A1 – Hewn stone wall (ashlar)

Transcription

Building
techniques :
A1 – Hewn stone wall (ashlar)
Country:
Syria
PRÉSENTATION
Geographical Influence
Definition
Hewn stone wall
- Traditional masonry tools:
and hammers.
chisels, picks
- 4, 5, 6 faces-sometimes 2 faces
- Stone laying with or without wedging.
- Stones are laid straight, regular size or not.
- Mortar laying.
Environment
In the MEDA area, ashlar is used in all environments: urban, rural, mountain, plain and sea side. It is often regarded as a noble technique,
through its fine workmanship and qualities, regarded as more urban than rural. Its is generally common.
In Syria, ashlar is regarded as a more urban rather than rural technique. It is common in cities and has recently developed in rural environments.
Associated floors:
In Syria, ashlar is associated with all floors except the basement.
Illustrations
General view:
Detail close-up:
This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States.
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A1 Syria – Hewn stone wall
CONSTRUCTION PRINCIPLE
F o undations
Illustrations
Finding a "firm base" or “good ground” is a preliminary for the builder. If rock shows on the
surface, the wall is built directly above. If not, all countries dig a small trench (~ 50 cm deep),
practically never deeper than 1m. the width can be equal to the thickness of the wall aboveground, but it can also be up to twice this thickness. Combination of 2 factors: width of the
trench and type of filling materials: adjustments and adaptation to each spot and ground. The
materials are always stony: the trench is filled with stones, generally linked with mortar. If the
module is small, the trench is broader. Several countries reported construction over ruins
used as foundation.
In Syria, the foundation is dug to the rock bed: the wall is built directly above. A trench varies
in depth from 10 to 70 cm. The width is approximately 1 m, but at any rate always larger than
the wall above-ground. The foundations are made up of rough stones or compacted stones,
laid in a mortar mixed with small angular stones.
Building materials
Construction principle: foundations
Type and hardness :
To build ashlar walls, you must avoid using stones that might flake. The first quality for stones
is also that they be easy to cut and face: that is why limestone is commonly used in the
thirteen studied countries. It is usually semi hard, around five on a scale from 1 to 10.
(1=chalk 7 = marble 10=granite ). After limestone, we find basalt (Cevennes in France, the
Jordan Valley in the Middle East) and finally sandstone (in Spain, France, Tunisia), or granite.
In Syria, the main construction materials are various kinds of easily cut lime stone: the quality
of the stones and ashlar used for foundations vary according to the type of wall (external or
interior). They are delivered in large modules and are usually cut in a workshop. For the
external façade, one can find a granular stone called "pomegranate seeds" it can be finely or
coarsely granulated.
Modules
Modules of all sizes can be found. Thus, throughout the Mediterranean area, blocks are 12 to
80 centimetres long, 8 to 40 cm high and 15 to 60 cm deep. Blocks may vary substantially in
volume from 2 litres to 100 litres. These blocks can non-the-less be handled by a few men.
This being an important characteristic for dressed quarry stone walls (rough for dressed
quarry ) as opposed to six faced ashlar. The following correlation has been observed: large
modules are usually soft stone and not very dense (Israel = 80 x 30 x 40, hardness 3), small
modules are harder and heavier stones.
In Syria,
- Small modules: 25X30 and 35 cm deep.
- Ashlar: 27X45 and 30-35 cm deep.
Construction principle: thickness and
dimensions
Construction principle: nature and hardness.
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C O N S T R U C T I O N P R I N C I P L E ( C O NTINUED)
Mortar laying
Illustrations
Realisation / Construction:
Ashlar walls are always laid in mortar. The ingredients generally found are: lime + sand
(sometimes + gravel or + broken tile or + crushed stone powder), earth + straw, earth alone.
In Syria, ashlar walls are always laid in mortar. The composition of the most common mortar
is: red earth with straw, this mixture "ferments" for 2 days before use. The mortar layer is
often from 2 to 3 mm thick.
Binding materials :
The two binders used for the realisation of ashlar masonry throughout the studied countries
are either lime, or earth.
In Syria, the traditional binding material used for ashlar is red earth, but the use of cement has
developed recently.
Aggregate :
The aggregates are sand, gravel, broken tile and coarsely or finely chopped straw.
In Syria, to reinforce and link the stones, the inside face of the wall is filled with a mixture of
red earth and small jagged stones. Outside jointing is made with a mixture of fine sand and
lime.
Aggregate-grading :
The grading of these aggregates varies according to their nature, from 0-3 mm to 0-6 mm,
and up to 12 mm in Israel and Jordan.
In Syria, the grading of the sand used for the mortar varies from 0 to 3 mm for jointings, from 1
mm to 1 cm for the filling between the two facings of the wall.
Dose ratio :
One volume of mortar contains from 15% to 50 % of binding material, lime or earth. Fat mortar
can be used (40% to 50% of binding material in the composition), depending on the aggr egate
used: if only one type is used, and if it is fine, than the volume of mortar binding is increased.
Exceptionally, a second or third aggregate can be added to thin down the dose ratio (20% to
33%). In this case the aggregate grading is more elaborate and integrates fine elements
(stone powder, ashes), average size elements (sand, broken tiles) and large elements (gravel,
chopped straw). This art of combining inert mass materials saves on binding material and
optimises its use.
In Syria, the dose ratio used for the mortar of this kind of stone is 70% red earth and 30%
straw.
Construction principle: tools
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CONSTRUCTION PRINCIPLE (CONTINUED)
Thickness and Dimensions
This construction technique leads to building thin walls: 25 cm (exceptional) to 45 cm, and very thick walls, 45 cm to 100 even 120 centimeters.
In the first case, the stones on each facing of the wall are fitted one against the other, alternating one long with one short. In the second case, for
thick walls, the stone facings are separated with filling. This filling can be made of smaller elements of the same type: rubble, quarry waste, broken
tiles or broken bricks etc., or mortar alone. Sometimes header binder will joint two facings more efficiently. Sometimes the builder makes the wall
wider at each floor level. This traditional type of wall makes it possible to construct substantially high buildings (16 m or more). The corresponding
thickness can vary by 10% (60 centimeters for 6 m in height ) up to 50% (75 cm for 15 m in height). Up to four levels, 60cm are enough, beyond
we find a thickness of 80 to 120 cm. Common constructions do not have more than six levels. Greater heights are exclusively found in urban
areas.
In Syria, the external wall is high, with a thickness about 70-80 cm, it is a wall with two stone facings, each about 30 cm thick. The empty gaps
between them are filled with earth, lime and ashes. The outside facing of the wall is made with cut granular "pomegranate seed" stones, whereas
the interior facing is made with ashlar. The maximum height of an ashlar construction is 4 m in a rural area, 8 m in an urban area. In an old
downtown this is related to the width of the streets of certain Syrian cities.
Finishing
Four solutions for the finishing: bare wall, wall simply whitewashed, wall entirely rendered and wall rendered and whitewashed. Besides Portugal,
all the countries indicate that ashlar masonry - homogeneous and regular - remains generally apparent, at least outside. There are two distinct
reasons for choosing finishing coating: The first is aesthetic : giving priority or not to the regularity and homogeneous aspect of the facing leads to
leaving the wall bare, painting or rendering it. The second reason is practical. The rendering is a means of protection for the facing of the wall.
The choice noticed today is not necessarily the original one, it may have varied in time through restoration campaigns led for maintenance
reasons or influenced by style and fashion.
In Syria, the inside masonry is protected with a lime rendering, about 2-3 cm, in three layers:
- The base: 25% earth and ash, 25% wood ash and 50% chalk with a little red earth and water. The mixture is left to rest for 3 days.
- Fine rendering: 2/3 lime powder + 1/3 of hemp, stone powder and soap. The mixture is left to rest for 3 days. From the outside, the joints of the
horizontal and side walls are filled with lime mortar (lime powder, earth and ash).
Tools
In addition to traditional mason tools (wheel barrow , trowels, brush, plumb line, chisels, float, drift pins etc.), the traditional tools of the stone cutter
are necessary to prepare the stones. Besides, lifting tools (lewis, stone lifting bolts, pulley blocks, grips, levers...), wedges and thick glue are
needed.
Syria is renowned for the quality of its stone masonry.
Several tools are used: Hammer for hammering, chisels, granulating hammer, pick: to shape the "pomegranate seed" effect, sledgehammer: to
break large stones, concave pick, angle piece tool and measuring tape, pickaxe: to dig, shovel: to collect the earth, bucket to evacuate the earth,
brick trowel for mortar, levelling tool, plumb line.
Trades
In each country, masons can build this type of wall. However, this technique is a stone cutter speciality, who can make up to 6 faces. Sometimes,
a first man cuts the blocks in the quarry and then mason carries out the laying.
In Syria, this type of technique calls upon a mason builder and a stone cutter, as well as an assistant workman to carry the materials and a
workman to prepare the mortar.
Thermal and Acoustic Performance
For ashlar constructions, limestone is most commonly used (followed by basalt, sandstone, and granite) : the thermal and acoustic performances
are reported from good to very good by all the studied countries. The ingeniousness of the builders developed ventilation systems : they vary the
thickness and thus the mass of the walls, according to the nature of material used, producing the greatest possible inertia. This was naturally
sought to obtain a maximum thermal comfort for dwellings, dimming temperature amplitude between hot and cold seasons, day and night, which
can often be quite significant in the Mediterranean area. This mass also improves acoustic quality.
In Syria, the thickness of the walls (70 cm) produces maximum thermal comfort for dwellings, this is especially important as temperature amplitude
is significant between hot and cold seasons, as well as day and night. These walls also have high acoustic qualities.
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Thermal and Acoustic Performance
Linked to materials and climatic conditions:
For ashlar construction, pathology is very much linked to the stone used, and whether it is more or less porous, thus more or less sensitive to the
attacks of water and salts. Generally, rain water infiltration and capillary increase seem to be the main causes of disorders or deterioration noted:
deterioration of the pointing mortar, specific masonry disjointing, hollowing out in evaporation pockets for porous stones. The other forms of
moisture which deteriorate the masonries are little evoked by the partners, particularly splashing at the foot of wall and condensation. Moreover, a
lack or slack checking of the state of piping, drainage, wells, cisterns are reported as worsening factors.
In Syria, ashlar techniques are sensitive to water, moisture and salt. Water infiltration and capillarity are the main causes for damages:
deterioration of the mortar or jointing and swelling or compressing of the wall.
Linked to the technique:
No ageing pathology linked specifically to the ashlar technique was reported. In the event of faulty header binders with vault thrust, one can
however see a separation of the two rows of stones.
In Syria, nothing specific was reported besides Mediterranean commentary.
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R E A L IS A T I O N D E S C R I P T I O N
In Syria :
In Syria, the foundation is dug form a 1 to 7 m deep, or up down to the rockbed. The width does not exceed 1m but is always wider than the wall
above ground. The wall is built directly from this trench.
The foundation is made up of rough or compacted stones, laid in mortar containing small sized jagged stones.
Walls are high, thickness varies from 70 to 80 cm, with two stone facings, each 30 cm; gap between the two is filled with earth, lime, crushed
pottery, ash and rubble. The external facing of the wall is made with granular ashlar, whereas the inside facing is made with squared stones.
The stones must first be placed per row, larger facing placed horizontally and levelled with a string. This is to ensure well adjusted alternate joints.
The mortar acts as binding material.
The stones of the external walls are cut so the smooth side faces outside and the rougher side faces inside. This applies to the walls for inner
courts: the smooth facing is on the courtyard, and the rough side towards the rooms.
Concerning non load bearing walls, they are made with stone in the same way described, usually rendered inside and pointed outside. Sometimes
walls are built in a wooden framework then filled with earth: the wall is then rendered.
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A S S O C I A T E D WO R K S
Angles and columns
Angles:
Possible processing in the technique, by using same
Illustrations
materials
Generally, no specific processing of the angles was reported for ashlar constructions. It is
generally noted that the angle masonry is reinforced with an anchoring with larger module
blocks than those used for the walls. Sometimes, they are more carefully cut so as to obtain
more regular faces to ensure a better course and a cleaner edge to mark the right angle. The
same stone or another kind of stone, harder than that of the walls, is sometimes used. This
material change also shows an aesthetic concern, playing with the contrast of colours
between the masonry of the walls and the angles. When constructions are protected with a
rendering, the angle can stand out with a different tonality or finishing than the rendering.
Decorative elements (posts, carved stones...) are sometimes integrated.
In urban environment, that the ground floor wall angles are frequently chamfered to 45° or
rounded so as to ease traffic in the very narrow lanes.
In Syria, there is generally no specific processing for stone construction: angles are processed
the same way as the wall. The blocks of stone are the same size as those used for the
construction of the wall. Cases where the angles of the walls are rounded or chamfered at 45°
are less common.
Associated works : cut angle
Colunms: Possible processing in the technique, using the same materials
Ashlar stone used for the walls, generally allows for pillar construction when it is sufficiently
hard to withstand the loads. All alternatives are found: in the same modules as blocks,
quadrangular or round, in solid stone or paving + filling. The thickness of a pillar is seldom
under 60 cm.
Associated works :
pillars, columns with decorated capitals
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ASSOCIATED WORKS (CONTINUED)
Windows and Openings
Illustrations
Lintels and Arches:
Lintels and arches are found everywhere in the MEDA area.
Several types of lintels are met: 1 Single element, rough or squared wood element, branches
juxtaposed lengthways, monolith stone more or less well squared, sometimes carved. It
crosses the width of the opening and rests on the jambs. 2 Separate elements, stone or brick
arch.
It can be surmounted with a relief arch (or exceptionally as a “bâtière”) made up of several
stone or brick elements which better defer loads on the jambs.
Practically each country exploits three solutions: Single element lintel (stone or wood), with or
without relief arch, the arch in separate elements, round or flat elements. In many cases, the
lintels are mixed: stone on the outside of the wall, wooden on the inside face.
In some countries, like Cyprus, France, Greece and Portugal, lintels are made with terracotta
brick with or without relief arch. Jordan and Palestine only reported stone for lintels.
In Syria, openings are variable in size and the top side can be straight, curved or angled. The
high part of the opening must be given special attention as it must withstand loads and
transfer them to the lateral sides. The higher part of the opening is called "Najafa" and the
lateral sides " thighs ". Several variable lintels were reported on old buildings in Alep: the one
piece straight lintel made of a single stone element or a piece of wood laid on the sides, then
constructed upon. Lintels made up of several stones can still be found, they are called "open
right" whose resistance is based on the solidity of its stones shape. One can also find lintels
arch shaped with a slight curve for architectural purposes, as well as semi pointed "Persian"
or horse shoe shaped.
Theses stone elements are often used in odd numbers, so that the median stone, "the key"
(locally called "the lock"), is in the centre. The other stones bearing on the sides are subject
to great pressure and can also affect the other stones. For higher openings (doors or
windows), stone is used for the outside part of the lintel. The inside lintel is made of wood; 5
cm higher, wooden beams are laid across the width of the opening. They are then covered
with a thin wooden section called "Tawan".
Jambs
The jambs are generally assembled in the course of the wall, with same material and the
same technique. They sometimes consist of one or more stone elements, carefully cut with
sharp edges, protruding or not, sometimes profiled or carved, protruding or not on the
masonry. A structural body, the jamb sometimes consists of harder stone, sometimes even of
another type of stone. Changes of material and consequently of colour are undoubtedly also
an aesthetic concern. A rendering rarely covers the framing masonry of the opening. This
does not apply when jambs are made with ashlar.
In Syria, jambs are a structural body generally assembled within the very wall course, using
the same materials and the same technique. They consist of one or more stone elements, cut
carefully with a sharp arris, harped or not, sometime carved, protruding or non protruding. It is
sometimes made with a different type of stone or a different colour for aesthetic reasons.
Supports
Non-protruding supports are most common. Several countries reported and detailed
illustrations of protruding supports.
Associated works : lintels and arches
Dimensions
The technique of ashlar construction does not impose any specific constraints for openings.
The opening is generally a vertical rectangle. Its dimensions can vary in width from 10 cm
minimum to 200 cm maximum and, from 15 cm to 300 cm maximum in height.
From ventilation openings to barn doors, the width/height ratio is 1/2 to 1/8, sometimes 2.
In Syria, the ashlar construction technique does not impose any specific constraints
concerning size for openings: they can vary, whether for doors, windows or arches. The
builder always takes the proportions into account, as they play an aesthetic role and make the
very beauty of a building.
Associated works : supports
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ASSOCIATED WORKS (CONTINUED)
Associated Elements
Illustrations
In the MEDA area, Algeria, Portugal and Turkey describe corbelled volumes on the façades.
Later added balconies, buttresses, protruding elements, circulation galleries on the 1st floor of
dwellings, overhanging support trunks for floors or roofs, and waterspouts through acroters
are the main associated elements mentioned by the partner countries.
In Syria, wooden is used for corbelling elements fixed on the façade of a building, They can
be “ Kicks” used as a balcony.
Wall-r o o f C o n n e c t i o n s
In the MEDA area, when the roofs are sloped, dressed quarry stone runoff walls are generally
protected with an overhanging roof, variable in length (rafters, boards supporting /
withstanding roofing material). Almost everywhere, flat stones, fired brick or stones are
reported, laid in corbelling on the top of the walls. For flat roofs, either the wall is prolonged
with a more or less high acroter, thus enclosing the flat roof, the roof protection rendering falls
overhangs onto the higher part of the external walls, or a system projects rainwater away from
the walls.
In Syria, for urban ashlar constructions, walls extending into stone crownings or cornices to
enclose roof terraces have been reported. On the other hand, in rural environment no roof
connection element has been reported.
Associated elements : kishk
Wall - roof connections (cornice)
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U S E , E V O L U T I O N AND T R A N S F O R M A T I O N
Use
Types of building:
The ashlar wall is especially used for commissioned architecture, religious buildings, military structures, noble and middle-class houses, or private
mansions. According to areas, the availability and the hardness of local stone makes this technique practical for apartment buildings and
annexes.
In Syria, ashlar walls are used for dwellings and public buildings. Local stone availability made its use common for all buildings.
Period when the technique first appeared. Period when the technique is in use – still used today or disappeared :
This technique has been used since Antiquity, during which it disseminated widely. It is still used nowadays, particularly for the rehabilitation of
certain historical buildings.
In Syria, this technique has been used since antiquity and is still common today in the construction and restoration industry. However, the stones
used today are thinner than before.
Reasons why the technique disappeared or has been modified :
In the MEDA area, the reasons evoked for the disappearing of the rough stone technique are most frequently the appearance of new materials
considered as easier to implement; the high cost of skilled, little requested labour, rarefies this process, and leads to a disappearing of the knowhow, from the construction technique point of view as well as maintenance.
Evolution / Transformation
Materials:
To a certain extent, far from the original technique, ashlar is being replaced with the cast agglomerate blocks (cement blocks, air concrete,
terracotta) on wide trade-networks. These blocks are identical in terms of module, but undergo a specific process for the angle, lintels and other
elements. They are assembled with a variable width, including reinforced concrete hardeners. In certain cases, particularly in the Middle-East,
stone plating imitates the aspect of the traditional technique.
In Syria, non-load bearing inside walls are built with cement breeze blocks, the rendering mortars contain cement.
Technical aspects:
This kind of building does not require much tooling. Today, mechanical means help for handling, supplies, transport and lifting. The mortar is
mixed in a concrete mixer. Laying modern materials is similar to stone laying.
In Syria, machines are used for the preparation and cutting of ashlar, as well as for handling. Traditional means of construction have been
maintained in old cities.
Evaluating materials and replacement techniques:
-Materials are reliable for conservation if they can withstand the loads. Resistance may vary according to the kind of materials used:
(Cement/terracotta/porous concrete), difference in width, and depending on if materials are hollow or full. This also applies to building
transforming.
-These materials are much more economical than traditional stone masonry.
-Depending on the materials chosen there can be a substantial difference as far as thermal insulation is concerned. Width also influences
performance.
Thermal insulation can be added at the same time.
-As regards aesthetics, the issue is related to thickness: older buildings are 0.60m wide or more and this is very obvious for openings (windows
and doors).
-For old buildings, replacing with modern blocks is only satisfactory if masonry is then coated with finishing.
-For new buildings, particularly private houses, these replacement techniques are no longer used.
In Syria, replacement materials and technique have speeded up construction but had an effect on the solidity of some elements in ashlar
buildings.
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A1 – Hewn stone wall (ashlar)

Transcription

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