Unlike concrete, well-fired brick doesn't have an internal chemistry that transforms harmfully over time: it doesn't carbonate, it doesn't undergo expansive aggregate reactions, it doesn't lose protective alkalinity because it doesn't need any. Its pathologies are almost always pathologies of water — where it gets in, what it dissolves as it passes through, and what happens when it freezes. Knowing them well is the difference between a brick façade that ages with dignity for a century and one that shows its first defects after the first harsh winter.
Efflorescence: the salt that rises to the surface
Efflorescence consists of whitish, crystalline deposits that appear on the surface of face brick — the most visible defect and the one clients most often flag, even though it's rarely the most serious from a structural standpoint. The mechanism is simple: water present in the brick or mortar, carrying soluble salts (sodium, potassium, magnesium, calcium sulphates), migrates to the surface by capillarity and evaporates. The salts, no longer soluble, crystallize on the surface, leaving that characteristic white deposit. The salts can originate from the starting clay (if it contains calcium carbonate or soluble salts not eliminated by firing), the bedding mortar (Portland cement is a common source of soluble salts), or rising damp from the ground in masonry without an effective horizontal barrier.
Primary efflorescence — the kind that appears in the first months after laying, while the masonry is still releasing its construction moisture — is almost always temporary and washes off with the first rains. Secondary efflorescence, which recurs cyclically for years, indicates a persistent problem: unresolved rising damp, infiltration from poorly detailed roofing or sills, or a mortar with a soluble-salt content too high for that type of brick. Prevention at design stage comes down to three choices: selecting brick with low soluble-salt content (verifiable under EN 771-1), low-salt mortars for face brick, and construction details that prevent water from pooling on sills, cornices and ground-level junctions.
Freeze-thaw: when water in the pores expands
Freeze-thaw is the most serious pathology — not just an aesthetic one — of brick in climates with harsh winters. The mechanism: water penetrates the brick's pores by capillarity or driving rain; when the temperature drops below zero, the water held in the pores freezes and expands in volume by about 9%; if the brick is saturated (full of water, with no free space for expansion) and the freezing is repeated cyclically, the pressure generated spalls the brick's surface — a phenomenon visible as flaking, scale detachment, and progressive loss of material from the exposed surface. A single freeze cycle rarely causes visible damage; it's the dozens of freeze-thaw cycles repeated every winter, for years, that produce the cumulative decay.
A brick's frost resistance isn't an automatic property: it depends on the material's pore structure — a brick with small, well-distributed pores, with enough space for ice to expand into without generating destructive pressures, resists well; a brick with large, interconnected pores, easily saturated, resists poorly. EN 771-1 classifies brick for frost resistance into categories (F0, F1, F2) based precisely on the water-absorption coefficient and behaviour under standardized test cycles. For exposed elements — parapets, copings, sills, cornices in alpine areas or anywhere else subject to many freeze cycles a year — choosing an F2-class brick isn't a technical whim: it's the difference between a detail that lasts decades and one that flakes apart within a few winters.
Sulphate attack: when the problem is in the mortar, not the brick
A third pathology, less well known but not rare, concerns the chemical interaction between sulphates present in the brick (often as natural traces in the clay) and the calcium aluminates in the Portland cement of the bedding mortar. In the presence of persistent moisture, this reaction can form ettringite, a mineral that crystallizes with significant volumetric expansion, capable of fracturing the joint mortar from within. The phenomenon is more frequent in masonry exposed to constant moisture — retaining walls, plinths, masonry in contact with sulphate-rich soils — than in normally ventilated, dry façades. Standard prevention is the use of sulphate-resisting cements (SR class under EN 197-1) in mortars for below-grade masonry or masonry subject to permanent moisture, a precaution that costs very little at design stage and prevents decay that, once it needs fixing, almost always requires demolishing and rebuilding the joint.
The common thread of all three pathologies is that none originates from a defect in the brick itself — they originate from how water is managed in the construction detail. A top-quality brick, laid without a damp-proof course, without a drip below a sill, with a mortar unsuited to the exposure, will still develop efflorescence, freeze-thaw damage or sulphate attack. Diagnosing brick, more than diagnosing other materials, is above all diagnosing water: where it gets in, where it pools, how it evaporates.