way from those inside a building. The protective effect of protruding roofs or
drainage systems, such as gutters, becomes obvious when, during poor main-
tenance of a building, their function is no longer guaranteed and the walls get
wet. Moreover, the effect of direct sunlight must not be neglected, since, at
different times of the day and the year, these areas may be subject to extreme
variations in temperature.
Wall paintings inside a monument are also subject to climatic influences.
First, the objects on the outer walls are influenced – depending on the thick-
ness and construction of the wall – more or less directly by the climate outside.
This is especially so when the walls are in poor repair, resultingfrom defective
pointing, incomplete outer plaster or sludges. Not only single-hulled walls
but also twin-hulled walls may suffer from an input of moisture, damaging
the paintings inside the monuments. It is obvious, however, that paintings on
inner walls are not usually affected by the climate outside, except perhaps,
through strong illumination by sunlight through windows. Walls on upper
floors are normally not affected by ascending moisture. However, in build-
ings without or with defective damp-proof barrier, rising moisture can be a
serious danger in the lower parts. The accumulation of earth layers around
old churches must be mentioned here. If the soil exceeds the level of the orig-
inal horizontal damp-proof barrier, this barrier loses its effectiveness. This
also takes place in buildings surrounded by rising water level. Depending on
the foundation of the building, the moisture not only reaches the outer walls
but also penetrates further inside as well.
Paintings on ceilings which are not directly situated under the roof are
much less affected by moisture than those situated directly beneath the roof.
Unsuitable heating systems may cause deterioration of such paintings by
condensation, especially if there is no separation between the roof and the
ceiling. More often, water leakages resulting from damaged roofing tiles can
quickly causemassive detrimental effects on ceiling paintings. Paintings
beneath windows are endangered by water not only when old window frames
are leaky, but also when new windows are not fitted correctly or drainage for
condensed water is missing. In situations with reduced ventilation, e.g.behind
altars, large paintings or furniture, humidity may rise too. Last but not least,
wall paintings are damaged during the normal use of the room by mechanical
damage, heating, dust and other pollution.
In addition to mechanical damage, which may be due to extensive use and
may cause a more or less distinct loss of the original paint layer, changes in the
substance of a building deserve consideration. Transfers, very often deliberate,
or unintended, cause damage by whitewashing or plastering. For centuries,
changing styles have caused destruction of wall paintings. New plaster to
carry the“modern painting” may have been applied and the original surface
may have been damaged by holes made to improve the adhesion of the new
242 Chapter 10