Environmental Engineering Reference
In-Depth Information
Chapter 8
Deterioration of Stone in Monuments
8.1 Introduction
In nature, rocks exposed to the weather deteriorate due to exposure to an
environment that is different from that of their diagenesis. This degradation has a
slow rate and leads to the formation of soils, containing minerals in equilibrium with
the new environment [NAH 91]. Some minerals may go through all of the processes
without any change, whereas others are newly formed. For instance, in a granitic
arena, quartz is an unchanged relic of the original granite and kaolinite is a newly-
formed mineral, originating from the degradation of feldspars.
In human constructions, the degradation is often quicker than on natural sites: the
stone is directly exposed to weather, faces more contrasting environmental
conditions, changing at higher rates, and is affected by soluble salt pollution. The
mechanism and degradation rate of monumental stones depends on intrinsic factors,
such as mineralogical composition, pore size distribution, hydric, hygric, thermal
and mechanical properties, and on extrinsic factors, such as water supplies by rain
and/or capillary rise, temperature, nature and quantity of soluble salts in percolating
solutions, and biological factors. The building, through its morphology, determines
the location and intensity of degradation [DEL 89b]: stones will deteriorate
differently if they are directly exposed to rain or sheltered by a cornice. In this
chapter, we will successively study the influence of these various factors. The terms
used to describe the degradation patterns all comply with the definitions of the
