Building
techniques
A1 – Hewn stone wall (ashlar)
Country
Mediterranean Area
PRÉSENTATION
Geographical Influence
Definition
Hewn stone wall
- Traditional masonry tools: chisels, picks
and hammers.
- 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.
Illustrations
General views :
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 Mediterranean Space – Hewn stone wall
CONSTRUCTION PRINCIPLE
Foundations
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.
Building materials
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.
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.
Construction principle : general views
Construction principle : internal organisation
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 Mediterranean Space – Hewn stone wall
CONSTRUCTION PRINCIPLE (CONTINUED)
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.
Binding materials :
The two binders used for the realisation of ashlar masonry throughout the studied countries
are either lime, or earth.
Aggregate :
The aggregates are sand, gravel, broken tile and coarsely or finely chopped straw.
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.
Construction principle : preparation of
foundations and cutting of stones
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 aggregate
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.
Construction principle : realisation of the wall
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 Mediterranean Space – Hewn stone wall
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.
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.
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.
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.
T h e r m a l a n d A c o u s t i c P e r f or m a n c e
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.
Ageing pathology
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.
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.
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 Mediterranean Space – Hewn stone wall
CONSTRUCTION PRINCIPLE (CONTINUED)
REALIZATION DESCRIPTION
Example in Spain : Squared stone
Prerequisites :
The material used is dressed stone, which requires the presence in the area of a specialist craftsman to prepare it. This is a task which is usually
carried out in a workshop on the same site as the quarry to facilitate transport.
Materials:
Foundations : Large dressed stone blocks ; Aerated lime ; Sand
Wall : Ashlars. A variety of stones is used, normally chosen according to availability in the area ; Plaster or earth ; Sand ; Aerated lime
Tools:
Transport : Transport using a cart and animal traction
Realisation : Profiles ; Screed and plaster ; Lines ; Stone lifting tongs ; Wedges ; Lever ; Rule and level
Laying on a bed of mortar : Buttering trowel ; Brick trowel ; Wooden mallet
Laying with posterior joint fill : Pointing trowel ; Float ; Stiff brush and broom
Realisation :
Foundations :
The foundations are built with large dressed stone blocks and lime mortar
The surface of the foundations should be completely horizontal to avoid shearing forces.
Construction :
The walls are marked out using profiles and lines.
The first course of ashlars is laid, as explained below, on the basis of the scheme marked out.
A system of reference for the wall is set up. This involves fixing vertical screeds at the corners of the walls and at the faces, at a maximum
distance of 6 mm. The screeds are fixed at their base using plaster and some slabs or bricks.
The screeds are positioned so that when the line is attached to them, it is just a few millimetres from the plane of the wall. This distance
leaves space to fac ilitate the building process.
In the case of uniform courses, the depth of the course is marked in pencil on the screeds and the line is tied at this point.
At this point in the process, there are two methods for the construction of ashlar masonry: laying on a bed of mortar and laying with posterior joint fill :
1. Laying on a bed of mortar
Two masons lift the ashlar to be laid using lifting tongs and position it above its resting place. They lower it gradually until the block is a just a little
way from the stones below and the side stone. Another worker places four wedges, two in each face, between the lower course and the new
block, which is left to rest on the wedges. The wedges are positioned about four centimetres from the vertices of the block to avoid chipping it. The
position of the block is assessed. This involves moving the ashlar with the help of a lever to check, using a rule and level, that it is quite level and
forms an even plane with the course below. When doing this, it is important to make sure that the wedges do not come out. The reassessed block
is lifted using the stone tongs without moving the wedges. The bed and course are wetted and a bedding of lime mortar is applied, a little thicker
than the wedges. The block is settled onto the mortar so that its weight forces the excess bonding agent into the joints. The ashlar is tapped with a
wooden mallet to settle it in its resting place. The wedges ensure that the width of the joints is as planned. The trowel is used to fill in and
compress mortar in the head or vertical joint; in this case, the mortar is slightly more liquid.
2. Laying with posterior joint fill
The ashlar is placed in position and leveled using the same technique as for laying ashlars on a mortar bed. The bed and head joints and the
side joint are sealed with plaster or earth, using a pointing trowel, leaving only the top joint uncovered, to form an entry. This open joint is filled
with a more liquid lime mortar which is poured from a bucket in which it is constantly swirled around to make the mortar flow. The mortar is liquid
enough to reach all the joints. When the mortar has hardened enough, the wedges can be removed. The sealant of earth or plaster is removed
by rubbing with a stiff brush and a broom. It is very important to remove the wedges at the right moment. If they are taken out before the mortar is
sufficiently hard, the weight of the ashlar may force out the layer of mortar with a subsequent transmission of forces between blocks, with the
attendant risk that the concentration of forces at a given point could break some of the blocks. If the wedges are left in too long while other
courses are superposed, there is a risk that when the mortar retracts, forces are transmitted by the wedges. This concentration of forces could
cause blocks to break on their surface. The ashlars are pointed with lime mortar, which is compacted using the pointing trowel and the brick
trowel.
Observations :
Despite the laborious and specialized process involved in preparing the materials, the construction of ashlars is relatively simple in
comparison with other types of masonry.
Illustrations :
1. Setting out the wall and digging the trench.
2. Foundation shuttering.
3. Rough cutting of the stone.
4. Fine dressing of the stone.
5. Attac hing rules and guidelines to check that the courses are vertical and horizontal.
6. Laying the ashlar before assessing its final position.
7. Pouring the liquid mortar into the joints.
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 Mediterranean Space – Hewn stone wall
ASSOCIATED WORKS
Angles and columns
Angles:
Illustrations
Possible processing in the technique, by using same 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.
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.
Windows and Openings
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.
Angles
Windows and Openings
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 Mediterranean Space – Hewn stone wall
ASSOCIATED WORKS (CONTINUED)
Windows and Openings (continued)
Illustrations
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.
Supports
Non-protruding supports are most common.
illustrations of protruding supports.
Several countries reported and detailed
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.
Associated Elements
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.
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.
Windows and Openings
Associated Elements
Wall-roof Connections
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 Mediterranean Space – Hewn stone wall
USE, EVOLUTION AND TRANSFORMATION
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.
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.
Reasons why the technique disappeared or has been modified :
The reasons evoked for the disappearing of the rough stone technique are most frequently the appearance of new materials considered as easier
to implement; and the high cost of skilled, little requested labour, rarefies this process, and leads to a disappearing of the know -how, 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.
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.
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.
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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