Comparison with the earlier initial test, constructed using conventional mortar is quite interesting. The test sample was 100 mm
in thickness. The flexural stiffness, prior to cracking, corrected to a
width of 320 mm was 60.1 109 mm2 compared with 196 and
33 109 for the 100 mm deep panels using Clashach and Stoke
Hall stone respectively. Both the depth and the spacing of joints
was the same for all beams. The initial test panel was constructed
with a variety of available stones. The Woodkirk and Cat Castle
stones share a similar petrographic history to Stoke Hall, being
geologically earlier coarse grained gritstones compared with the finer grained mudstone Clashach. The stiffness is clearly less than
the stiffness of the stone itself (assuming properties similar to
Stoke Hall. The interaction between bedding layers and brick or
stone is complex, with relatively little research. Hendry [13] reported on tests on the compressive strength of brick masonry using
differing bed joint materials including mortar, steel and rubber.
Thin steel increases the strength brick assembly by more than
40% of the strength of the brick itself whilst rubber joints resulted
in a 87% reduction in strength. More recently [14] tests on sandstone have shown that the stiffness of sandstone in axial compression is strongly affected by the nature of the bed-joint, with dry
joints exhibiting greater stiffness than mortar joints.