Stone for Old
Techniques for Matching Historic Stone Finishes
by a student from City of Bath College,' the mallet and chisel are
of the type used for the work. The open texture of Stoke Ground
base bed can be seen (Jamie Vans)
Stone decay is a common
problem which lurks expensively in the background for many congregations
particularly if, as is often the case, the rainwater system has not been
properly maintained. In some areas of the country the local stone decays
very freely when saturated, in a sort of slow motion explosion, losing
all coherence and strength, but where it has not been saturated it often
survives so well that every mark of the chisel, axe or drag with which
it was dressed is still visible.
workmanship of stonemasons and builders is not always seen to its best
advantage where the common task of replacing severely weathered and damaged
stones on historic buildings is concerned. No matter how good the intentions
of the owners and the architect may be when carrying out repairs, it can
be difficult to achieve a style and standard of work which does not in
some way mar the appearance of the building. However skilfully it is carried
out, the insertion of new stone into a weathered wall is likely to have
a substantial impact on its appearance. Indeed, the visible differences
between old and new may actually increase with time especially if materials
have not been carefully chosen or if stone from a suitable source is not
available. Even the most essential improvements such as the provision
of an efficient rainwater system may perpetuate and accentuate any differences
by preventing the weather reaching the new stone, inhibiting or occasionally
increasing the accumulation of dirt, and preventing the growth of lichens.
Some disruption to the surrounding fabric is also likely, in the form
of damaged arrises, slight movement in the surrounding joints, and holes
made to insert the necessary temporary support for the remaining structure.
It is clearly necessary
to preserve as much of the original stonework of an old building as possible,
and if replacement is unavoidable, new work should normally be kept to
Sad to say, not every
builder or stonemason is capable of carrying out properly the work in
which he claims to be a specialist. It is extraordinary that so often
the owners of a building will entrust its care and repair to a complete
stranger chosen by competitive tender from a list of other strangers.
Taking up references and visiting at least one job of a comparable nature
offers no guarantee of quality workmanship but it must be the least that
anyone in that situation should do before adding a company name to the
The fact is that,
while it is often easy to see that a repair is unsuccessful, it is not
always so simple to specify a method which would have achieved a better
result. A number of difficulties stand in the way of anyone trying to
write a clear description of, for example, a particular style of chiselled
surface. Technical terms are often imprecise: when describing the texture
of chisel-marks for example, language is as infuriatingly uncertain as
when dealing with colours or flavours. Regional differences in craft teaching
and local practice, which are an essential part of the diversity of vernacular
building, only add to the difficulty of a specifier attempting to describe
what he wants the job to look like.
THE WAY FORWARD
essential first step before undertaking any stonework repairs is to establish
the cause of the problem and to determine whether work is really necessary.
The cause of any damage must always be dealt with as the first priority;
in some cases, simple improvements to rainwater goods or minor repairs
to a protective cornice or string course above an area of damaged stone
may make expensive structural repairs unnecessary.
on which and how much stone to replace inevitably have to be made as work
proceeds, largely based on the skill and judgement of the subcontractor.
The appointment of stonemasons who are able to interpret the requirements
of the building and the professional is therefore vital
SELECTING A CONTRACTOR
work on the Grand Stair repairs at Woodchester Mansion, near Stroud, Gloucestershire
was undertaken, members of Woodchester Mansion's fabric committee visited
the workshops and a current work site of ten contractors before inviting
a short list of six to tender for the contract. Only then could the committee
be confident that any of the chosen companies could be relied on to provide
workmanship of the right quality in all the relevant trades.
delegate at a recent COTAC conference described the 'two envelope'
system of tendering, according to which each contractor returns his bid
in two separate envelopes. The first to be opened contains the names of
the key personnel who will be involved in carrying out the work; the second,
which is opened only on condition that the first has given satisfaction,
contains the figures.
was also suggested at the conference that both clients and contractors
might benefit if it was made clear from the outset that the tender accepted
would be not the lowest bid but, for example, the bid closest to the average
figure. This would help to ensure that a sensible figure was arrived at,
rather than trying to do quality work on the cheap.
is common practice to build a trial section of walling or to work some
exemplar stones to be approved before they are inserted into the building,
but even this is far from infallible. Any panels of sample stones will
usually have been treated as of great importance and carried out with
particular care, often by one of the more experienced and skilled craftsmen
available; the main job, the really important bit, may not get the same
treatment. Impressive trials are therefore not a guarantee of success,
but they will help to eliminate some unsuitable contractors.
should particularly beware of the practice widespread in the stone trade
of employing unqualified personnel such as bricklayers for fixing stonework.
It is essential that the person who fixes the stone should be a qualified
mason; only then will he fully understand the importance of careful handling
and accurate bedding and be aware of any details which need adjustment.
on site (Figures 4 & 5) is by far the most effective way to achieve an
accurate reproduction of all forms of original masonry detail and should
be standard practice where a very high degree of replication is required.
If this is really not possible, a site visit for masons working on the
project is essential to allow them to see what is required of them, and
rubbings and photographs may be used to assist back at the workshop. The
extra expenses of working in this way may be compensated for by the improved
likelihood of achieving correct results first time.
SELECTING YOUR STONE
some areas such as the Cotswolds, where the stone can vary sharply in
character and quality from one small quarry to the next only a few hundred
yards away, the matching of stone on historic buildings has become something
of a nightmare. In the whole of the Gloucestershire Cotswolds, south of
the A40 from Burford to Gloucester, there is no longer any source of dimension
stone - that is, stone of sufficient size and quality to be sawn for worked
masonry - apart from one heroic company which quarries Tetbury stone.
Minchinhampton and Painswick stones, from which Gloucester Cathedral was
built, are long gone, as are Leckhampton, Dowdeswell, Stroud, Nailsworth
and many others. The stones of the North Cotswolds and from the Bath and
Corsham area usually allow the specifier to achieve a reasonable match
for colour and texture but the special character of many local materials
is lost, probably for ever. On the other hand, the more uniform output
of these larger quarries now in production certainly simplifies the choice.
Selection of stone is often dictated by availability above all.
the Grand Stair at Woodchester Mansion it was impossible to achieve a
close match from sources currently available in England or France. The
stone originally used has a characteristic banding of fine and coarser
shelly material which apparently does not occur outside the quarries of
the Stroud area. Rather than use another Cotswold stone with a strong
but different character, Monks Park was selected for the interior ashlar,
which is the finest grained of the Bath stones available. On the exterior,
where weathering was a factor, the top bed of Stoke Ground stone was used.
In both cases the effect is rather more bland than the stone of the original
building and the texture more regular. Availability of stone of sufficient
bed height was another factor in this selection.
ago, quarrymen and masons found that the more shelly and open textured
limestones were often more resistant to weathering than fine-grained stones
and scientific testing tends to confirm their view. It is, it appears,
not so much porosity (air space) in the stone which causes problems but
micro-porosity (very small spaces in which water can get trapped). For
copings and other weather surfaces, the original builders used a shelly,
often crystalline stone of the sort usually referred to locally as Minchinhampton
stone. The closest match for this might have been Clipsham but the Stoke
Ground base bed, which has a coarser texture than the top bed, will weather
in convincingly in a few years.
the past, when stone was worked by hand from an early stage, the finish
was often the end result of the production process itself. Because the
mason who made the original tool marks was trying to get rid of the excess
stone, he went at it with a will; his tool marks were often bold and deep
as a result. Today stone will very often be sawn to size and the finish
will be applied by the mason as a sort of distressing of the surface in
the belief that he has only to dent the 'perfect' sawn surface to achieve
the appearance required -indeed to do more would be considered 'wrong'
as his straight edge will tell him. Furthermore, the mason's tool tends
to leave only a superficial mark as it skids off the smooth sawn stone.
Working from an already flat surface also tends to lead to a uniform and
mechanical style of tool marks. In these circumstances it may be that
the masons have to be encouraged to relax and to worry less about straight
lines and strict accuracy; with practice and a more relaxed hand, a mason
will still achieve good results.
observation of the nature of the surface to be copied is essential if
the final result is to be a good match. Chisel and axe marks can usually
be distinguished by, for example, the shape of the mark made by the tool.
When the heavy Cotswold-style axe is used in the traditional way for stone
production, rather than simply dressing the face of a stone, it makes
broad, flat marks, unevenly distributed and often radiating slightly as
the mason has turned to reach along the stone rather than moving his feet.
Beds and joints are cut roughly square with the axe. The result (Figure
2) is a very lively surface which was then normally flush pointed and
limewashed to protect it from the weather.
To preserve the characteristic
surface textures of the different parts of the building, a mason must
look closely at the stones around the work area and to develop a method
of matching their character. Observation, experimentation and practice
are essential. It may well be necessary to experiment with different tools
and techniques, using different chisels, weight of hammer or mallet or
sometimes an axe.
The most common stone
finishes used on vernacular buildings constructed of limestone fall into
seven main categories (although these might or might not be understood
by another mason in the same way):
- Axed as part of
the process of stone production - marks usually broad, unevenly spaced
and varying considerably in direction (Figure 2)
- Axed over a sawn
surface (Figure 3), for cosmetic effect only - more regularly spaced
marks with a shallow scoop, often with flats between the marks
- Chiselled as part
of the process of production (Figure 7) - similar to an axed finish,
but usually with marks narrower and more regular
- Chiselled over
a sawn surface (Figure 7) - often the chisel is driven into the stone
rather than taking out a scoop
- Batted (Illustration
at start of article) - regular chisel marks at consistent angles and
in straight rows
- Batted margins
(around the edge of the stone only; used commonly in Portland but rarely
in the Cotswolds)
- Dragged (drags
are also known as combs) - often used for dressings with rubble walling
and for ashlar (Figure 8)
- Pitch-faced or
rock-faced, mostly on 19th century buildings (Figure
chisel marks are also occasionally seen though these would not normally
be considered to be correct (confusingly, claws are also sometimes known
This list is undoubtedly
far from exhaustive, but it may help to draw attention firstly to the
variety of finishes which have been commonly used, and secondly to some
of the techniques which may be employed to match the works.
Points for Specifiers
key recommendations may help to bridge the gap between the vision
of one man and the finished job of another:
- Ensure that
the proposed work is really necessary and not proposed for purely
- Check that
any defects which have led to stone being damaged are repaired
- Choose new
stone as close as possible to the original in geological type,
colour, texture, porosity and hardness; be aware of the way the
new stone weathers compared with the original materials
- Match mortar
materials and pointing techniques
- Copy the
size of beds and joint sizes; if these were not originally uniform,
ask for a similar variation
- If the original
stones were hand-dressed and were not accurately squared, insist
on some hand-working to similar tolerances
- Be specific
about the required surface on the new stone; tooled or chiselled
can be interpreted in many different ways; use rubbings, photographs
and drawings to illustrate the point
dressing of ashlar and rubble stone in situ should not be necessary
and is undesirable as it may cause damage to mortar and stone
- Working the
stone on site is the best way to replicate an existing style.
article is reproduced from The Conservation and Repair of Ecclesiastical Buildings, 1999
VANS is a stonemason and
sculptor with over 20 years experience in working and conserving stone,
who now works part-time as Director of Training for the Woodchester
Mansion Trust. The Trust provides a unique opportunity for trainee masons
to practise the important skills of work on historic fabric as well
as running a programme of short practical courses for architects and
other professionals. For
further details see:
PRODUCTS AND SERVICES
Communications Limited 2010