What is DOFF cleaning?
DOFF is a superheated cleaning system from Stonehealth, designed for stone and brickwork. The machine heats a small volume of water to up to 150°C at the nozzle, and the operator adjusts the temperature and pressure to suit the surface and what’s being removed.
The heat does most of the work, rather than the force of the water. Trade magazine Stone Specialist explains the benefits: the low water volume means the surface isn’t saturated and dries within minutes, and the heat kills biological growth and spores, so no chemical biocide is needed.
You’ll often see it called DOFF steam cleaning. It’s much hotter than ordinary hot-water cleaning, and it’s a specific system rather than a general term for any steam cleaner.
How is DOFF different from pressure washing?
A DOFF machine can look like a pressure washer, but it cleans in a very different way.
| DOFF cleaning | Pressure washing | |
|---|---|---|
| What does the cleaning | Heat, with low pressure at the surface | The force of the water |
| Water use | Low: about 5 litres a minute on the DOFF III | Usually more |
| Drying time | Usually minutes | Longer, because more water goes in |
| Moss, algae and fungi | Killed by the heat | Washed off the surface |
| Best suited to | Stone and brick that force could damage | Tougher surfaces such as concrete and yards |
Pressure washing still has its place. If the surface is tough and the dirt is ordinary, pressure washing may be all you need.
What can DOFF cleaning remove?
The DOFF III product listing includes:
- Algae, moss and fungi
- Most oil and plastic paint coatings
- Certain types of graffiti
- Bird and vermin fouling
- Wax coatings and chewing gum
- Bitumen, oil and grease
We use it to remove mould, graffiti and discolouration from stone and brickwork. Results vary with the surface and the coating, so it’s worth testing before you commit to a whole elevation.
If there’s a large build-up of droppings, it should be removed before any surface cleaning. See pigeon guano removal. For graffiti on other surfaces, see graffiti removal.
What surfaces can it be used on?
The same listing names brick, stone, concrete, glazed and encaustic tiles, wood, faience and terracotta. Being on that list doesn’t make every building suitable, because condition matters as much as material.
We use DOFF on stone and brickwork, including at high level. It’s one of several methods we can use on a building facade.
When should you use DOFF cleaning?
DOFF is worth considering when:
- High pressure could damage the surface, for example on older stone or brick that’s still in sound condition
- Moss, algae or fungi are the main problem and you’d rather not use a biocide
- You need to remove paint or graffiti from masonry
- Too much water would be a problem, because the building is occupied or needs to dry quickly
- The site has no water or power, as we can supply both
When is DOFF cleaning the wrong choice?
It isn’t right for every job:
- Delicate or decaying stone, and old limewash: one conservation contractor, Minerva, says DOFF isn’t suitable for these. If the surface is flaking or crumbling, get advice from a conservation specialist before any cleaning.
- Old paint that could contain lead: HSE says lead was widely used in paint until the 1960s, and wasn’t removed from all commonly used paint until the early 1980s. It advises leaving sound paintwork in place. If old paint has to come off, have it tested first.
- Tough surfaces with ordinary dirt: concrete, yards and car parks may not need a specialist system.
Do you need consent to DOFF clean a listed building?
You might. The Building Conservation Directory says cleaning a listed building may be deemed an alteration, which can require listed building consent, or a faculty for a church. That can apply to paint removal and to trial cleaning.
Doing work without consent can be an offence, as Oxford City Council warns, so speak to your council’s conservation officer before anyone starts, even on a test area.
The same article says test panels are a normal part of the consent process. A panel should be discreet, but it must also represent the surface, the dirt and the detail on the rest of the building. Judge it when it’s fully dry, because damp stone looks cleaner than it is.
What is a Rosette approved DOFF contractor?
Stonehealth runs a contractor scheme called Rosette, and Stone Specialist notes that the work should be carried out by trained operators through it. Locus Services is a Stonehealth Rosette approved contractor.
Whoever you use, ask for:
- Evidence of their DOFF training or approval
- A test area before the main clean
- Before and after photos
- Risk assessments, method statements and proof of insurance
What does a DOFF clean involve?
Every building is different, but our DOFF cleaning service usually follows these steps:
- Site survey: we look at the surfaces, their condition, the access and what needs to be removed.
- Consent and test area: you confirm any consents you need, and we clean a small area so you can see the result.
- Planning: you get risk assessments and method statements, and we arrange access, including for high level work.
- The clean: our operators adjust the temperature and pressure as they work across the surface.
- Photos: all work is photographed before and after.
We operate 24 hours a day, 7 days a week, so we can work around your building’s hours.
