CHAPTER XIV

BUILDING STONES AND ROAD METALS

I. BuiLping StoNEg!

BuiLpiNnG stone may appear so durable that it might be
expected to last for ever; yet some stone buildings decay
with deplorable rapidity. The outer stone of most of Westminster
 Abbey is said to have been replaced five times.
The British House of Parliament, built in 1840-50 of stone
recommended by a Royal Commission whose report (1830)
was for long the standard text-book on British building stones,
has crumbled so fast that its ornament has been partly
replaced by cast-iron, and the Members of Parliament were
warned in 1925 not to stand within 3 feet of the walls to avoid
falling fragments. The quickness with which stones decay
may be realized in any old churchyard, for it is rare to find
an intelligible inscription on a tombstone more than 200
years old, unless it has been recut. Poor stone is less durable
than good timber. Most of the buildings that have lasted
six or seven centuries are churches, which were built by
religious fraternities who would have regarded the use of
inferior material as sacrilege.
Cavuszs oF DEcay—The decay of building stone is primarily
due to the entrance of water, which weakens or dissolves the
cement and introduces material that, on solidification, disintegrates
 the stone. The early builders therefore designed
projecting dripstones, string-courses, and gargoyles to throw
the rainwater off the building. The injurious effect of
moisture is often shown by the decay of the under surface
of projecting stone, and in the lower part of a wall which

lds ; he testing
J. A. Howe, The Geology of Building Stones, 1910; for t :
of La 7. Hirschwald, il bautochnischen Gesteinsprifing,
Berlin, 1912,