Environmental Engineering Reference
In-Depth Information
water uptake coefficient that is decreasingly compatible with the hydrophobic
requirements.
The liquid water may penetrate between the bitumen film and aggregates,
resulting in the bitumen film becoming unstuck and plaster grains crumbling. Clay
swelling may also increase this phenomenon.
A slight superficial degradation by ultraviolet radiation through oxidation of the
bitumen alkanes may be considered acceptable [DUR 62].
Specific research on an extra bituminous paint was carried out. The purpose of
this extra paint layer is to restore the hydrophobic characteristics of weathered
plaster in the easiest way, using as few materials as possible. The bituminous paint
was prepared in the same way as the plaster, adding more water to produce a fluid
material. An application of this paint on weathered plaster showed a decrease in the
water uptake coefficient.
The preparation of the bituminous paint was not easy, however, and revealed
some stability problems as the bitumen flocculated to the surface. Micro-drops of
bitumen stayed on the paint and the building surfaces.
11.2.3.2.
Polychrome decoration
11.2.3.2.1. Painting techniques and material identification
The aim of the decorated surfaces study was to investigate stratigraphy and
painting technology, determine organic and inorganic components, and to identify
alteration patterns.
Cross-sections of the decorated surfaces indicated a succession of three different
layers applied on the earth relief. Material identification was accomplished through
EDX-analysis, X-ray diffraction and chromatography analysis. The three layers
were:
− A preparation layer of 2-3 mm thickness applied to the relief. The layer
presented angular grains of around 100 µm diameters, which showed that the
material was probably crushed. It was composed of a ferruginous earth with some
clay minerals (kaolinite) and fibers (see Figure 11.21). Hematite was responsible of
the orange color of the earth; fibers provided the material with a solid frame and
clays offered a sticky texture on which to engrave the drawings.
