Environmental Engineering Reference
In-Depth Information
Figure 8.18.
Scaling linked to gypsum crystallization on the hand of a soft limestone
sculpture in Paris, Louvre, Napoleon Court
When the source of water contaminated by salts is more or less regular, a leaking
pipe for instance, salt related degradation patterns will develop at the limit between
the moist and dry zones of the masonry, and will take an oval shape. If salts are
brought up from the ground by capillary water, the crystallization fringe will be sub-
horizontal and generally located between 0.5 and 1 m. In some instances, a sub-
horizontal crystallization zone may develop several meters above the ground; this
situation may also be due to capillary rise, if salt contamination occurs over a long
time. The progression of the degradation fringe upward is a process not yet really
understood. Two kinds of explanations are proposed [ARN 89]:
- according to the first one, the sequential crystallization of salts, according to
their solubility, leads to the precipitation of salts with very low solubility (such as
calcite) on lower parts of the wall. Calcite precipitation blocks the surface porosity,
and this induces an elevation of the capillary fringe;
- the other explanation is that salts may creep upwards, as they do on laboratory
vessels.
Figure 8.19.
Alveolization on a wall with rising damp,
Saint-Emilion, Gironde, France
