『Abstract
This research identifies the changes which takes place in roofing
slate due to natural exposure and tries to replicate these changes
experimentally. Traditional methods of testing, used by the British
and other national standards, concentrate on the properties of
unweathered samples and give no information on the relative durability
of the different slates. Instead of concentrating on the initial
properties, this research focuses on changes in the properties
in order to assess durability. The effects of natural weathering
were assessed by comparing old, used slates with new slates from
the same or a similar source. The new slates were then weathered
experimentally by repeated cycles of wetting and drying, and the
increase in water absorbency compared with that observed in naturally
weathering. Mineralogical differences due to both natural and
experimental weathering were also measured using X-ray diffraction
analysis. It was found that the effects of experimental weathering,
using repeated cycles of wetting and drying, are similar to those
observed in natural weathering. These include increased water
absorbency and loss of crystallinity of the principal minerals.
The greatest changes are found in those slates which are the most
vulnerable to weathering, making it possible to identify poor
quality slates.
Keywords: Roofing slate; Durability; Provenance』
Introduction
Context
Experimental weathering procedures
The wetting and drying test
Methodology of the current study
Test pieces
Experimental observations
Changes in water absorbency due to natural weathering
Identification of slates
The age of the slate
Welsh grey slate
Welsh purple slate
Cumbrian green slate
Ballachulish slate
Easdale slate (Toberonochy)
Spanish slate
Mineralogical changes in naturally weathered slates
Quartz
White mica
Chlorite
Changes due to experimental weathering of slates
Water absorbency
Mineralogical changes
Comparing the effects of natural and experimental weathering
Conclusions
Acknowledgments
References