DOFF cleaning is a low-pressure, high-temperature steam-cleaning system primarily used to clean delicate exterior building surfaces. DOFF cleaning is popular in the UK for heritage, listed, and sensitive stonework
Unlike pressure washing or abrasive methods, DOFF uses extremely high temperatures (up to 150°C at the nozzle), very low pressure, and minimal water use.
The DOFF combination gently lifts dirt, paint, algae, and pollutants without damaging the surface.
Because DOFF cleaning uses heat and steam rather than chemicals, it is a gentle, environmentally friendly method for cleaning stone and brickwork. Chemicals are rarely needed and only used where necessary, like:
The DOFF method is ideal for the cleaning of:
DOFF cleaning is commonly used on a variety of surfaces, including limestone, sandstone, brickwork, terracotta, render, and concrete.
When you compare DOFF cleaning to pressure washing, several key differences emerge. DOFF cleaning uses low pressure and high heat, making it gentle on surfaces and ideal for heritage structures.
In contrast, pressure washing operates at high pressure and uses cold or warm water, which can potentially damage stone and mortar.
While DOFF cleaning is best suited for delicate, historical materials, pressure washing is more effective for cleaning hard, modern surfaces.
The DOFF machine is a specialist superheated steam cleaning system designed for gentle exterior cleaning, particularly on historic, listed, and delicate masonry. Its defining feature is the ability to deliver very high temperatures of up to 150°C at the nozzle, at very low pressure, while using minimal water.
The high heat and low pressure remove contaminants without eroding the surface, unlike pressure washing or abrasive systems.
Physically, a DOFF system is industrial yet compact; ours consists of the main unit, hoses, a lance, and the power and water supply. The main unit is a robust, metal-bodied machine, usually mounted on wheels or a trolley, and is roughly the size of a large generator or site compressor.
The DOFF cleaning machine contains a high-capacity water boiler, heating elements, and control systems for temperature and flow.
It features a strong, heat-resistant hose and a metal lance with interchangeable nozzles that help control steam temperature, flow rate, and spray pattern for various surfaces.
The DOFF machine is connected to an electrical power source, which is sometimes a generator that we bring on site. Additionally, it requires a mains- or tank-fed water supply.
When operating, the DOFF machine produces very little visible spray, often just a light mist and steam, making it noticeably quieter and less aggressive than pressure washing.
The DOFF machine works by allowing water to enter the unit and be superheated, with heat retained right up to the nozzle.
The steam then exits at high temperature but low force, softening, detaching, and gently lifting away dirt, paint, algae, and pollutants. The surface is left clean, intact, and minimally saturated.
The DOFF cleaning system originated in conservation and was developed to clean historic stonework without causing damage. Traditional methods, such as acid cleaning and sandblasting, were found to damage the surface patina and mortar and accelerate long-term decay.
As a result, DOFF emerged as a conservation-led solution engineered to meet the standards required for listed buildings, churches, monuments, and heritage façades.
DOFF cleaning follows a careful, staged process designed to protect the building fabric while achieving effective results.
We start with an assessment and test patch, followed by careful steam cleaning in sections using low pressure and high heat. The process is controlled and non-abrasive, making it ideal for stone and heritage buildings.
Below is the typical workflow we use as a professional DOFF cleaning contractor, particularly for heritage and commercial projects.
When inspecting the building, it’s important to thoroughly examine the materials used, such as the type of stone, brick, and mortar, to identify various forms of soiling like pollution, algae, paint, or carbon accumulation.
We note any areas that may be fragile or have previously been repaired. Consider the inspection access requirements, such as scaffolding or mobile elevating work platforms (MEWPs), and confirm any conservation or listed building constraints that may apply.
Before proceeding with the main task, it’s important that we conduct a small test panel in a discreet area. During this test, we adjust the heat level, water flow, and technique to determine the best approach to cleaning the area.
We confirm that the desired visual outcome can be achieved with no surface damage, so we must then secure approval from the client or conservation officer if required.
When we work at a site, we may need to first erect scaffolding or access equipment and protect sensitive areas with sheeting. We then set up our tools, including the DOFF machine, along with a reliable water supply and a power source, such as a generator. We may also need to ensure safe work zones are established to protect all personnel.
Our DOFF cleaning operatives work in controlled sections when applying the steam. We use low pressure and high temperature, making slow, methodical passes to gently lift contaminants. For stubborn areas, multiple light passes may be necessary, but aggressive scrubbing or blasting is avoided to ensure a safe and effective cleaning process.
Where issues include heavy staining, graffiti remnants, and carbon build-up, we provide localised attention. In some cases, DOFF cleaning is combined with mild poultices or low-impact chemical treatments, but these are used sparingly to ensure a careful approach.
After cleaning, we lightly rinse the surface if necessary and inspect the cleaned areas. We like to check the finish to ensure there’s no surface damage, and confirm there’s no residue or streaking.
If you want more treatment, we can use biocides to slow down regrowth or apply coatings that protect against graffiti. We will only do this in approved areas where it is appropriate.
DOFF cleaning requires the right technique and equipment. If the heat levels or distances are wrong, the results can suffer. It’s also important not to over-clean, as this can damage the surface’s patina. Proper preparation is key to preserving the surface for the long term.
DOFF cleaning is widely referenced by UK conservation officers and specifiers for its numerous benefits. It is non-abrasive, which helps to preserve fragile surfaces, and in most cases, it does not require chemicals.
The DOFF cleaning method effectively kills spores and algae at the root, minimising the risk of water ingress by minimising saturation.
Furthermore, it is approved for conservation work, making it a preferred choice for local authorities and conservation officers who often specifically request this cleaning method.
DOFF cleaning is designed for long-term maintenance rather than routine cleaning. Typically, it is recommended every 5–10 years, depending on specific circumstances.
For historic and listed buildings, DOFF cleaning should occur every 8–15 years. This is often a one-time treatment associated with conservation or restoration efforts and major façade repairs. Care is taken to avoid over-cleaning to protect the historic patina.
Commercial stone and brick buildings generally require DOFF cleaning every 5–10 years. The frequency can vary based on factors such as traffic pollution, location (urban or rural), and building exposure. It’s often scheduled alongside planned maintenance.
In areas affected by algae, moss, or lichen, DOFF cleaning is recommended every 4–7 years. This method effectively kills off spores, slowing down regrowth compared to pressure washing. The timeline can be extended if an approved biocide treatment is applied.
For graffiti-affected areas, DOFF cleaning should be done as needed. Initially, the area is cleaned with DOFF, after which protective coatings can be applied to minimise future cleaning frequency.
The effectiveness of DOFF stems from its unique ability to kill root growth, limit water absorption, and maintain surface integrity without causing erosion. This ensures that cleaned surfaces remain cleaner longer than with more aggressive cleaning methods.
A key principle in conservation is to “clean as little as possible, and only when necessary.”
Even with methods like DOFF, cleaning should be based on the condition of the surface rather than its appearance. It’s essential to conduct a survey and a test patch before proceeding and to avoid using DOFF as a routine cleaning method.
DOFF cleaning can be carried out on building façades, walls, monuments, churches, and other stone or brick structures where a gentle, conservation-approved cleaning method is required.
As a specialist exterior cleaning company, we use DOFF cleaning and our specialist DOFF cleaning machine to assist organisations such as heritage and conservation contractors, local councils, commercial property managers, and managers of churches, monuments, and historic estates. But DOFF cleaning can be used for any property where cleaning needs to be a little more sympathetic, so it could be used on your patio or driveway. Contact us to see if DOFF cleaning is for you.
DOFF cleaning is considered one of the most environmentally responsible exterior cleaning methods. One key reason for this reputation is that it is chemical-free in most cases, making it a safe option for both the environment and the surfaces being cleaned.
Additionally, the DOFF method uses very little water, which is important for resource conservation. Its heat-based cleaning approach means that no detergents enter the drains, further minimising environmental impact.
The DOFF method effectively eliminates spores and algae, reducing the number of required treatments and improving environmental quality, in turn saving time and money.
Moreover, this method preserves the original surfaces of structures, reducing the need for long-term repairs.
Because of these benefits, DOFF cleaning is frequently approved by conservation officers, specified for use on listed buildings, and embraced by local authorities and heritage bodies.
DOFF does not stand for anything; it is not an acronym. The term “DOFF” originates from the brand name of the original DOFF cleaning system, which was developed for conservation and stone cleaning. Over time, “DOFF cleaning” has become a generic term in the UK, much like “Hoover” is used to refer to vacuuming.
There is a myth that DOFF is an acronym for terms like “Direct Output Forced Flow,” which is a common misconception.
DOFF cleaning is a gentle, heat-based method that cleans stone and brick without damaging the surface. It’s environmentally friendly, approved for heritage buildings, and delivers long-lasting results with minimal risk.
If you believe DOFF cleaning could benefit your project or property, we would be happy to discuss how we can assist with cleaning your area.
