“Stones ~ To Be or To
Appear...”
Maisons & Décors
Méditerranée n°119 - Déc. 1993 / Janv.
1994
Christophe CADU-NARQUET
Heritage
:
Before any work is undertaken,
a façade must be judged
with regard to the style
of the period when it was built.
The architectural details of the façade
enable us to understand how right the alterations to be made will be and
avoid big mistakes such as the syndrome of " exposed stone ". In
as far as the techniques to be used for cleaning and treatment of stone diseases
is concerned, the professional is the only person to be trusted..
The main difficulty lies in judging
a façade with regard to the style of its period and region.
If this is not done, then there will ensue amalgame, collusion, mix-up,
that is to say the worst things you could imagine, and very often
what is done cannot be undone. We can see pseudo-renovations which
are more like a pastiche or a copy or a fantasy... inappropriate
indentation of roofs, wrong-sized windows, wrong tiles... everything
wrong including the choice of material....
"A building must be understood
in its evolution which must be treated with respect " (*04).
|
Photo P.M.
A
troglodyte dwelling in the Beaumettes,
whose dry stone wall
must be preserved as it is. Squared stones, cut stone framing
the windows, corner chaining.
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Concerning the corner
chain-effect building, in uncovered, cut stone or coated
in the South of France, the example of Toulon can be of help
to us.
In the mid 18th Century, the façade was composed of
alternate coated stone and parts in stone cut to correspond
to the principal lines or the framework of the composition
: chain-effect, bands to decorate the different floors or
sills and front doors.
Under the influence of the neo-classical current around 1780,
there was a fundamental change in façades. They were
no longer designed separately but as a group and the architectural
elements were accentuated. The corner chain-effect building
became a large enough support
to be visible and keep its proportions with regard to the
length of the building.So the round shape disappeared as
it was too small and the console cornice became huge….
At the beginning of the 19th Century, the coating simulated
the bed of stone,by use of an iron grooving (*05). Thus there
is not just one image of a town, but, on the contrary, different
images which follow on and are not necessarily like one another….
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Denuded, put to death !
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When observing the refacing
of façades, you can note that on the whole stone is
more and more enhanced... So much the better ! we would be
tempted to say. Alas, no ! The big come-back of the fashion
for " exposed stone " by owners wanting a rustic
style is often irremediably harmful. The façades in
streets, squares have gradually been spoilt and have taken
over from ancient and traditional architecture. The defenders
of this so-called free restoration (*04) expressing the current
tendancy to rehabilitate ancient houses with neo-regional
elements which are quite simply caricatures.
It is time we reacted vigorously. The irreversible spoiling
of architectural elements should make us think ; do we want
to continue seeing our village or urban habitat disappear
just to satisfy our irrepressible modern needs, our way of
living, our absolute search for the sun...? Should we let
the syndrome or " monomania " of " exposed
stonework " (*04) invade all the villages in France
? Of course not ! Information and knowledge are the best
way of making people aware of the qualities of each individual
region.
|
(Photo B.E.E.)
Wall
whose facing, which was meant to be protected by a coat
(judging by the thickness of the window frames) has been
sanded and jointed.
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Stones of the fields and stones of the towns…
|
(Photo M. Maurette)
Farm
support wall or " restanque " made of dry stone with
no joints, erected by farmers with stones picked up in the fields.
Bonnieux.
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Above all, it is necessary
to make a distinction between two sorts of stone. On the
one hand " dry stones ",
resulting from the stoning of fields by women and children
with which most rural houses and farm buildings were built
with structural elements such as chain-effect, and window
and door frames being made of dressed stone.
When buildings are close to quarries
or if river transport is easy, whole façades , to
satisfy owners very much concerned by aesthetics, are made
of dressed stone (Arles,
vignon, Toulon, Marseilles)
Rural habitat is mainly made
of stones from fields meant to be covered, whereas more
urban architecture
displays and
develops all the different registers of dressed stone on
façades, showing it and ostensibly exhibiting it like
a town stone.
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Stone of the fields
|
Raw material, these stones
were used to build farm buildings, walls, restanques or " bancaous " little
shelters or other farming buildings such as bories, sheds
or wells. For the homes, they used stone that was hardly
squared so as not to weaken them. Crumbly, reacts badly to
extreme cold, permeable, easily crushable, it is a soft stone.
It is both the thickness of the building and quality of the
binder (fat limestone) that enabled (and still enable) these
insufficiencies to be compensated. In these conditions, moellons
were always used to be covered, protected and coated. .
|
(Photo
B.E.E.)
Wall of dressed stone and lintel in ogival arch from 15th Century
in the old town of Dragignan.
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Free stone
|
(Photo
B.E.E.)
On
the façade of Mougins church, bonding
of calcareous stones with sharp joints.
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Used over the centuries,
it comes mainly from a layer of limestone rock (*06)
Stone (its matter, grain and colour ) has always been highly
valued, the symbols of wealth and power being linked to its
cost. In order to remain exposed, the stone must be perfectly
prepared. It was carefully chosen (slight porosity, for example,
which guaranteed its long life,) its faultless implementation,
the finest possible joints to prevent water penetration into
the heart of the structure (causing fast degradation through
freezing) (*07)
Traditionally, free stone which was considered as the real
skin of a building, was dressed in many different ways (*08).
Indeed, the bonding, arranging and assortment of stones is
the aesthetic, even symbolic, function of a façade.
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Main quarries
| Stones
of the South of France : the main " molasse " stones in the Bouches-du-Rhône
are those of La Couronne**, les Baux (or Sarragan, chalky calcareous
with tight grains) Fontvieille (soft white stone with dominant
ocre colour and a medium-sized grain which is sometimes shelled),
St-Rémy**, Barbentane**, Bibemus** and Rognes (similar
to the stone of the Pont du Gard and Castilllon by its colour
and many medium-sized shells).
In the Vaucluse, the " lubéron
stones " :
Buoux (stone from the Roche d'Espeil which is greyish-white,
shelly, calcareous), Lacoste (white calcareous with a relatively
fine grain), Ménerbes (chalky, white calcareous, homogeneous
with a rather fine grain), Oppède (or pierre
d'Estaillades,
chalky white appearance, no trace of fossils, with a relatively
fine grain and no shine) and the stone of Grillon-le-Brave
(calcareous sandstone, non-freeze, with a medium-sized grain,
slightly shelly.
In the Gard, the stone of Vers-Pont du Gard, Castillon (straw-
yellow calcareous shelly, from a lagoon deposit after sea
withdrawal) and Tavel (very hard, siliceous limestone with
a very fine grain reacting well to shine, over cream and
blue beds, sometimes with alternate pink veins.) ;
In the Alpes de Haute Provence, stone from Mane** (used
to build Forqualquier cathedral) or Banon (hard limestone
with a very fine, bluey-grey or cream-coloured grain, reacting
well to shine).
In the Drôme, the stone of St-Restitut** and St-Paul-les-Trois-Châteaux**.
Provence Stone, or cold stone is mainly
located in Cassis (takes on a good shine) and in Mont Caume
(hard, reef calcareous,
compact and homogeneous, many fossils). These limestones
have been used for 2000 years for famous buildings such as
the Maison Carrée in Nîmes or Notre-Dame de
la Garde in Marseille (stone from Barutel-Gard) (*10).
** Quarries no longer in use
|
(Photo M. Maurette)
Spectacular orbicular stone of Cassis, calcareous marble worked
on here with a polished finish.
(Photo B.E.E.)
Toulon PRI., the composition of a wall. Dado in hard or cold
limestone from Pont Caume and wall in soft limestone (more yellowy
colour)
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Instruments, shape, lexical
| 
(Photo
M. Maurette)
Some tools, including a " boucharde " on
a stone with a raised chiselled finish and the
inside which is boucharded.
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The blocks
supplied to builders were cut in standardised sizes long
before the 19th Century
; they are called ; Queron (65x65x40) &endash ; Querade
(100x50X40) &endash ; Transpanière (100x40x40) &endash
; Bugé (64x50x30) &endash ; Carreau (70x70x45) &endash
; Cinquante carrré (50x50x45).
Pick, stamp, axe, big scissors, mass, mallet,
small two-headed axe, barley grain hammer, rustic, boucharde
(hammer with
one side with pointed teeth), scissors, serrated scissors,
gouge, slider, rail, these are tools used by the cutter or
jobber.
After being rough-hewed, thinned, erected, the stone
can then be hammered, rusticated, carved, slid along, or
boucharded
(fashioned with the hammer with the pointed teeth).
Depending on where the stones are meant to
be placed in the piece, they take on precise functions. Hardness
is one
of the most important criteria
And is classified in a standardised
way :
soft /sem-firm / firm / hard / cold (NF B 10.301) (*09)
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Lithochromiums** or natural colours
|
From the
Middle Ages to the 20th Century, the " image " of
architecture was dependent on the importance attributed
to the perception
of the materials. The value of stone was therefore recognised
as being ornamental and chromatic. According to the geographical
(quarry) and historical (period and style) context, the cut
of the stone is a reflexion of a symbolism with its effects
in texture and matter.
The ornamental use of stone was adapted
to local quarrying ; thus it is that the alternate facing
of black stone and
white marble (paramento litotomico bianco i nero) on the
façades in Lombardy, Pisa or Liguria in the 10th to
the 18th Centuries, whether they be for religious or civil
purposes is a remarkable example of that, as is the use of
dark-green Serpentine for the door frames in Cogolin (Var).
The polychromes of the walls of Romanesque churches , almost
mosaics, in Murano and aregno in Corsica, show both the variety
of balanine rocks and an elaborate sense of heraldry.
|
(Photo B.E.E.)
W hitewashed countertype
of stone shades. Hade chart
of the city of Toulon PRI
(Perimeter of Property Restoration)
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The
red-deep purple or grey-green shales of the Roya (Alpes Maritimes)
are often used as supports or frames for windows and doors.
As for the slate called Lavagna, from the name of the place
of extraction, it protects all the dados and decorates Ligurian
and Corsican portals.
Mainly used in the South of France,
limestones have more or less warm or coloured shades ranging
from grey-white through
light beige-pinks, cream, putty, light reddish yellows, pinky
coppers, blackish-brown, greyish-brown to grey-yellow-pinks.
Greyish shades and other more or less light greyish-blues
are attributed to cold stones …(*11)
These natural tones can be altered by a whitewashed patina,
but also change with the natural patina brought on by the
passing of time.
(** Lithochromium from the Greek lithos :
stone, and kronos : colour)
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Post
- colouring
In all times and for different
reasons stone has been covered by a coat of distemper. Whether
it be to hide the colour difference in the facing and uniformise
the wall, or to get it another colour and decorate specific parts
(polychromy in Roman times), in each case the role of distemper
as a protection has been recognised (and is now advised again).These
fine layers of deliberate colouring have not reached us , or only
very rarely so, because of degradation or destruction. So we meet
the problem of the relation between structure and decor. " Is
decoration an integral part of a building or is it just a more
or less rich covering put on once the shapes have been fixed ? " (*12)
The recent discovery of polychromium on Amiens cathedral has refuelled
the debate...
Very often the building which has been repaired does not correspond
to the original aesthetic objectives and in that case we can consider
applying a patina. A water patina such as aqua fortis (very diluted
coloured limestone milk) can be applied on the parts which have
been restored during the setting phase or, after three weeks a
silicate patina (95% potassium silicate) tinted with very highly
diluted mineral pigments (*06)
“Stone colour”
If the colouring of the surface of
stones has always existed, the ludicrous and destructive idea of " stone
colour " only came to light in the 19th Century. It is mentioned
in Roret's manuel for oil paints in 1884 as follows : 100 parts in
weight of white zinc for 6 of yellow ochre. In the 20th Century,
in the fifties and sixties, at about the same time as " egg
shell " this shade reappeared. Although there are many tones
to define calcareous stone, unfortunately this unique and final reference
was considered to be a symbol of good taste.
Weathering
|
(Photo
M. Maurette)
Weathering of calcareous stone. Flaking
of the layer on a wall not coated, sandy disintegration,
pluverulence and alveolisation seen through the presence
of little holes.
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Limestone is
more or less hard with over 75% of calcium carbonate in its
composition (*09). With a wide range of differing hardness
and texture,
These rocks can only be understood if we speak of their two
innermost elements which are calcin and sulphin (*13)
Calcin : Surface crystalisation (harder, more dense and
less porous than the little subjacent one, calcin), essentially
made up of calcium carbonate, ensuring a natural protection
for the stone while giving it a certain patina, a " cover ".
Sulphin : These blackish lumps, situated
in the porous substrata, contain a large amount of calcium
sulphate and
fine particles such as dust, tar, ash, spores, soot and
other matter contained in the atmosphere.
Unlike calcin,
they bring no protection and facilitate the development
of deep weathering : they can be taken
for the natural patina built up over the years.
Like all
other building materials, stone grows old and weathers
more or less quickly. Water has a preponderant
action on premature ageing and it is brought into the building
in liquid or gas form through running down the walls, transfers,
capillary rising or pumping phenomena. Combined with atmospheric
pollution (industrial, urban, agricultural) or a sea environment,
water becomes even more destructive.
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Disease
The changes in appearance, following
on natural ageing, bring about other surface weathering problems
called " stone diseases " and we list hereafter the ones
we know best. (*06 -*13) :
-
Sandy disintegration, superficial elimination of the
stone in a pulverising form, leaving the surface quite flat.
-
Alveolisation, grooves or cavities caused by running
water which disintegrates the stone
-
desquamation of the more or less hard superficial
layer of the stone is formed by deposits of dirt and chemicals which
end up
falling
off and tearing away the surface
-
Dissolution of the surface by acid rains or ill-adapted
cleaning
-
Biological attacks by expansive salts (created by
the nitrates or sulphates in the air or ground water) which settle
on the
stone and
cause it to break up.
-
Freezing causes breaking up,
chipping at corners or destruction by slabs on certain porous
stones (so freezable) after
repeated
bad
weather conditions.
Analysis
& Diagnosis
This first phase is indispensible
to understand the problems met. An examination must be carried
out by skilled professionals (project manager, company or approved
craftsman). The examiner must, as precisely as possible, identify
the original stones, their nature, their facing method and the
type of disorder (physical, chemical or biological). Only when
this has been undertaken, can technical solutions specific to
each pathology be proposed and then carried out.
Consolidation
|
In cases when stone has
kept its initial shape but lost a lot of binding and whose
surface resistance is too weak for it to receive repair
treatament, or even cleaning, then a mineralisation must
be undertaken in order to restore the initial mechanical
resistance of the stone ; the products normally used for
this are ethyl silicates or, more recent and better adapted,
silicate acid esters..
|
(Photo
B.E.E.)
Repairs to a 18th Century wall
of recuperated dressed stone with boucharding.
(Toulon PRI)
|
Cleaning techniques
There are four ways of cleaning stone : mechanically,
by sanding, with water and chemically. Each one is adapted to a different
pathology and has advantages and also its drawbacks. The resumé as
follows is meant to show the large range of possible treatments :
|
(Photo
B.E.E.)
On
the left, dirt-clogged stone façade. On
the left, after scrubbing treatment and protection
with silicate, the façade is beautifully
clean again. Toulon.
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Mechanical
treatment ; reserved for use by professionals of stone who
can perceive the original hardness of it and
thus only eliminate the damaged parts. Generally the tools
used are : a brass brush, rail (plane for stone), " ripe " (
a sort of file).
Sanding treatment (to be done by
specialists) : dry with siliceous sand, hydropneumatic
water/sand, scrubbing with glass microfines.
|
Water
treatments : long duration streaming, spraying, hot or cold
water under pressure, steam under pressure. These treatments
are practically all reserved for steles or statues. If these
techniques are used on house walls, then delicate conservation
measures must be taken.
Chemical treatments : neutral PH,
acid PH, alkalin PH products. These treatments may
only be undertaken after approval by the manufacturer
of the products to be used.
The use of a product with an inappropriate PH can lead
to irreparable damage being done. It is therefore absolutely
necessary, following diagnosis, to determine which
of the treatments (on its own or combined with others)
will be best adapted. |
Repairs
Repairs on
stone often take place when it is exposed, that is to say,
after the façade has
been cleaned. The choice of the type of repair depends on different
criteria taken into account : type and location of the repair.
Indeed, the repair will be different depending on whether it
is on a wall, floor, stairs, on moulding or a cornice, on a sculpted
part or a statue. (*06)
At all times, each Compagnon has always undertaken repairs to
stone using products formulated on the worksite based on stone
powder, slimy lime, hydraulic binder, natural earth and adding
agents. If these repair techniques are still widely used, they
are not always well-adapted. There exist several repair products
:
Glued
facings : if it is not possible to substitute, then stone
facing with thin coat of glue can be used
Reactive systems : either bi-components to be mixed very carefully
and for a very short time (5 to 15 minutes), or powder ready
to be mixed with water and to be used in 10 to 45 minutes.
Hydraulic type systems based on air lime, hydraulic binder
with many different mechanical and granulometric resistances.
There exist certain mortars to be used for redoing the
surface, filling in, reloading, moulding or finishing.
|
(Photo
M. Maurette)
Substitution of damaged elements
by stone
from a local quarry and cut
in an identical way following
the ancient architecural design. Uzès
|
Their
use, close to traditional mortars, must be in compliance
with the instructions for use.
Of course, it is necessary to follow a certain strict methodology for repairing
dressed stone, and, in conclusion, we must stress how vast the subject is and
how dependent on the nature and state of the stone. (*06) . |
Christophe
CADU-NARQUET
(Colourist at Patrimoine &endash ; Has managed the B.E.E.
agency in Nice for over ten years This activity has enabled him
to study history, architecture, colours, materials and techniques
and to define the rules for around fifty cities or villages, including
the ancient centres of Arles, Gap, Toulon, Dragignan, Nice, Grasse,
Ajaccio...and the regions of Balagne and the Ligurian riviera.)
In “Maisons & Décors
Méditerranée” - n°119 (Déc.
93-Janv. 94 - pp 80 à 85)
Bibliography
:
*01 -
Massot J.L. : Maisons rurales en Provence, Paris, Serg,
1975
*02 - Hanotaux G. : La Provence Niçoise, Paris, Hachette,
1928
*03 - Cadut-Narquet Ch. : Ajaccio, un patrimoine restitué,
BEE, Nice, 1992
*04 - Massot J.L. : L'esprit de restauration, Aix-en-Provence,
Areha
*05 - Steve M., Cadu-Narquet Ch. : Étude historique de l'architecture
toulonnaise, PRI, BEE, Nice
*06 - Rizza M. : Réparation de la pierre naturelle en Colloque
interrégional Afip, Nantes, 1993
*07 - Bossoutrot A. : La pierre mise à nu, in Lithiques
n°6, Paris, 1989
*08 - Inventaire Général des Monuments & Richesses
de France, Vocabulaire de l'architecture, Paris, Imp. Nationale,
1972
*09 - Documentation française du bâtiment : Les pierres
de France, Ed. du Moniteur, Paris, 1980
*10 - Triat J. M. : Pierres utiles de Provence, Cahiers de Documentation,
Ch. de Commerce et d'Industrie, Marseille, 1982
*11 - Cadu-Narquet Ch. : Étude chromatique de l'architecture
toulonnaise, PRI, BEE, Nice, 1992
*12 - Viollet-le-Duc : Entretiens sur l'Architecture, Paris, 1863,
Réed. Mardaga,
7ème entretien, p. 253, 1977
*13 - Sicof : La restauration du patrimoine pierre, Doc. Tech.
Sicof, Nantes, 1991
*14 - Virolleaud F., Laurent M. : Le ravalement, Paris, Ed. du
Moniteur, 1992
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