Data from: The benefit of a tough skin: bullet holes, weathering and the preservation of heritage

Projectile damage to building stone is a widespread phenomenon. Sites
damaged 100 years ago during the First World War still see daily use,
while in a more contemporary setting numerous reports show the damage to
buildings in Babylon, Mosul and Palmyra. While research has been carried
out on the long-term effects of conflict such as fire damage, little is
known about the protracted damage sustained through the impact of bullets,
shrapnel and other metal projectiles outside of the field of engineering
focused on ceramics and metals. To investigate alterations to mineral
structure caused by projectile damage, impacts were created in
medium-grained, well-compacted, mesoporous sandstone samples using 0.22
calibre lead bullets shot at a distance of 20 m. Half these samples were
treated with a surface consolidant (Wacker OH 100), to mimic natural
cementation of the rock surface. These samples were then tested for
changes to surface hardness and moisture movement during temperature
cycles of 15–65°C. Petrographic thin section analysis was carried out to
investigate the micro-scale deformation associated with high-speed impact.
The results surprisingly show that stress build-up behind pre-existing
cementation of the surface, as found in heritage sites that have been
exposed to moisture and temperature fluctuations for longer periods of
time, can be alleviated with a bullet impact. However, fracture networks
and alteration of the mineral matrices still form a weak point within the
structure, even at a relatively low impact calibre. This initial study
illustrates the need for geomorphologists, geologists, engineers and
heritage specialists to work collectively to gain further insights into
the long-term impact of higher calibre armed warfare on heritage
deterioration.