T W E N T Y F I R S T E D I T I O N
T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 4
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3.1
STRUCTURE & FABRIC :
ROOFING
wall sometimes need to be reconstructed, for
example when inappropriate repair materials
have been used.
In many of these instances the preferred
method of repair is to use air dried clay blocks
laid with a clay dabbin mix as a mortar.
In some cases clay tile or thinly bedded
sandstone can be used to tie new work to old.
As a modern alternative lightweight, twisted
stainless steel reinforcing rods (Helibar for
example) can be fixed into the original clay
wall and laid across the new clay blocks (top
right).
Small cracks which do not continue all
the way through the wall can be treated by
stitching across the crack using small adobe
blocks. A small trench, which is large enough
to take the block and a quantity of the clay
dabbin mix as mortar, is cut horizontally
across the crack. The trench is well wetted
before the clay block is pushed into the mortar
so that the entire cavity is filled by the block
and the mortar and the excess is squeezed
out of the front. Depending on the length of
the crack there should be a stitch about every
350mm, starting at the base and doing one
stitch at a time. The gaps between the stitches
can be opened up slightly, damped down and
filled with mortar and small pieces of adobe
block (bottom right).
Major cracks that carry all the way
through the wall will probably need to
be investigated by a surveyor or other
professional, as the cause of the cracking may
need to be addressed. Any remedial work
will need to be carried out by a competent
professional, particularly if propping is
necessary. Sometimes when the gaps are wide
the cracks have been built up in brick or stone,
often using cement mortar. If it is thought
prudent to remove the brickwork and replace
it with clay block, then this needs to be very
carefully controlled.
Surface hollows are very common in
clay dabbins and if they do not create large
overhangs then they could be left alone and
simply rendered. These surface depressions add
to the character of the building. Hollows that
are 100mm deep can be treated by cutting into
the clay wall, providing a flat base on which
to lay clay blocks bedded in a clay dabbin mix
used as mortar. As before, the cavity should be
Cumbria might see a revival in the clay dabbin
tradition with the construction of new homes
in the near future.
Recommended Reading
J Hurd and B Gourley (eds), Terra Britannica,
James & James, London, 2000
L Keefe, Earth Building: Methods and
Materials, Repair and Conservation, Taylor
& Francis, London, 2005
J McCann, Clay and Cob Buildings, Shire,
Princes Risborough, 2004
P Messenger, Caring for Clay Dabbins: A Guide
to Construction, Repair and Maintenance,
North of England Civic Trust, 2012
(available online at:
resources/hsi-guides)
R Nother, The Repair of Earth Walled
Buildings, IHBC Conservation Guidance
Note, 2000, (available online at:
org.uk/resources/advice/guidance/advice.
html)
GT Pearson, Conservation of Clay and Chalk
Buildings, Donhead, London, 1992
J Schofield and J Smallcombe, Cob Buildings: A
Practical Guide, Black Dog Press, Crediton,
2004
A Weismann and K Bryce, Building with Cob:
A Step-by-Step Guide, Green Books, Totnes,
2006
C Williams-Ellis et al, Building in Cob, Pisé
and Stabilised Earth, 1947, Donhead,
Shaftesbury, 1999
BSc(Hons) MA Dip TP
IHBC MRTPI is a historic building and
conservation consultant living in Cumbria.
He was formerly principal conservation
officer for Carlisle City Council.
thoroughly wetted before starting. On larger
areas it is often necessary to key the blocks
firmly to the original wall. Various armatures
have been used in the past. Oak pegs or clay
tiles can be fixed into the wall, although tiles
can be awkward to fix and can detach from the
slots that have been cut for them. Lightweight
Helibar rods can also be effective in this
situation.
Deeper hollows can be treated in the
same way but with greater caution as this
kind of repair is essentially underpinning and
there may be a need to support the wall while
someone is working on it underneath. If in any
doubt about the structural integrity of the wall,
specialist advice should be obtained.
Finally a word on rat runs. These are
continuous cavities that are sometimes found
inside a clay wall. They are fairly common in
buildings near or on farms and have probably
been excavated by rodents. Attempts may
have been made to seal or block them up
with anything that came to hand, including
broken glass and barbed wire. If the runs are
extensive then seek advice as to the stability
of the wall. If all or part of the cavity can be
cleaned out, bearing in mind the hazardous
material you might find, then it can be filled
with a grout of lime and coarse sand. Again
dampen as much of the cavity as possible
beforehand without saturating the clay wall.
If the holes are large, mix in coarser aggregate
and if necessary push it in with a rod. This
may not completely fill the run but it will have
reduced the amount of unsupported clay and
improved the wall’s stability. If the run is close
to the surface then it may be possible to expose
the cavity and treat it as a hollow (see above).
THE FUTURE
The Clay Dabbins Project made both
professionals and the public aware of this
important part of Cumbria’s built heritage,
one that has been diminishing rapidly over
the past century. Since the project began in
2009, the public’s appreciation of clay dabbins
has dramatically increased, and the skills
and knowledge of builders, contractors and
professionals have improved to the point
where the repair of existing clay buildings is no
longer a lottery. There is even the possibility,
with so much focus on sustainability, that
Finishing off the gables of the clay dabbin
Helibar ties laid along the courses of clay blocks
(Photo: Little and Davie Construction)
Stitching minor cracking (Photo: Little and Davie
Construction)
