Environmental Engineering Reference
In-Depth Information
This adobe structure has a dual socio-cultural heritage from Roman Catholicism
and Nankani-Kassena. Nevertheless, the fragility of the decorations as well as waves
of modernism has led to a decline in the use and technical knowledge of these
traditional techniques.
To repair damage caused to the cathedral and to renew interest in this waning
traditional technique, a program was established between the Getty Grant Program
in Los Angeles and the Center of Research in Earthen Architecture (CRATerre) in
Grenoble.
As the outside bitumen plaster characteristics, including water transport and
storage, may have an influence on the conservation of decorated surfaces inside the
cathedral, one of the aspects of collaboration between the French and American
research institutes was to introduce new research techniques and methodologies in
order to improve earthen surface conservation of the two mediums: bitumen plaster
and decorated surfaces.
11.2.2. Materials and methods
In order to evaluate the physicomechanical properties of the bitumen plaster and
its compatibility with the adobe brick, test mud prisms were made. Materials used in
the field were considered, and an earthen material as close as possible to the original
adobe (in particle size distribution and clay composition) was used for the prisms.
The material for the plaster making came from Navrongo (a mixture of soft sand,
river sand, and the bitumen itself).
The prism size was 10 x 5 x 10 cm and a plaster layer around 1 cm thick was
applied on one face of the prism. Bitumen content used in the field is around 3.5%
mass. Four different concentrations of bitumen, surrounding the field content, were
studied (2%, 3%, 4% and 5%), and their physicomechanical properties compared
with the adobe prism, and plaster support.
Preparation of the plaster followed the procedure observed in the field: soft sand
and river sand were mixed together, and then the boiling bitumen was added until a
thick paste was obtained.
The evaluation methods of the adobe prism, bitumen plaster composition, and
properties were those advised by the RILEM “Recommended tests to measure the
deterioration of stone and to assess the effectiveness of treatment methods” [RIL
80].
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