Defect Atlas — Ceramics & Terracotta

Very fine cracks through the ceramic body, often visible only on close inspection or in raking light.

Thin linear marks following or crossing the form; may extend through glaze and body or be confined to one layer.

Drying and firing stresses, thermal cycling, sustained loading or minor impact may contribute.

• location, length and orientation of cracks
• whether cracks pass through glaze, body or both
• association with edges, fixings or stress points
• any indication of recent change

“Hairline cracking was recorded across the upper face of the unit, extending through glaze and into the body.”

Cracks of sufficient width to admit moisture, debris or vegetation, with potential for progressive damage.

Linear openings of varying width; sometimes with associated soiling, biological growth or salt accumulation within the crack.

Continuing movement, frost action, sustained loading or past impact may contribute.

• width, length and orientation of cracks
• any deposits or growth within the crack
• evidence of progression
• association with surrounding joints or fixings

“Open cracking was recorded across the cornice unit, with associated soiling and minor vegetation within the crack line.”

Full break through a ceramic unit, with separated or displaced fragments.

Discontinuity through the unit; visible separation; sometimes with associated displacement or loss of fragments.

Impact, structural movement, frost or accumulated stress may contribute.

• location and orientation of fracture
• presence and stability of all fragments
• any associated displacement
• evidence of past repair

“A fracture was recorded through the lower section, with the detached fragment in place but unsecured.”

Breakage with a pattern consistent with a localised impact event.

Radial or concentric fracture patterns; localised loss; sometimes with associated damage to adjacent units.

Past impact, handling damage or accidental contact may contribute.

• location and pattern of breakage
• extent of associated loss
• evidence of recent or historic origin
• stability of surrounding material

“Impact breakage was recorded in the lower right of the panel, with a radial fracture pattern and associated edge loss.”

Radiating cracks emanating from a point, sometimes associated with fixings or impact.

Multiple cracks radiating from a central point; sometimes with associated surface loss at the centre.

Localised stress at fixings, sustained point loading or past impact may contribute.

• location of central point
• number, length and orientation of radiating cracks
• association with fixings or services
• evidence of progression

“Star cracking was recorded around a metal fixing in the upper section of the unit.”

Localised loss of material along the edge of a ceramic unit.

Irregular notches or losses along edges; sometimes exposing differently coloured body beneath glaze.

Handling, impact, frost or edge stress may contribute.

• location, size and depth of chips
• whether chips expose body or remain within glaze
• evidence of recent or historic origin
• stability of surrounding edge

“Edge chips were recorded along the lower arris of the unit, exposing the underlying body in several places.”

Loss of material at the corner of a ceramic unit, often more extensive than an edge chip.

Missing corner section; sometimes with exposed body and irregular fracture surfaces.

Impact, frost action, handling or accumulated stress may contribute.

• location and extent of corner loss
• any retained detached fragments
• stability of surrounding material
• evidence of past repair

“Corner loss of approximately 40 mm was recorded at the lower left of the unit, with the detached fragment not present.”

Loss of fragments from the surface of the ceramic body, generally parallel to the face.

Saucer-shaped or laminar losses revealing fresher material beneath; sometimes with loose fragments still in place.

Frost action, salt crystallisation, moisture cycling or manufacturing weaknesses may contribute.

• location, extent and depth of spalling
• association with moisture pathways or fixings
• stability of remaining surface
• any retained loose fragments

“Spalling was recorded across the face of the unit, with shallow losses revealing the underlying body.”

Generalised wearing of the ceramic or glazed surface, often at handling or traffic points.

Thinned glaze, dulled surface, loss of fine detail; sometimes localised to wear paths.

Foot or hand traffic, cleaning, weathering or past intervention may contribute.

• location and extent of abrasion
• association with traffic or handling patterns
• loss of original detail
• stability of remaining surface

“Surface abrasion was recorded across the central tile, with loss of glaze sheen along the traffic path.”

Loss of cohesion at the ceramic surface producing a powdery or friable layer.

Surface that readily releases fine material on light contact; sometimes with associated colour change.

Salt activity, severe weathering, fire damage or under-fired body may contribute.

• extent of powdering
• behaviour under minimal contact
• associated staining or salt evidence
• stability under environmental conditions

“A powdering surface was recorded across the lower section, releasing fine material on light contact.”

Generalised weakening of the terracotta body, with reduced cohesion and surface integrity.

Soft, crumbly body; loss of surface to light pressure; sometimes with associated salt activity or moisture indicators.

Severe weathering, salt cycling, under-firing or moisture exposure may contribute.

• extent and distribution of friability
• associated moisture or salt evidence
• stability of architectural function
• evidence of progression

“Friable terracotta was recorded across the cornice, with body material releasing readily under light pressure.”

Separation of layers within the ceramic body or between body and applied surface, parallel to the face.

Lifting of surface layers; visible voids beneath; sometimes with audible drumminess.

Manufacturing lamination, moisture cycling, frost or salt activity may contribute.

• location and extent of delamination
• stability of lifting layers
• presence of drumminess on light tapping
• evidence of moisture pathways

“Delamination was recorded across the face of the unit, with audible drumminess across approximately a third of the surface.”

Erosion or breakage of moulded or applied relief decoration, with loss of original sculptural detail.

Worn, rounded or broken relief; missing applied elements; sometimes with associated soiling in the remaining hollows.

Weathering, abrasion, frost, salt activity or past impact may contribute.

• extent of loss
• comparison with surviving comparable units
• stability of remaining relief
• evidence of past repair

“Loss of decorative relief was recorded across the upper face, with the original moulded foliage now substantially worn.”

Erosion or loss of inscribed, incised or fine surface detail, with reduction of historical legibility.

Faint, partial or absent inscriptions; loss of incised lines; reduced contrast of surviving detail.

Weathering, abrasion, past cleaning or surface loss may contribute.

• current legibility of inscriptions or detail
• areas of greatest loss
• comparison with documented historical records
• any associated surface loss

“Loss of inscription was recorded across the lower band, with several characters no longer legible from normal viewing distance.”

Network of fine cracks confined to the glaze layer, with the underlying body generally intact.

Fine, often interconnected cracks across the glaze; sometimes with associated soiling within the network.

Differential thermal or moisture expansion between glaze and body, age or original firing may contribute.

• extent and pattern of crazing
• any associated soiling or staining within the network
• evidence of glaze loss along crazing lines
• comparison between exposed and protected areas

“Glaze crazing was recorded across the surface of the tile, with associated darkening along the crack network.”

Localised lifting or loss of the glaze layer from the body beneath.

Detached flakes of glaze; small voids revealing the body beneath; sometimes with loose fragments retained on the surface.

Loss of adhesion between glaze and body, differential movement or moisture activity may contribute.

• location and extent of flaking
• size of detaching or detached flakes
• stability of remaining glaze
• any retained loose fragments

“Glaze flaking was recorded across the upper face of the unit, with several flakes loose or recently detached.”

Areas where the glaze has been lost from the body, exposing the underlying material.

Discrete voids in the glaze surface; sometimes with associated abrasion, staining or body weathering.

Cumulative weathering, frost, salt activity, mechanical damage or past flaking may contribute.

• extent and distribution of glaze loss
• condition of exposed body
• stability of remaining glaze edges
• evidence of progression

“Glaze loss was recorded across approximately a quarter of the tile face, with the underlying body exposed.”

Raised, hollow blisters within the glaze surface, sometimes intact and sometimes burst.

Domed blisters of varying size; sometimes burst, leaving crater-like voids; may be original manufacturing features or weathering-related.

Original firing, trapped gases, moisture activity or salt crystallisation may contribute.

• size, distribution and condition of blisters
• evidence of recent versus original origin
• stability of intact blisters
• associated glaze or body loss

“Glaze blistering was recorded across the face of the unit, with several intact blisters and a small number burst.”

Discolouration of the glaze, often associated with crazing, soiling or chemical interaction.

Localised or generalised darkening, yellowing or coloured staining within the glaze layer.

Soiling ingress through crazing, metal run-off or chemical interaction with deposits may contribute.

• extent and colour of staining
• association with crazing or run-off pathways
• evidence of past cleaning
• stability of the glaze in stained areas

“Glaze staining was recorded across the lower section of the tile, with darkening associated with the existing craze network.”

Accumulated deposits on the glazed surface that obscure or interact with the original finish.

Localised crusts, films or layered deposits; sometimes adherent and sometimes loose.

Atmospheric pollutants, run-off from adjacent materials or past treatments may contribute.

• location and extent of accretions
• adherence to the surface
• evidence of underlying glaze damage
• any record of past cleaning attempts

“Surface accretions were recorded across the lower band of tiles, with grey crusts adherent to the glazed surface.”

Loss of an applied slip or engobe layer between body and glaze, with associated effects on appearance.

Patchy colour change; localised glaze instability; differences in body colour beneath glaze losses.

Differential movement between layers, moisture activity or original adhesion issues may contribute.

• extent and location of loss
• associated glaze or body damage
• stability of remaining layers
• evidence of progression

“Loss of slip was recorded across an area approximately 50 mm square, with associated glaze instability.”

Visible salt crystallisation on the ceramic surface as moisture evaporates.

White or pale crystalline deposits on the surface; sometimes fluffy, sometimes hard; may be transient with environmental conditions.

Moisture transport through the body carrying soluble salts may contribute; salt source identification requires analysis.

• extent and distribution of efflorescence
• association with moisture pathways
• appearance under different environmental conditions
• evidence of progressive surface loss in affected areas

“Salt efflorescence was recorded across the lower section of the wall, varying in extent with recent weather conditions.”

Salt crystallisation occurring below the ceramic surface, with potential for spalling or surface loss.

Visible surface disruption, blistering or flaking without surface salt deposits; sometimes with associated whitish bloom.

Moisture transport with salts and evaporation within the body may contribute; identification requires analysis.

• evidence of surface disruption without visible salts
• location relative to moisture pathways
• associated body damage
• evidence of progression

“Possible subflorescence damage was recorded across the face of the unit, with surface flaking and no visible salt accumulation.”

Discolouration of the ceramic surface associated with current or past moisture exposure.

Darkened areas, sometimes following moisture pathways; tide marks at boundaries; differential drying after rain.

Rainwater ingress, rising moisture, condensation or leaks may contribute.

• location and extent of damp staining
• association with identifiable moisture sources
• presence of tide marks
• evidence of associated salt activity

“Damp staining was recorded across the lower section, with a defined tide mark approximately 500 mm above ground level.”

Linear or fan-shaped staining produced by repeated run-off across the ceramic surface.

Streaks or fans of darker material following run-off pathways below ledges, sills, gutters or projections.

Concentrated rainwater run-off carrying soiling or dissolved material may contribute.

• pathways of run-off
• association with overhead features
• extent and intensity of staining
• evidence of associated surface loss

“Water run-off staining was recorded below the projecting cornice, with linear streaks descending across the face.”

Orange to brown staining of the ceramic surface from iron migration, typically from fixings, reinforcement or inclusions.

Discrete rust-coloured marks at fixings or inclusions; broader staining where iron has migrated through the body.

Corrosion of embedded ferrous fixings, reinforcement or original inclusions in the body may contribute.

• location and pattern of staining
• association with visible or buried fixings
• evidence of associated cracking
• extent of migration

“Iron staining was recorded across the face, radiating from a corroded embedded fixing in the upper section.”

Green to blue-green staining from copper or copper-alloy run-off, typically from roof flashings, fixings or downpipes.

Streaks, fans or localised areas of green to blue-green staining; often associated with run-off pathways.

Run-off from copper, brass or bronze elements may contribute.

• location and pattern of staining
• association with copper-alloy elements
• extent of run-off pathway affected
• evidence of associated surface damage

“Copper staining was recorded below the rainwater hopper, with green streaks descending across the face.”

Generalised darkening of the ceramic surface from accumulated atmospheric particulates.

Even or patterned grey to black soiling, often heaviest on rain-protected surfaces.

Cumulative deposition of atmospheric particulates may contribute.

• extent and pattern of soiling
• comparison between rain-washed and protected surfaces
• evidence of past cleaning
• interaction with underlying surface

“Atmospheric soiling was recorded across the protected surfaces of the cornice, with rain-washed areas notably cleaner.”

Hard, dark crustal deposits associated with sulphation and atmospheric pollutants on rain-protected surfaces.

Thick, hard, black or dark grey crusts; often raised above the original surface; sometimes incorporating particulates.

Sulphation reactions with calcareous material in glaze, body or mortar and atmospheric pollutants may contribute.

• extent and thickness of crusts
• location on rain-protected versus washed surfaces
• evidence of loss beneath crusts
• stability and adherence of crust

“Black crusts were recorded on the underside of the projecting unit, with associated surface loss visible at crust edges.”

Staining of the ceramic surface by mortar run-off, residues from past pointing or repointing.

Pale, calcareous staining around joints; runs descending from mortar lines; localised concretions on the surface.

Mortar washout, recent repointing or surplus mortar may contribute.

• extent and pattern of staining
• association with current or recent works
• evidence of mortar smears or residues
• stability of surface beneath staining

“Mortar staining was recorded across the units adjacent to recently repointed joints, with pale runs descending across the face.”

Adherent deposits not directly attributable to a single source, including biological residues, dirt films and minor concretions.

Patchy or generalised adherent material on the surface; varying colour and texture.

Cumulative environmental exposure and past surface interactions may contribute.

• type and distribution of accretions
• adherence to the surface
• evidence of underlying damage
• any record of past cleaning

“Surface accretions were recorded across the lower section, with patchy adherent deposits of mixed character.”

A ceramic unit that has moved from its original position within the assembly.

Misalignment with surrounding units; projection or recession from the original face; sometimes with open joints.

Structural movement, bedding failure, frost, fixing failure or past intervention may contribute.

• direction and extent of displacement
• associated open joints
• stability of current position
• evidence of recent or longstanding origin

“A displaced unit was recorded in the upper course, projecting approximately 8 mm from the surrounding face.”

A ceramic unit that is no longer securely held in place, with potential for further movement or loss.

Movement under light pressure; open joints; sometimes with audible looseness on tapping.

Bedding failure, fixing corrosion, frost or moisture activity may contribute.

• extent of movement
• condition of bedding and fixings
• evidence of associated cracking
• risk of fall or further movement

“A loose unit was recorded in the upper section, moving under light hand pressure.”

A glazed tile that has lost adhesion to its substrate, with potential to detach.

Drummy sound under light tapping; visible lifting; sometimes with open edges around the tile.

Adhesive failure, moisture activity, substrate movement or freeze–thaw cycling may contribute.

• location and number of loose tiles
• drumminess on light tapping
• evidence of moisture pathways
• risk of detachment

“Several loose tiles were recorded across the lower band, with drumminess audible on light tapping.”

Joints between ceramic units that have lost their original fill, allowing moisture or debris ingress.

Visible gaps along joint lines; loss of mortar or grout; sometimes with associated soiling or vegetation.

Mortar weathering, movement, frost or past intervention may contribute.

• location, width and length of open joints
• extent of remaining fill
• evidence of moisture ingress
• association with displaced units

“Open joints were recorded across the central panel, with mortar lost to depths of up to 10 mm in places.”

Mortar pointing that has cracked, detached or lost integrity within the joints.

Cracked, loose or missing pointing; sometimes with associated unit damage; visible voids.

Mortar weathering, movement, incompatible repointing or frost may contribute.

• extent and pattern of failure
• type of mortar where assessable
• association with unit damage
• evidence of past repointing campaigns

“Failed pointing was recorded across the wall, with cement-based mortar cracked and partially detached from adjacent units.”

A ceramic unit lost from its original position, leaving a void within the assembly.

Empty bedding pocket; sometimes with retained adhesive, substrate damage or moisture ingress.

Past loss, failure of fixings or bedding, or removal during intervention may contribute.

• location and size of voids
• condition of surrounding units
• evidence of substrate damage
• presence of fragments locally

“A missing unit was recorded in the lower course, with the bedding pocket and exposed substrate visible.”

Generalised biological colonisation of the ceramic surface, including algae, fungi and mixed growths.

Green, black or pink tinting of the surface; sometimes patchy, sometimes generalised; varying with moisture and orientation.

Sustained moisture, shading and surface microtopography may contribute.

• extent and colour of growth
• association with moisture pathways or shading
• evidence of interaction with surface
• stability of underlying material

“Biological growth was recorded across the lower section, with green and black tinting on shaded faces.”

Lichen growth on the ceramic surface, varying from minor crustose colonies to extensive cover.

Discrete or coalescing lichen colonies of varying form, colour and adherence; sometimes with associated surface alteration.

Surface texture, environmental exposure and slow long-term colonisation may contribute.

• extent, type and adherence of colonies
• evidence of associated surface change
• value as long-established growth
• current stability of surface beneath

“Lichen colonisation was recorded across the upper face, with several well-established colonies firmly adherent.”

Moss growth in joints, hollows or sheltered areas of the ceramic surface.

Cushions or mats of moss in joints, voids or sheltered areas; often associated with retained moisture.

Sustained moisture retention, organic debris and shade may contribute.

• location and extent of moss
• association with moisture retention
• evidence of joint or surface damage beneath
• interaction with adjacent vegetation

“Moss growth was recorded along the open joints of the lower courses, with sustained moisture in the affected area.”

Establishment of higher plants in joints, cracks or accumulated debris.

Seedlings, established small plants or larger vegetation rooted in joints or losses; sometimes with associated mechanical damage.

Open joints, accumulated debris and seed deposition may contribute.

• type, location and size of plants
• evidence of root penetration
• associated joint or unit damage
• risk of progressive damage if left in place

“Higher plant growth was recorded along the upper joints, with seedlings establishing in accumulated debris.”

Repair using cementitious materials that are mechanically or physically incompatible with the historic ceramic body.

Hard, dense, often grey infills or patches; sometimes with associated cracking, spalling or moisture damage to adjacent original material.

Past repair using inappropriate materials may contribute.

• extent and location of cement repairs
• evidence of damage to adjacent original material
• stability and adherence of the repair
• evidence of moisture trapping

“Inappropriate cement repair was recorded across the lower section, with associated spalling of adjacent original terracotta.”

Pointing or bedding mortar that is materially incompatible with the original ceramic and surrounding fabric.

Hard, dense or unusually coloured mortar in joints; sometimes with associated unit damage at joint edges.

Past repointing with inappropriate mortars may contribute.

• extent of incompatible mortar
• evidence of damage to adjacent units
• comparison with surviving original mortar
• stability of the mortar itself

“Incompatible mortar was recorded across the wall, with hard, dense pointing and associated edge damage to adjacent units.”

Earlier repairs using adhesives to rejoin fragments or stabilise loose material.

Visible glue lines, residues or fills; sometimes discoloured; variable adhesion.

Past repair campaigns of varying material and skill may contribute.

• location and method of adhesive repair
• current adhesion and stability
• evidence of staining or migration
• compatibility with the original material

“A previous adhesive repair was recorded across the fracture in the upper section, with visible discoloured residue along the join.”

Paint applied over the original ceramic or glazed surface, obscuring or altering its appearance.

Modern paint film across original surfaces; sometimes flaking, sometimes intact; variable colour and adhesion.

Past redecoration or attempts to disguise damage may contribute.

• extent and adhesion of overpaint
• evidence of damage beneath
• stability of the paint film
• any record of original appearance

“Overpaint was recorded across the lower band, partially obscuring the original glaze and now flaking in places.”

Failure of a previously applied coating, whether protective or decorative.

Flaking, peeling or discoloured coating; sometimes with associated damage to the surface beneath; differential weathering.

Coating age, environmental exposure or incompatibility with the substrate may contribute.

• type and extent of coating
• pattern and extent of failure
• condition of surface beneath
• evidence of past recoating

“Coating failure was recorded across the face of the unit, with peeling consistent with extended exposure since last application.”

A replacement ceramic unit or repair element that is failing or behaving differently from original material.

Replacement units showing accelerated weathering, differential staining or premature loss compared with original surrounding material.

Material incompatibility, manufacturing differences or installation issues may contribute.

• identification of replacement units
• comparison of weathering with originals
• evidence of accelerated failure
• stability within the assembly

“A failed replacement unit was recorded in the upper course, weathering significantly faster than surrounding original material.”

Corroded, broken or otherwise compromised fixings used to secure ceramic units.

Visible corrosion at fixings; staining, cracking or displacement around fixing positions; sometimes with associated unit loss.

Corrosion of ferrous fixings, mechanical failure or moisture ingress may contribute.

• location and condition of visible fixings
• evidence of staining or cracking around fixings
• stability of associated units
• extent across the assembly

“Failed fixings were recorded across the upper section, with associated iron staining and localised cracking around the fixing points.”

Loss of integrity within the bedding mortar or material supporting ceramic units.

Voids beneath units; settlement; movement under load; sometimes with associated cracking.

Mortar weathering, moisture activity, frost or original construction may contribute.

• extent and location of bedding failure
• evidence of unit movement
• associated cracking or open joints
• stability of the assembly

“Failed bedding was recorded beneath the central units, with visible voids and minor settlement.”

A ceramic unit projecting beyond its current support, with potential structural risk.

Visible overhang; associated cracking; sometimes with progressive movement.

Loss of underlying support, displacement of adjacent units or original construction may contribute.

• extent of unsupported projection
• associated cracking or movement
• stability under load
• evidence of progression

“An unsupported overhang was recorded in the cornice, with associated cracking and minor movement under light pressure.”

Damage associated with the installation of services through, around or behind ceramic assemblies.

Drilled, cut or broken units; surface losses; sometimes with poorly made-good infills.

Past service installations and unsympathetic making-good may contribute.

• location and extent of damage
• type and method of service penetration
• stability of surrounding material
• quality of any made-good repairs

“Service penetration damage was recorded across several units, with drilled holes and unsympathetic cement infill.”

Loss of surface material from the ceramic body associated with freeze–thaw cycling of retained moisture.

Spalling, surface flaking or laminar losses, often concentrated on wet, exposed or north-facing surfaces.

Moisture saturation followed by freezing cycles may contribute.

• extent and distribution of losses
• association with moisture pathways and orientation
• comparison between exposed and sheltered surfaces
• evidence of progression

“Frost-related surface loss was recorded across the lower north-facing section, with shallow spalling concentrated below the splash zone.”

Damage to ceramic material from past exposure to fire or extreme heat.

Discolouration, blackening, glaze alteration, cracking or spalling consistent with thermal exposure; sometimes with associated soot deposits.

Past fire events or proximity to extreme heat may contribute.

• extent and pattern of damage
• associated soot or thermal indicators
• stability of affected material
• any record of past fire events

“Fire damage was recorded across the upper section, with blackening, glaze alteration and associated cracking consistent with past thermal exposure.”

Original manufacturing features — inclusions, voids, lamination weaknesses — that have become significant during the life of the unit.

Visible inclusions, internal voids, irregular firing, surface defects or laminar weaknesses associated with original production.

Original manufacturing conditions may contribute; environmental cycling can reveal latent flaws over time.

• type and extent of manufacturing flaws
• evidence of associated in-service damage
• comparison with other units in the assembly
• stability of the affected unit

“A manufacturing flaw was visible across the face of the unit, with a lamination weakness now associated with progressive surface loss.”

Departure from the original geometry of a ceramic unit, often an original firing characteristic but sometimes service-related.

Bowed, twisted or distorted units; out-of-plane faces; sometimes with associated stress on adjacent units.

Original firing, sustained loading, thermal cycling or substrate movement may contribute.

• type and magnitude of deformation
• evidence of original versus in-service origin
• associated stress or damage in surrounding material
• stability within the assembly

“Deformation was recorded across the unit, with approximately 4 mm of bow visible against a straight edge.”

Damage from past impact events, including chips, cracks, fractures and localised loss.

Localised chips, cracks or losses with patterns consistent with a discrete impact; sometimes with associated displacement.

Past handling, accidental contact or other impact events may contribute.

• location, extent and pattern of damage
• evidence of recent or historic origin
• stability of surrounding material
• any retained detached fragments

“Impact damage was recorded in the lower right of the panel, with associated chips and a short radial crack.”

Damage arising from past or recent handling, including edge chips, abrasion and stress cracking.

Damage concentrated at handling points; edge chips; localised abrasion; sometimes with associated cracking.

Past or recent handling, transport or display arrangements may contribute.

• location and type of damage
• association with handling points
• evidence of recent or historic origin
• stability of affected areas

“Handling damage was recorded along the edges of the moveable unit, with chips and localised abrasion at lifting points.”