DOFF steam cleaning is a superheated water system that strips moss, algae, dirt and old paint from masonry using very low pressure and very high temperature, rather than the brute force of a domestic power washer. It was developed for listed buildings and conservation work, where a jet-washer would flay soft sandstone or crack old lime mortar.
If you have heard the name mentioned by a surveyor, a conservation officer, or a cleaning contractor and want to know what it actually involves, here is a straight answer: how it works, what it is genuinely good for, and what it costs compared with the alternatives.
What DOFF Steam Cleaning Actually Is
DOFF is a trade name that has become the generic term for a class of steam cleaning machines used in the UK cleaning and restoration industry. The system heats water to around 150 degrees Celsius and delivers it at very low pressure, typically under 100 psi, compared with 2,000 to 3,000 psi from a standard pressure washer.
The heat does the work that pressure normally does. Moss, lichen, algae and grime are killed and loosened by the temperature, then lifted away with a light water flow and a stiff brush where needed. There is almost no abrasive force hitting the surface, which is the whole point.
What It Is Used For
DOFF cleaning is the standard method on sandstone, limestone, listed buildings, church masonry, and delicate render where a pressure washer would erode the surface or blast out old mortar joints. It is also widely used to strip flaking paint from stonework ahead of repainting or repointing, and to clean pavements and steps where high pressure would loosen jointing sand.
On ordinary domestic properties it is less commonly needed. Most modern brick, concrete tile roofs and standard render can be cleaned safely with a lower-pressure soft wash or a controlled pressure wash, which is quicker and cheaper. DOFF earns its place on softer, older, or protected surfaces where getting it wrong is expensive.
DOFF vs Pressure Washing vs Soft Washing
A pressure washer relies on mechanical force and can strip paint, erode soft stone, and blow water behind render or into brick joints if used carelessly. A soft wash uses a biocide-based cleaning solution at very low pressure to kill and remove organic growth, then relies on rinsing and time rather than heat. DOFF sits between the two in approach: it uses heat instead of chemical strength or mechanical force, so it is gentler on the substrate than both alternatives while still being highly effective on biological growth.
For a typical Victorian terrace with sandstone lintels and sills, a competent contractor will often combine methods: DOFF or soft wash on the stone detailing, and a controlled pressure wash or soft wash on the brick and rendered sections.
Cost and What to Expect
DOFF cleaning is slower and more labour-intensive than pressure washing because the operator works close to the surface at low flow rates, so it typically costs more per square metre. For a house frontage with stone detailing you might expect a price somewhere in the £600 to £2,000+ range depending on scale, access and how much stonework is involved; a full listed building elevation costs considerably more.
Ask any contractor quoting DOFF work whether they are trained on the equipment and have experience with your building type. It is a specialist skill, and a botched job on historic stone is very hard to put right.
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