What these materials are, and where you find them
Terracotta is fired clay, shaped in moulds and kiln-fired at high temperature to produce a hard, dense material suitable for architectural ornament. From the 1870s onwards it became the standard alternative to carved stone for mass-produced architectural detail — capitals, keystones, column shafts, string courses, and the elaborate decorative programmes that characterise late-Victorian commercial buildings. The material was consistent, could be made to precise profiles in quantity, and was significantly cheaper than carved stone.
Faience is terracotta with a vitreous glaze applied and fired onto the surface. The glaze is hard and impermeable, which makes faience highly weather-resistant in theory. In practice, the glaze integrity is also its vulnerability: if the fired surface is disrupted by abrasive cleaning, chemical treatment, or thermal shock, the damage is permanent and visually obvious. The glossy surface of faience does not hide abrasion — it shows it.
Both materials appear widely across London. The richest concentrations are in the areas of late-Victorian commercial development: the City of London, the West End, Islington, Hackney, and the inner ring of Victorian borough high streets. The period pub buildings of the 1880s and 1890s are particularly likely to feature faience facades — the brewing companies used the material for its durability and its capacity to carry rich colour.
The specific problems with terracotta and faience
Soiling and biological growth
Unglazed terracotta is porous. It accumulates atmospheric soiling in the same way as stone — carbon deposits from combustion, biological growth in moist or sheltered areas, and salt efflorescence from water movement through the wall. The fine texture of terracotta can make soiling appear more severe than it is; the material absorbs and holds deposits in its surface pores rather than building up a surface layer.
Glazed faience, by contrast, does not absorb soiling into its surface. Deposits sit on top of the glaze and are generally easier to remove. The problem with faience soiling is usually at the joints rather than on the face: mortar and sealant joints that have failed allow water behind the glaze, causing staining from the substrate side that is not addressable by surface cleaning.
Cracking and joint failure
Terracotta cracks for several reasons. The most common are thermal movement — the material expands and contracts significantly with temperature change — and the rusting of any embedded metal fixings. Victorian terracotta was frequently fixed using iron cramps set into the wall behind. As iron corrodes, it expands, and the expanding corrosion product fractures the terracotta from behind. The crack pattern this produces is characteristic: radiating outward from a fixed point rather than running along a joint.
Failed mortar joints are the other major source of water ingress and subsequent cracking. The joints in terracotta facades were typically bedded and pointed in a lime mortar that matched the colour of the terracotta closely. Cement repointing — as with brick — is too hard and too rigid, and causes the same pattern of spalling and cracking that it causes in brickwork. The added problem with terracotta is that the material is thinner and more brittle than most bricks, so the damage accumulates faster.
Original lime mortar joints in Victorian terracotta are usually buff or cream in colour, with a slight texture. Cement repointing is typically grey, hard, and often with a different profile — a ridge or overhang rather than a flush or slightly recessed finish. Where cement has been applied over terracotta, it often extends slightly onto the face of the terracotta units themselves, which is both unattractive and contributes to water trapping at the joint edge.
Previous poor repairs
Terracotta and faience have a history of attracting poor repair attempts. Cracks and chips filled with ordinary filler, render, or cementitious grout are almost universal on buildings that have received any maintenance attention over the past fifty years. These repairs fail quickly — they are incompatible in movement, colour, and porosity with the original material — and often obscure the extent of the underlying damage.
Paint applied to terracotta is a particular problem. It is sometimes applied to mask staining or repair attempts, and it traps moisture in the porous substrate beneath. Paint removal from terracotta requires careful treatment — chemical strippers at low concentration applied in poultice form, or DOFF at controlled temperature. Abrasive removal is not appropriate.
Cleaning terracotta and faience correctly
The correct starting method for most terracotta and faience cleaning is DOFF: superheated steam at carefully calibrated temperature and low pressure. The steam removes atmospheric soiling and biological growth without contact abrasion and without the high water volumes that would saturate the substrate and potentially drive water behind the glaze of faience units.
The temperature calibration is more critical than with stone. Faience glaze can be affected by thermal shock — rapid heating of a cold, damp surface. The DOFF protocol for glazed surfaces starts at a lower temperature than for stone and increases incrementally through the trial panel. The lance is kept at a greater distance from the surface than for stone cleaning, and dwell time is shorter. The result is slower cleaning but no risk to the glaze integrity.
For stubborn deposits — sulphate crust in sheltered joint recesses, or heavy biological growth in textured unglazed terracotta — a low-concentration chemical biocide can be used as a pre-treatment or follow-up, applied in poultice form and removed rather than rinsed under pressure.
What is not appropriate: pressure washing at any pressure setting, abrasive cleaning methods including TORC (the aggregate is too risky for glazed surfaces), and strong acid or alkali chemical cleaners. The damage done by any of these methods to faience is permanent.
Repair and replacement
Minor chips and cracks in unglazed terracotta can be repaired using a lime-based mortar matched in colour and texture to the original. The repair is not invisible — nothing is truly invisible on terracotta — but a well-matched repair in a compatible material will weather in over time and become progressively less noticeable.
For larger areas of damage, or where structural cracking has compromised a unit's integrity, replacement is the correct approach. Terracotta units can be matched by specialist manufacturers — there are several in the UK who produce to bespoke specifications from mould drawings or surviving units — and new units can be made to the original profile, colour, and firing quality. Lead times for bespoke manufacture are typically eight to twelve weeks.
Faience is more difficult to repair invisibly, because the glaze finish cannot be replicated by any applied repair mortar. Large areas of faience loss on a listed building are typically addressed by replacement rather than patch repair, with the replacement units specified from the same bespoke manufacturers.
The mortar specification for repointing terracotta and faience follows the same logic as for brickwork: lime-based, softer than the surrounding material, matched in colour to the original. The joint profile should replicate the original as closely as possible. On faience, the joint face should be finished flush or very slightly recessed — a proud joint profile would trap water against the glaze edge.
Listed building considerations
Most significant terracotta and faience facades in London are on listed buildings or within conservation areas. Listed Building Consent is required before any cleaning or repair works proceed. The method statement for terracotta and faience work is typically more detailed than for stone or brick, because the risk of damage from incorrect methods is higher and conservation officers scrutinise these applications carefully.
The method statement should address the cleaning method and temperature specification, the trial panel protocol, the mortar specification and matching process, and — where replacement units are required — the procurement route and the intended manufacturer. Historic England guidance on terracotta and faience repair is available and should be referenced in the application.
Common questions
What is the difference between terracotta and faience?
Terracotta is fired clay — unglazed or lightly salt-glazed — used for architectural ornament from the 1870s onwards. Faience is terracotta with a vitreous glaze fired onto the surface, giving it a hard, often highly decorative finish. The glaze makes faience more weather-resistant than unglazed terracotta but also more vulnerable to certain types of cleaning damage.
Can you clean terracotta without damaging it?
Yes, with the right method. DOFF at carefully calibrated temperature is generally the safest approach for both unglazed terracotta and faience. Abrasive methods and high-pressure water are not appropriate — both risk damaging the glaze on faience and the fired surface on unglazed terracotta.
What causes terracotta to crack?
Cracking in terracotta has several causes: thermal expansion, rusting of embedded metal fixings (which expand as they corrode), water ingress through failed joints, and freeze-thaw cycling in areas where water pools. Cement repointing is a common cause of accelerated cracking because it is too rigid to accommodate movement.
Is terracotta on listed buildings difficult to restore?
Terracotta and faience restoration on listed buildings requires Listed Building Consent and, in most cases, consultation with a specialist conservator. The method statement needs to address both the cleaning approach and any repair or replacement specification. We can manage the consent process and prepare the method statement as part of the project.
If you have a terracotta or faience facade that needs assessment, a site visit is the starting point. We will identify the material, assess the condition, and produce a written method statement before any commitment to works.
Request a site visit