Civil Engineering Reference
In-Depth Information
Chapter 2.3
Stone rubble and ashlar
This chapter deals with natural stone
as quarried, but used in thicknesses
of more than 100 mm as a
loadbearing element. When in
thinner sections as non-loadbearing
and carried on a separate frame it is
dealt with in Chapter 3.1. Cast or
reconstructed stone is a form of
concrete, albeit made with carefully
selected aggregates to match natural
stones, and in most respects can be
treated as a type of concrete. See
Chapters 2.4 and 2.5.
Where stone is quarried locally,
and there are several centuries of
tradition in its use, there is no doubt
that natural stone can form a durable
and attractive external wall,
weathering well over many years
(Figure 2.36). However, there are
certain basic points to bear in mind
when repairing or maintaining
stonework. This topic, however,
cannot possibly deal with detailed
conservation issues, and reference
should be made to
The weathering of
natural building stones
(113)
.
During the period 1991-94 it was
reported that about 1 in 12 of new
dwellings had external walls which
used natural or reconstructed stone in
the external leaf.
coursed. Uncoursed stone as cut from
the quarry used often to be laid
selectively, either, depending on its
nature, without any further dressing
or, at best, a blow or two from the
mason to get a closer fit. This is
commonly termed common or
random rubble. The quoins are often
partly dressed. Where the wall is of a
thickness greater than that of twice
the average width of the stones,
bonding stones, sometimes called
through stones, are laid for the full
width of the wall to prevent the
wythes parting. In many areas of the
country, mortar was simply clay or
earth gathered from the site, though
better class work will be found laid in
lime mortars. This kind of wall has
strong similarities with dry stone
walling, except that to enhance
weathertightness it was normally
rendered or harled. It will not be
found built much above one and a
half storeys in height when built with
clay mortars.
Where the rubble wall was
intended to be left unfaced, that is to
say with the stone exposed, the
degree of dressing of the stones was
often increased, and the stones laid to
courses. Terms used, which reflect
the degree of working and the sizes of
stones incorporated, include
uncoursed random rubble, irregular
course or snecked random rubble,
and coursed rubble (Figure 2.37 on
page 104). Walls built to courses are
much more consistent and stronger
than those which are not, and are
more amenable to calculations for
strength and stability.
Characteristic details
Basic structure
Rubble
Stone rubble walls can be found in
many different forms, varying mainly
on the amount of dressing given to
the stones and whether or not they are
Figure 2.36
This Cotswold village has a remarkable consistency imparted by the limestone from which
the majority of its buildings are constructed
