The Physics of Water Transfer in Stone - Environmental Geomechanics - page 242

precisely imbibition or capillary rises − when the water globally moves upwards
from the bottom to the top of a wall, for instance. The limit, often visible, between
the wetted lower part of that wall ( capillary fringe ) and the upper part that
apparently stays “dry” reveals the wetting front position. The zone where this
wetting front fluctuates under the combined influences of the intensity of water
sources and local drying conditions is the zone where salts dissolve or precipitate
forming efflorescences that can be observed at the wall surface (see the example in
Figure 9.1). Capillary rise is often associated with water in the basement and/or in
surrounding soil, but not always. Water can also originate from non-permanent run-
off or driving rain (see next section).
Figure 9.1. Example of a zone affected by capillary rises at the bottom of a wall.
Montsoreau castle, “tuffeau” stone [DES 95]
9.1.1.2. Rain
Under the combined effects or rain and wind, the outer parts of a building can
directly receive water. This is called driving rain . Of course, this water can infiltrate
the masonry by the same mechanism (see section 9.3.4) that drives capillary rises.
Nevertheless, driving rain differs from capillary rises in three main ways:
- water supply from driving rain is basically an intermittent phenomenon;