Brick cleaning guide
How to clean an old brick wall
Old brick walls require a fundamentally different approach to modern brickwork. The characteristics that make historic brick beautiful also make it vulnerable to the cleaning methods that are safe on denser modern masonry. Getting this wrong causes permanent damage. This guide explains how to clean old brickwork correctly.
The vast majority of London's residential and commercial brickwork dates from the Victorian and Edwardian periods, making the ability to clean old brick wall surfaces correctly one of the most important skills in London property maintenance. The principles that govern safe cleaning of old brickwork are rooted in an understanding of how these walls were built, what materials were used and how those materials behave differently from the harder, denser construction found in post-war and modern buildings. The three key differences that determine the approach are the softness of the brick, the composition of the mortar and the presence of the fire skin on the brick face.
Fire skin
historic bricks have a dense fired outer skin that cannot be restored once damaged by abrasive cleaning or high-pressure water
Lime mortar
softer than the surrounding brick and highly susceptible to erosion from high-pressure water and harsh chemical cleaners
Test patch
any cleaning method or product on old brickwork must be tested on a discreet area before full application to the wall
The methods that cause irreversible damage to old brick walls
Before covering what works, it is worth being explicit about what must be avoided. The following approaches are commonly used on modern brickwork and cause permanent damage when applied to old brick:
High-pressure water washing
Erodes the fire skin of soft Victorian brick, blows lime mortar from the joints and forces water deep into a wall that was never built with damp-proof courses. The damage is permanent and cannot be undone.
Strong acid cleaners undiluted
Muriatic acid at working strength attacks lime mortar as aggressively as it attacks the contamination on the brick surface. It can permanently stain and etch softer brick types and causes rapid deterioration of lime joints.
Wire brushes or metal tools
Metal brush bristles scratch the fire skin and leave rust deposits in the scratches over time. They are never appropriate on any historic clay brick, regardless of contamination type.
Waterproof or non-breathable sealants
Old solid brick walls manage moisture by absorbing it during wet weather and releasing it during dry periods. Applying a non-breathable coating traps this moisture in the wall, accelerating mortar failure and causing brick spalling within years.
How to clean an old brick wall correctly
Step 1: Assessment and test patch
Before selecting any cleaning method or product, carry out a thorough assessment of the brickwork. Identify the brick type, establish whether the mortar is lime-based or Portland cement, identify the types and extent of contamination present and carry out a test patch in a discreet area with the proposed cleaning approach. Observe the test patch result for a minimum of 24 hours before proceeding. Any adverse reaction, such as surface etching, colour change or mortar damage, means the method or product strength must be adjusted before full application.
Step 2: Pre-wet the entire wall thoroughly
Thoroughly saturating old brickwork with clean water before applying any chemical cleaning product is critical. Pre-wetting serves two functions: it limits the chemical activity of the cleaning agent to the surface of the brick rather than allowing it to be drawn deep into the porous brick body, and it hydrates the lime mortar to reduce its vulnerability to chemical erosion. This step must never be skipped when cleaning old brickwork with any chemical product.
Step 3: DOFF steam cleaning for biological growth and general soiling
For general soiling, algae, moss and light carbon contamination on old brickwork, DOFF superheated steam cleaning is the safest and most effective professional approach. The system delivers steam at up to 150 degrees Celsius at very low pressure, which removes contamination through heat rather than force. It does not saturate the wall, does not erode the fire skin and does not disturb lime mortar joints. DOFF is the professional standard for listed buildings and conservation areas across London.
Step 4: Chemical cleaning for deeper carbon staining where steam is insufficient
For deeply embedded Victorian carbon staining that DOFF alone cannot fully lift, controlled chemical cleaning using specialist masonry cleaning products at low concentration may be used in addition. The chemistry must be selected based on the specific contamination type and brick composition. Products are applied at the lowest effective concentration, given short dwell times and rinsed thoroughly at non-damaging pressure. A gel or thixotropic product is preferable to a liquid solution on old brickwork as it controls absorption and prevents excessive chemical penetration into the brick pores.
Step 5: Thorough rinsing from top to bottom
Complete the clean with a thorough rinse using a wide fan nozzle at low pressure from the top of the wall downwards. All cleaning product residue must be fully removed from both the brick face and the mortar joints. Residues left in joints can continue to react with the mortar over time, causing ongoing deterioration even after the cleaning work has been completed.
Managing expectations for old brickwork cleaning
It is important to have realistic expectations when cleaning very old brickwork. A wall that has accumulated 100 years or more of carbon deposits will not return to the appearance of new brickwork after a single clean. The original colour variation of the brick will be revealed, and much of the dark soiling will be removed, but some traces of historical patina will remain, particularly in deeper pores and protected ledges. This is not a failure of the cleaning process. It is an appropriate outcome for historic masonry that should be preserved rather than aggressively stripped. The goal is to reveal the original character of the brickwork, not to make it indistinguishable from new construction.
Brick cleaning London
Old brickwork cleaning across London by Cloud Nine
Cloud Nine specialises in the cleaning of period and old brickwork across London using heritage-safe methods including DOFF steam cleaning. We carry out a thorough assessment and test patch on every project before committing to full-scale cleaning. Contact us for a free assessment and quote.
Part of our guide
Brick cleaning help and guidance
Everything you need to know about brick cleaning for London properties.
Back to the guide