Brick cleaning guide
Is brick cleaning safe for older London buildings
Brick cleaning is entirely safe for older London buildings when the correct method is chosen for the brick type, mortar age and contamination present. When the wrong method is used, the damage can be severe and irreversible. This guide explains what works and what to avoid.
The majority of London's residential housing stock dates from the Victorian and Edwardian periods. These buildings were constructed using soft clay brick joined with lime mortar, a combination that is fundamentally different in its characteristics from modern brick construction. Understanding those differences is the key to answering whether brick cleaning is safe for older properties. The short answer is yes, when the right method is selected. When the wrong method is used, whether high-pressure water washing, abrasive sandblasting or aggressive chemical treatment, the damage to both the brick face and the lime mortar joints can be permanent and costly to rectify.
Fire skin
historic bricks have a dense outer fired skin that must never be disturbed by abrasive or high-pressure cleaning methods
150 degrees C
temperature of DOFF superheated steam, which removes contamination through heat rather than pressure, preserving historic surfaces
Test patch
every professional brick cleaning project on an older London property must begin with a test patch before any full-scale cleaning
What makes Victorian and Edwardian brickwork vulnerable
Victorian and Edwardian London properties were built with hand-made or wire-cut clay bricks considerably softer than modern machine-pressed equivalents. These bricks develop a dense outer layer during kiln firing called the fire skin, which gives them their characteristic surface texture and colour variation. This fire skin is the hardest part of the brick but it is also thin, and once removed by abrasive cleaning or high-pressure water, it cannot be restored. Beneath the fire skin, the brick body is significantly softer and porous. When the fire skin is damaged, the brick absorbs moisture far more readily, dramatically accelerating future contamination and increasing the risk of frost damage and spalling.
The mortar used in Victorian buildings is lime-based rather than the Portland cement mortar used in modern construction. Lime mortar is deliberately softer than the surrounding brick so that it can absorb micro-movements in the masonry, protecting the bricks from cracking. If lime mortar is eroded by high-pressure water or damaged by inappropriate chemical treatment, it must be removed and replaced with matching lime mortar. Using cement mortar as a replacement is a common mistake that traps moisture in the wall, accelerates brick deterioration and causes spalling within 5 to 10 years.
What causes permanent damageMethods that can permanently damage older brickwork
High-pressure water washing
Forcing water at high pressure against soft Victorian brick erodes the fire skin, blows mortar from the joints and drives water deep into the masonry. This is the most common cause of damage to older brickwork from cleaning. It is also ineffective for removing chemically bonded carbon deposits, which high pressure cannot dissolve.
Sandblasting
Traditional dry sandblasting removes the fire skin of historic brick completely and permanently. It rounds off sharp brick arises, degrades architectural detail and leaves the underlying brick body exposed to moisture. It also creates significant dust containing respirable silica. Sandblasting is not appropriate for any historic brickwork.
Strong acid cleaners
Muriatic acid and high-concentration hydrofluoric acid solutions attack lime mortar as well as the contamination on the brick surface. They can permanently stain, etch and pit softer brick types and will rapidly degrade lime mortar joints even at moderate concentrations. Acid must only be used at carefully controlled low strengths by experienced operators on appropriate brick types.
Applying non-breathable sealants
Masonry paint and non-breathable sealants trap moisture within the brickwork, preventing the natural drying cycle that solid brick walls depend on. This leads to rising damp, accelerated mortar failure and eventually brick spalling. Historic brick must always be treated with breathable, vapour-permeable products only.
What is safe for older London brickwork
DOFF superheated steam cleaning
DOFF cleaning uses superheated water vapour at up to 150 degrees Celsius delivered at extremely low pressure. The heat breaks down biological growth, loosens pollution deposits and sanitises the surface, while the low pressure ensures the brick face, fire skin and lime mortar joints are not disturbed. DOFF is approved by English Heritage and conservation bodies for use on listed buildings and within conservation areas. It is the professional standard for period brickwork cleaning in London. Because DOFF uses only water, it leaves no chemical residue and dries rapidly, avoiding the saturation risks associated with water-based cleaning methods.
Low-concentration chemical cleaning with pre-wetting and rinsing
Where DOFF steam is not sufficient to remove deeply embedded carbon staining, carefully selected chemical cleaning products can be used at controlled low concentrations. The wall must be thoroughly pre-wetted before application to limit the chemical activity to the surface only. Dwell times must be kept short and rinsing must be thorough. This approach requires an experienced contractor who understands the specific chemistry of the products being used in relation to the brick type and mortar present.
Low-pressure wet abrasive systems
For removing paint and coatings from older brickwork, low-pressure wet abrasive systems such as TORC and vortex cleaning deliver fine abrasive particles in a water stream at controlled low pressure. The water cushions the impact on the brick surface while the abrasive particles lift the coating. When operated correctly by a trained specialist, these systems can remove even thick paint layers without damaging soft historic brick or lime mortar.
Brick cleaning London
Heritage-safe brick cleaning across London by Cloud Nine
Cloud Nine uses conservation-safe methods including DOFF steam cleaning for period and listed properties across London. We assess the brick type and mortar composition before recommending any cleaning approach and carry out a test patch on every project. Contact us for a free assessment.
Part of our guide
Brick cleaning help and guidance
Everything you need to know about brick cleaning for London properties.
Back to the guide