protects the material first and cleans second.
Because the process runs continuously over an extended period, access and water management — drainage, protection of surrounding surfaces, and ensuring the mist reaches only the intended area — are planned in detail before work begins.
DOFF uses superheated steam at around 150°C, delivered directly and briefly. Nebulous spray uses cold or ambient-temperature water, delivered as a very fine mist in long, repeated cycles with no heat and no pressure beyond what's needed to atomise the water. It's a fundamentally gentler process, and correspondingly slower.
Because it's also the least effective method at removing general atmospheric soiling, and far slower than any alternative. For a facade in reasonable condition, DOFF or TORC will achieve a better result in a fraction of the time. Nebulous spray is specified when the stone's condition, not the soiling, is the deciding factor.
Significantly longer than any of our other cleaning methods. A single elevation can require a full day or more of continuous misting, sometimes repeated across several days depending on the condition of the stone and the extent of soiling. We provide a realistic programme, not a steam-cleaning timescale, as part of the written specification.
Yes, it's one of the situations where we specify it most often. Where the fired surface of terracotta or faience has failed and the underlying body is exposed, it becomes considerably more vulnerable to moisture and mechanical action, and nebulous spray is often the only cleaning method that doesn't risk accelerating further loss.