Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
Causes of structure and construction climate
The investigations have shown that the main reason obviously is to find in the temporal and local
differences of temperature and humidity within the church. Critical conditions always come up when
warmer air gets to colder surfaces and cools down, followed by an increase of humidity.
Within a church, cold and warm areas are permanent existing, due to frequent heating and cooling
cycles during the heating period, seasonal differences between outdoor and indoor climate (also in
summer time), the large inner volume of a church and the thermal inertia of the building as well.
The organs mostly are separated from the other room of a church, but an air exchange is possible over
lots of active (wind system) and passive (ventilation holes, prospect) openings. Often, the organ wind
is taken from outside or from the roof area
The above described effect may occur even here: warm air from the hall may meet colder areas of the
organ. Additionally, the installation of organs or other objects made of wood close to often not
insulated walls and ceilings may lead to an increased wood moisture.
Use-related causes
Depositions of dust and dirt, resulting from reconstruction work or from a bad cleaning status, may
favour mould infection.
As reported above, a discontinuous heating with short heating and cooling phases, may lead to a
wetting of surfaces and materials.
Also a short increase of the humidity may result in a new infection or a growth phase of an older one.
Thus, at days with higher amount of visitors, additional moisture input is to be expected. As
measurements show, this did not lead stringently to an increase of humidity, caused by the buffering
effect described before.
The churches can be ventilated mostly by opening the doors. To open the windows and crossventilation
is recommended, but often not possible. If a church is ventilated at all, this is done often at
unsuitable climate conditions. This may be the case at summer time, when warm air from outside is
ventilated into the church and meets there cold areas, with risk of condensation (similar mechanism is
known for cellars). With it, the targeted removal of moisture is changed into the opposite. Thus, a
ventilation during summer time should be done only in the cooler morning or evening hours.
Furthermore, during periods of high relative humidity (foggy weather) in spring or autumn, an
intensive ventilation should be avoided.
Use of susceptible materials
Not all materials used for conservation may be infected in the same extend. Some contain nutrients
and thus make mould growth possible even at a lower humidity. Obviously, already some hours with
70 % relative humidity are sufficient to allow mould growth. So, a very strong infection was found at
pre-glued wood surfaces, which were coated with a black casein-tempera, at wooden organ pipes
which were poured with bone glue, as well as at wood, preserved with the oil-based preservative
Hylotox 59 (today forbidden).
Fig. 8: test of biocides for restoring materials (agar diffusion tests)
In the laboratory investigations, following materials used for conservation were found to be
susceptible:
139