Introduction to Part I

In most artefacts a crack indicates that the item has failed – or will do so shortly, no matter whether that item is a turbine blade or a teacup handle – and that urgent repair or replacement is essential.

Cracking in buildings does not follow this general conception. The total collapse of a building may indeed be preceded by an observable, apparently innocuous hairline crack in its fabric; but total or even partial collapse of a building within its expected service life is fortunately rare indeed, barring acts of war, earthquake and similar catastrophic events.

Virtually all parts of buildings are subjected to continuing size changes, expanding or perhaps contracting as the materials used in their construction respond to changes in temperature or moisture content. Buildings are comparatively large, complex and rigid structures, constructed from disparate materials with component parts subjected simultaneously to differing environmental conditions. It is not surprising that cracks are inevitable, though only some impair the serviceability of a building or may do so if they widen further. (Appendix A presents a method of classifying visible damage to walls.) Such cracks may justify repair or require measures to ensure that they do not develop further. Distinguishing these from the remainder, the vast majority, requires an adequate understanding of the various factors involved: the materials technology, the causes, the mechanisms and the performance consequences of cracks. To that extent, one of the aims of this book is to discourage any automatic assumption that a crack is necessarily significant – diminishing the building’s integrity and worth, and demanding urgent remedy – and to substitute overreaction with calm and reasoned appraisal based on sound knowledge.