Masonry/Brickwork

Masonry walls take four main forms, and the form decides what can go wrong. Solid walls, one to two bricks thick and bonded with headers, dominate pre-1930 stock in Britain and Australia and early twentieth-century buildings in the United States. They have no cavity and rely on thickness and soft lime mortar to absorb and release moisture. Cavity walls, two leaves with a gap between them held together by metal ties, became standard in Britain from the 1920s and in Australian multi-storey and commercial work through the mid twentieth century. Brick veneer, a single outer leaf tied back to a timber or steel frame, has been the dominant Australian house and low-rise form since the 1950s. On framed buildings, masonry is cladding: an outer leaf carried at each floor on steel shelf angles or on the slab edge and tied back to the frame.

Bond pattern tells you the form from the street. Header courses (bricks laid end-on, showing their short face, in Flemish or English bond) mean a solid wall. Stretcher bond with no headers means a cavity or veneer, and therefore ties, which are the commonest hidden failure in masonry. Snapped half-bricks laid to imitate headers in stretcher work are a known trap; the rhythm is usually too regular and the heads often look slightly short.

Brick type governs movement. Fired clay bricks expand permanently as they take up moisture after leaving the kiln, quickly in the first months and slowly for decades after. Calcium silicate and concrete bricks and blocks do the opposite and shrink. A wall of either needs movement joints, sized and spaced for its material, and the two must not be mixed in one panel without allowing for the difference. Mortar governs durability. Lime mortar is softer and more permeable than the brick, so the joint weathers and is renewed while the brick survives. Cement mortar is harder and less permeable; laid against soft brick it forces moisture and salts out through the brick face and the brick fails instead of the joint.

What shortens life:

• Exposure. Elevations facing the prevailing rain, sites within a few kilometres of surf, and industrial atmospheres keep walls wetter and consume galvanising faster. The same building can have ties failing on one elevation and sound on another.
• Water management faults. Overflowing gutters, missing copings and sills without drips, blocked weep holes and absent cavity trays put water exactly where ties and lintels sit.
• Missing movement joints. Long runs of clay brick without joints, and brick cladding on concrete frames without soft joints under the shelf angles, crack and bow as the materials move against each other.
• Hard repointing and impermeable coatings. Cement pointing on lime-built walls, and paints or renders that trap moisture, move decay into the brick.
• Bridged damp-proof courses. Raised paths and garden beds, render taken down over the damp-proof course, and debris in the cavity carry ground moisture past the barrier.
• Cavity wall insulation retrofits. Fill injected into cavities in exposed locations can carry rain across to the inner leaf and keep ties wet.

Wall tie corrosion

Ties hold the outer leaf to the inner leaf or frame. Galvanised mild-steel ties lose their zinc once the surrounding mortar carbonates and stays damp, then the steel rusts. Rust occupies several times the volume of the steel it replaces. In the outer leaf bed joint that expansion lifts the brickwork above, and because ties are laid at regular vertical spacing (450 mm in British practice, about every sixth course) the wall cracks horizontally in a regular pattern. Strip ties (fishtail and vertical twist) jack and crack the wall. Wire ties mostly thin and snap with little expansion, so they can lose restraint with no visible sign. The end result in both cases is an outer leaf free to bulge, and under wind suction, to fall.

Lintel and shelf angle corrosion

Steel lintels over openings and shelf angles carrying cladding at each floor corrode where water reaches them, usually because cavity trays and stop ends are missing or weep holes are blocked. Corrosion lifts the brickwork over the lintel and opens a crack along its bearing; as the flange thins the brickwork drops and the opening head deflects. Behind the arches of older buildings, timber lintels rot unseen until the arch drops.

Frame shortening against brick growth

A concrete frame shortens over its first decades through creep and shrinkage. Clay brick grows. Where brick cladding is built tight to the underside of each shelf angle or slab edge, with no compressible joint, the frame unloads onto the brick panel below. The brick at the angle line crushes and spalls, panels bow outward between floors, and corners crack where the two elevations push against each other.

Moisture and thermal movement

Long runs of clay brickwork without movement joints expand and push past corners and returns, producing vertical cracks near corners, cracks at short returns and brickwork sliding outward on the damp-proof course at the base (oversailing). Concrete block and calcium silicate shrink and crack vertically at openings and mid-panel. These cracks are usually even in width and stop growing once the material has stabilised.

Foundation movement

Settlement, subsidence and the seasonal swelling and shrinking of reactive clay soils distort the wall. Cracks run diagonally through brick and mortar, taper (wider at one end), pass through openings, and are accompanied by sticking doors and windows, sloping floors and cracking internally on the same line. On reactive clay they open and close with the seasons; trees, leaking drains and changes to garden watering are the usual triggers.

Sulfate attack

Soluble sulfates from clay bricks, ground water or flue gases react with cement in wet mortar and render, forming expansive compounds. Mortar swells, softens and whitens; the wall grows vertically and cracks along most bed joints, not only at tie courses. Chimneys, parapets, rendered walls and walls in wet ground are the usual places.

Frost and salt damage

Water freezing in saturated brick, and salts crystallising as walls dry, break off brick faces (spalling) and turn surfaces powdery. Salt damage dominates in Australian stock at the base of walls with failed damp-proof courses and in coastal walls; frost damage dominates in Britain and the colder United States in parapets, chimneys and exposed copings. Hard cement pointing concentrates both in the brick.

Damp

Rising damp is ground moisture drawn up a wall without a working damp-proof course, carrying salts that deposit in a band up to about a metre high. Penetrating damp is rain driven through solid walls, defective pointing, or across a cavity bridged by mortar droppings, debris on ties or retrofit insulation. Both decay plaster, timber in contact with the wall, and embedded steel.

Rust jacking of embedded steel

In early steel-framed buildings the columns and spandrel beams are wrapped in solid masonry with no drainage. Water reaching the steel rusts it, and the rust pushes the masonry outward along column and floor lines, cracking corners and displacing brick and stone, often first at parapets where exposure is greatest.

From the street and from aerial imagery

• Horizontal cracks at regular vertical spacing across an elevation; on a veneer or cavity wall this is the tie signature.
• Bulging or bowing panels, best seen by sighting along the wall at a low angle or in raking light; floor-line bowing on framed buildings.
• Brickwork lifted at eaves or verges, or a gap opening under the roof edge.
• Stepped cracks rising from the ends of lintels, rust staining below lintels and shelf angles, dropped arches.
• Diagonal tapering cracks through openings; distorted window heads.
• Spalled brick faces, mortar eroded or proud of the brick, mismatched patch repairs and repointing in a different colour.
• Vegetation in joints, overflowing gutter staining, white salt deposits and lime runs below defective details.
• Weep holes buried by paving or garden beds; render carried down over the damp-proof course.

Close up on site

• Mortar that is soft enough to rake out with a key or crumbles to the touch; white, swollen mortar in most joints (sulfate).
• Hollow sound or movement when brick faces are tapped; loose bricks at parapets and corners.
• Crack width and whether it tapers; whether the crack passes through bricks or follows joints; displacement across the crack face.
• Rust at lintel bearings, compressed or missing sealant under shelf angles, spalling along the angle line.
• A salt tide line and eroded brick just above ground; damp-proof course visible or bridged.

Inside the building

• Damp, blown plaster and salt bloom on the inside face of external walls, highest at the base (rising) or random and weather-related (penetrating).
• Cracks on the internal face on the same line as external cracks: this points to movement of the whole wall, not only the outer leaf.
• Sticking doors and windows, floor slopes and cornice gaps on the same line as external cracking: foundation movement.
• Decayed skirting and floor timbers against external walls.

In the records

• Repeated repointing or crack repair on the same elevation, which means the cause was never addressed.
• Leak logs concentrated on one elevation, at window heads, or at each floor line.
• Previous façade inspections with unsafe or safe-with-repairs findings, and make-safe hoarding or netting invoices.
• Original specifications naming the tie type and lintel material; an absent tie specification on a building of the right era.

Most masonry defects show as cracks, and the pattern of the crack identifies the cause far more reliably than its width. Read the pattern first, then the width.

Two patterns are often confused. Tie cracking and sulfate cracking are both horizontal: tie cracks repeat only at tie courses and only in the outer leaf; sulfate cracks appear in most joints and the mortar itself is changed. Foundation cracks and movement cracks can both start at openings: foundation cracks taper and distort the opening; movement cracks are even and leave it square.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator, ordinance or order sets the date, as façade inspection ordinances do), check (investigate before sizing works) and nil (cosmetic or stable).

Crack width scales are a useful second step. The BRE Digest 251 scale in Britain and the masonry damage categories in Appendix C of AS 2870 in Australia both grade damage by width: category 0 under 0.1 mm, 1 up to 1 mm, 2 up to 5 mm, 3 from 5 to 15 mm, 4 from 15 to 25 mm, with BRE adding 5 above 25 mm. Category 0 to 1 is normally cosmetic, 2 is moderate and usually repairable, 3 and above indicates significant movement needing structural attention.

A building surveyor leads the survey; a structural engineer joins where there is bulging, lean or suspected foundation movement; a façade engineer leads on framed buildings and on buildings under a façade ordinance. In New York the inspection must be made by a Qualified Exterior Wall Inspector.

• Visual survey of every elevation, close up from access where defects or public areas warrant it, with a crack map recording location, pattern, width and taper.
• Tie inspection. Locate ties with a metal detector, drill and inspect by borescope, and remove a brick or tie at representative positions to examine the embedded section, where corrosion is worst. Weight sampling to the most exposed elevations and upper storeys; extend it when corrosion is found. BRE Digest 401 sets out the approach in British practice.
• Mortar analysis where sulfate attack is suspected, or to specify matching repointing mortar.
• Plumb and bulge survey by laser or plumb line where panels look out of line; record for comparison.
• Crack monitoring with tell-tales or gauge studs for at least twelve months, covering a full wet and dry season on reactive clay, before concluding a crack is stable.
• Lintels and shelf angles: covermeter to locate, opening up at bearings to see section loss and tray detail.
• Hammer tapping of faces and parapets over public areas, removing anything loose at the time.
• Moisture: calcium carbide or gravimetric samples at depth. Electrical moisture meters read salt as water and overstate rising damp; they show distribution, not diagnosis.
• Thermography to show wet zones, cavity fill voids and bridged areas.

The report should state the form of wall, the tie type and condition by elevation and height, lintel and shelf angle condition, crack causes with the evidence for each, anything made safe, and repairs by priority with extents measured, not estimated.

• Remedial ties. Stainless helical or resin-anchored ties drilled through the outer leaf into the inner leaf or frame, at the spacing the standard requires, with extra ties at openings, corners and the top of walls. Strip ties that are expanding must be removed or cut back from the outer leaf, or the jacking continues; wire ties can usually be left in place.
• Rebuilding. Panels bulged beyond what ties can restrain, or with bricks displaced, are taken down and rebuilt on new ties.
• Lintels. Replace in stainless steel or galvanised to the exposure class, with a cavity tray, stop ends and weep holes over; prop the brickwork above during the work.
• Shelf angles and floor lines. Cut out the mortar bed beneath each angle and form a soft joint of compressible filler and sealant; inspect and treat the angle and its fixings; where angles have lost section, replace them, which requires propping the cladding.
• Movement joints. Saw-cut and seal joints at corners and in long runs; tie across where panels have been freed.
• Repointing. Rake out to a depth of about twice the joint width, and repoint in a mortar no stronger than the brick; lime mortar for lime-built walls.
• Damp. Remove the bridging first (lower ground and paving, cut render back above the damp-proof course, clear debris from cavities); then a new damp-proof course where the old one has failed, sawn-in or injected; replaster internally in salt-resistant systems.
• Embedded steel. Open up along the affected lines, clean or replace and protect the steel, and rebuild with flashing and drainage the original lacked.
• Foundation movement. Address the cause (drains, trees, watering) and monitor; underpinning is reserved for movement that continues after the cause is removed.

Interactions: tie and lintel work, repointing and shelf angle joints share the same access and are best packaged by elevation; cavity insulation may need to be extracted where it bridges; older renders and paints may hold hazardous materials that set the method.

Investigation is a lump sum with a rate for each probe or opening. Remedial ties and repointing are measured by wall area; lintels by opening; soft joints, damp-proof courses and movement joints by linear metre; rebuilding by area. Access is often the largest single component on multi-storey façades, which is why works are packaged elevation by elevation. Make-safe protection recurs until the repair is done.

The usual register shape is two-part: the investigation as a check line, and a conditional works envelope sized from what it finds. Ties, lintels and shelf angles are lifecycle items; repointing is repairs and maintenance on a long cycle; ordinance inspections and make-safe works are code compliance.

• Australia. The National Construction Code calls up AS 3700 Masonry structures and AS 4773 Masonry for small buildings; wall ties are rated to exposure classes under AS/NZS 2699.1, and masonry units are tested to AS/NZS 4456. AS 2870 governs residential footings and gives the crack damage categories. There is no periodic façade inspection regime; on strata buildings the façade is common property and belongs in the capital works plan.
• United Kingdom. Approved Documents A and C set structural and moisture requirements; design follows BS EN 1996 with PD 6697 guidance on movement joints, workmanship BS 8000-3, and cleaning and repair BS 8221-1 and BS 8221-2. BRE Digests 251 (crack classification) and 401 (replacing wall ties) are the working references. On leasehold blocks the works are service-charge items subject to section 20 consultation; higher-risk buildings sit under the Building Safety Act 2022.
• United States. The International Building Code calls up TMS 402/602 for masonry; ASTM E2270 sets the practice for periodic façade inspection. New York City's Façade Inspection and Safety Program requires a critical examination of buildings over six storeys every five years, with Cycle 10 filing windows running from February 2025 to February 2029 across three sub-cycles; Chicago, Boston, San Francisco and several other cities run comparable ordinances. The Brick Industry Association's Technical Notes are the standard practice references for ties, movement and repair.

• Previous façade inspection reports and any ordinance filings, with their unsafe and repair findings.
• Drawings and specifications showing the wall form, tie type, lintels and shelf angles.
• Records of tie replacement, lintel replacement, repointing and crack repairs, with dates, extents and warranties.
• Any crack monitoring data and engineer's reports on movement or foundations.
• Damp-proof course installation records and guarantees, and any cavity insulation retrofit records.
• Leak and damp logs by elevation, and make-safe hoarding or netting records.
• Heritage listing and conservation constraints, which set materials and methods.