Flint and the
Conservation of Flint Buildings
John Ashurst and Gerry Williams
is a fine example of knapped flint work, with shaped flints
forming a fish-scale pattern
donor of the knapped flint from Kent writes that an operative
capable of knapping is now difficult to find', reported John Watson
in British and Foreign Building Stones (Cambridge University Press)
100 years, two world wars and a building industry changed almost
beyond recognition since Watson completed his Sedgewick Museum
catalogue of stones, it is not surprising that flint craftsmen
are not the easiest of skilled tradesmen to find. Which is not
to say that flint has been forgotten, nor that it has fallen out
of use. On the contrary, in some parts of the country there is
a revival of sorts, with flint being cast as a facing to concrete
slabs, and flint veneers raised as decorative panels over blockwork
in conservation areas.
There is nothing wrong and much to be said
for new uses for traditional materials; but sadly, rather than
a 'new use', flint is now emerging from these production lines
in an awful parody of traditional flint masonry. Small faces of
flint peer out from heavy frames of grey or yellow mortar, scarred
with brush marks. When seen juxtaposed against the fabric of older
buildings the experience is particularly dismal. This work cannot
be more offensive to anyone than to the few surviving craftsmen,
especially of Norfolk, Suffolk and Sussex.
CHERT AND JASPER
example of polychromatic flintwork by Wyatt at West Dean is
shown, with the window surround picked out in black using
examples of bad repair work: (above) an ignorant reconstruction
with widely spaced flints set in a sea of hard cement mortar;
and (below) original flintwork repointed with a thick ribbon
of cement mortar in a parody of the snail creep detail. In
the lower example a sea urchin can be seen forming the core
of one of the flints.
Flint is one
of three closely related forms of compact crystalline silica which
have been used in building, and the most common. It is found in
the top part of the middle and throughout the upper division of
the Chalk geological formation. It is closely related to quartz,
chalcedony, chert and jasper. The hardness of these materials
is well known: they are resistant to scratching with a knife blade. In
the context of building, flint, chert and jasper are the important
rocks, with flint the most common and humble, and jasper, which
St John tells us will be the stone of the new Jerusalem, the most
Flint occurs as nodules or in bands within the Chalk,
and can be seen primarily in the counties of Dorset, Wiltshire,
Hampshire, Sussex, Kent, Surrey, Berkshire, Suffolk and Norfolk.
Its origin is generally accepted as being the siliceous sponges
once inhabiting the waters of Cretaceous seas. Flints which have
been washed out of the chalk cliffs can also be found as rounded
cobbles and pebbles and have been used extensively for building
chert are concretions, that is to say natural growths of mineral
matter which form around a centre or core. Sometimes the core
may be seen to be the sea urchin. The silica solutions from which
flint was precipitated either displaced an equal volume of chalk,
or flooded pre-existing cavities perhaps formed by marine borers.
The colours of flint are black or dark blue-grey, and they are
usually nodular in form, commonly coated in a white cortex of
calcium carbonate, but tabular forms also occur.
The nodules break
with a conchoidal (shell-like) fracture, forming sharp edges which
have always been valued for their cutting potential. Elaborate
and sometimes sophisticated tools such as axes, adzes, spear points
and arrowheads were made from flint by early man by hammering
and flaking 'green' or freshly mined flint, anticipating the later
production of knapped flints and gun flints, which were produced
with similar techniques.
Chert is not
always easy to distinguish from flint. Also known as hornstone,
it is generally the name used for silica beds, nodules and layers
which occur in limestones other than the Chalk. The fracture is
more 'hackly' than conchoidal. The use of chert in building tends
to be very local and can be seen for instance in Chard, Somerset
(sourced from the Upper Greensand) and Colyton, Devon, or in Richmond,
West Yorkshire (sourced from the Carboniferous Limestone).
an opaque form of chalcedony, is usually red, but can be yellow,
brown or green. Gwynedd, North Wales, was once a well known source.
In modern times it has occasionally been used for decorative purposes,
a good example of which can be seen in stall risers in Piccadilly,
London at its junction with St James Street.
extensive exploitation of flint for building is Roman, predominantly
but not exclusively in the core work of composite walls. Where
flints were abundant, as along the south and east coasts, they
were used in prodigious quantities, laced with levelling and bonding
courses of square bricks.
Norman churches also made extensive use of coarse but unsplit
flint, a practice which continued in the flint regions throughout
the Middle Ages. More sophisticated and architectural use of flints
dates from around the beginning of the 14th century, when knapping
and squaring of flints produced flat surfaces which could be framed
in limestone, the practice known as 'flushwork'. Flushwork became
highly fashionable and at times adventurous in the late 15th century
and it continued to be popular for about 100 years. From the time
of the first Elizabeth, flint was increasingly used in combination
with other masonry materials such as limestone, sandstone or brick,
in bands or chequer-work. Except for utility buildings it is generally
the case that brick took the place of flint in its traditional
regions during the 17th and 18th centuries.
A revival in the use
of flint had to wait until an interest in the Romantic developed
in the late 18th century. The flint garden grotto of the great
houses is a symbol of the taste of the time. Flint cobbles were
used extensively along the 'flint shores', often tarred or colour
washed and in the Victorian period a whole range of flint buildings,
coupled once again with limestone or brick, reappeared. This new
fashion in flint extended from cottages and church restorations
to fortifications and even great country houses.
1 Joints in Flint Masonry - mortar profiles
2 Joints in Flint Masonry - use of gallets
AND CONSERVATION OF FLINT BUILDINGS
legacy of flint construction presents something of a challenge
to modern owners and conservators. Too often, repairs seem to
be carried out by the uninitiated (and are sometimes specified
by them too). The tough, intractable, siliceous nature of flint
is the source of its great durability; but this durability is
confined to individual units and not necessarily to flint masonry.
To a non-expert, flint is not only difficult to split and shape,
it is also difficult to raise as a vertical wall even in its rough,
nodular, field-flint form. This is why so much mortar is used
in which the irregular flints are set like currants in a cake.
True, more mortar is needed than for regular units such as brick,
but somewhere in the wall the flints need to touch each other
and lock together as much as possible within the mortar matrix.
importance of mortar is paramount. The Saxon Shore forts such
as Pevensey or Portchester, built in the late third century by
the Romans, survive in an aggressive environment because of the
quality of their mortar. In these early years the mortars were
lime, ash and (commonly) brick aggregate and brick or tile pozzolan.
Where no reactive volcanic ash was available (true pozzolana)
ceramic pozzolans were used extensively throughout the Roman world
to impart a hydraulic set to their mortar. Tile or brick fired
at low temperatures and crushed to a fine particle size reacted
with some of the lime to form calcium aluminates and silicates,
is almost always found during analysis of Roman mortars.
were ideal for masonry use; their permeability (their ability
to allow water to evaporate through their pore structures), adhesion
and flexural strength (which enables masonry to accommodate minor
movements without cracking), ensured good, long-term performance.
Later builders used lime mortars without ceramic powder but still
containing significant quantities of kiln residues which could
also impart a weak hydraulic set; or they used natural hydraulic
limes such as those from Lewes in Sussex or Dorking in Surrey
for their flint work. Analysis has shown that additions such as
tallow or beeswax were also sometimes included, added when the
lime was being slaked.
The use of
similar mortars to the traditional types in repair and conservation
is absolutely essential to good practice. Yet time and time again,
partly misled by the strength characteristics of flint units and
partly because the building industry is still locked into the
use of cement, flint is raised in cement or masonry cement mortar.
Not only is this, visually, a lifeless material, it develops shrinkage
cracks around flints and forms continuous cracks through the mortar
to accommodate movement inevitably caused by thermal and moisture
changes. In addition to these problems, cement rich mortar inhibits
the free evaporation of moisture which enters through cracks,
and contributes to the overall dampness of the wall. In occupied
buildings this is uncomfortable and unhealthy; in freestanding
walls the masonry often falls victim to frost.
The most common
occurrences of failure in flint walls are detachments of the flint
faces, with or without the cracking associated with inappropriate
mortars. Where detachment and major cracking occurs, the area
affected must be taken down and rebuilt. All situations require
that the character of the work is recorded and properly observed.
Not all flint work, even of modest character, is as random as
it might seem; there is usually coursing and the flints may be
set in opposing diagonal lines as in the Roman 'opus spicatum'
('herring bone'). Without careful observation of the flint masonry
as found, rebuilding and repair can change its character quite
subtly and adversely. Sometimes there is fugitive evidence of
jointing patterns and profiles (Figure 1), or the joints may be
set with small shards of broken flint called gallets (Figure 2). All such detail needs to be put back.
bonding of the flint face to its backing is a very important detail,
even if there seem to be no bulging or loose flints present.
Long tailed flints well anchored in hydraulic lime mortar provide
the best method of bonding, but stainless steel wire ties or anchors
can also be used. The backing or core may also need some consolidation
as it varies from well built, well compacted brick and flint ('bungaroosh')
to loose, rubbishy fill with little structural capacity ('ragtush').
Sometimes hand grouting of local voids with a proprietary grout
or hydraulic lime may be necessary to supplement tamping and pointing.
A suitable proprietary grout might contain a suspension of pulverised
fly ash (a form of coal ash), hydraulic lime and bentonite.
mortar is cut out in much the same way from flint masonry as from
other traditional masonry, although the depth of cutting out may
need to be increased. Sharp tungsten tipped chisels should be
used. If an aggressive mortar has been placed to some depth, which
is unusual, it may help to carry out some 'stitch drilling' with
a masonry drill first. The flints and backing need to be well
wetted and if new flints are being used they need to be soaked
in clean water before being placed. Mortar must be placed with
great care, ensuring thorough compaction and filling of all irregular
voids, and the final pointing needs to be cured slowly. During
the curing process any shrinkage needs to be closed up with pointing
keys as it occurs. Successful work cannot be carried out unless
a suitable range of tamping tools and pointing irons is available.
Typical mortars are as follows:
- sheltered exposure lime putty 1 : well graded sharp sand
1.5 : porous limestone 1.5 : brick pozzolan 1
- moderate exposure natural hydraulic lime (NHL2) 1 : well
graded sharp sand 1.5 : porous limestone 1
- severe exposure natural hydraulic lime (NHL3.5) 1 : well
graded sharp sand 2.
THE NEEDS, MEETING THE CHALLENGE
examples which illustrate the versatility of flint: (above)
the irregular shape of field flints which have been used as
found; and (below) the neat, regular appearance of flush work,
in which the flints are first split and knapped.
This is the
subtitle for Traditional Building Craft Skills, a recently published
report commissioned by English Heritage, the National Heritage
Training Group, and CITB. The report identified on a region by
region basis the percentage of contractors and sole traders having
at least one employee with a specific craft skill, one of which
was 'flint knapper'. Of the principal flint regions, East of England
and the South East recorded five per cent (the highest) and three
percent respectively for their flint knappers. The East Midlands
recorded two per cent, the South West region, North West and West
Midlands all registered one per cent. London had no source. Only
the South East recorded a requirement for a significant regional
inflow. Assuming flint knapping implies another ability, that
of raising knapped and other flint work, and in spite of some
nil returns on requirement forecasts, it is clear from the condition
of our flint heritage that there is a critical shortage of skilled
are centres where flint knapping and building are still carried
out and where there is training potential. One of these is based
at West Dean College in West Sussex where flint forms the subject
of one of the English Heritage validated building conservation
masterclasses. Great importance is placed on the quality of repair
and the training expertise available in-house forms the basis
of the flint masterclass.
House is one of the best examples of 19th century flint work in
the country, the main facade being the work of James Wyatt, commissioned
by Sir James Peachey in 1804 and completed by Wyatt's son Benjamin.
Unlike its neighbour, Goodwood House, the flint for West Dean
was brought from Norfolk for its supposedly superior quality.
The full potential of flint and flint working skills is seen in
the detailing of the house. Quoins are formed in square black
flints; window reveals are knapped flint cavettos; the porte cochere
is of limestone and flint flush work. Neat galleting of various
kinds is obvious in all the work. Around the estate flint is used
extensively but in far more modest ways.
As with all
traditional building materials and building techniques, pressure
for change in maintaining sources of materials and for development
of continuity and training begins with an awareness of the significance
of our flint heritage and the threats to its survival.
article is reproduced from The Building Conservation Directory, 2005
The late PROFESSOR
JOHN ASHURST DArch RIBA EASA (Hon) was a former Principal Architect
with English Heritage. At the time of writing this article, he was a consultant at Ingram Consultancy
Ltd and a consultant to West Dean College on the building
WILLIAMS is a flint mason at West Dean College and teaches
the flint masterclass.
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