A7 Mud brick walls

Building
techniques :
Country:
A7 Mud brick walls
Portugal
PRÉSENTATION
Geographical Influence
Definition
Mud brick walls
- Denomination: brick/adobe
-Raw material : earth (mud / clay)
-Bricks are shaped / moulded before laying
-No baking : mud elements are dried in the
sun.
-Bricks are homogeneous in size and height,
laid straight
-Bricks are laid in mortar
Environment
The use of mud brick has been reported in all countries of the Mediterranean area, except Israel.
This building technique is found in all rural areas, in each country .It is sometimes but seldom found in urban areas in certain countries.
It is usually found in plains, but can occasionally be found in mountain areas or seaside areas.
In Portugal , mud brick masonry is found in rural and urban areas, in plain or mountain areas as well as seaside. Its use is quite common.
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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A7 Portugal – Mud brick walls
CONSTRUCTION PRINCIPLE
Foundations
Illustrations
Because mud has poor mechanical resistance and is poorly waterproof, the builder usually
lays a full length stone wall base prior to a mud brick wall construction. This foundation may
be quite small when the wall is built in rocky terrain. Otherwise, compact or masonry stone is
used.
In some cases, these foundations are extended above ground level, thus becoming an actual
wall base. More rarely, this type of wall is added to hewn-stone masonry, overlapping the
stone base.
In Portugal, contrarily to the other study countries where this technique is used, no foundation
preparation is necessary. The foundation is superficial and consists in leveling the ground
without bringing any resistant elements.
Building materials
Type and hardness :
The raw material used is more or less clayey earth, in association with variable proportions of
sand, chopped straw, gravel, stone or clay.
On the common scale fixed for this study (1=chalk 10=granite ), the hardness of mud brick is
reported as weak (1 to 3), and rarely average(4-5).
As this material is man made and not found in nature, its mechanical qualities directly depend
on the quality of: available earth, possible aggregates and brick-making process . Mud bricks
are even harder when the earth used is clayey. When chopped straw is added, the
fermentation process produces lactic acid increasing the material’s resistance.
In Portugal, earth is used without other raw materials: the adobe hardens with time. Without
stabilisation and after it is manufactured, it is a fragile material (very soft) - 1; when stabilised
with lime, it is slightly harder - 2 or 3.
Modules :
The modules are limited in volume. The average length of mud bricks made in the
Mediterranean area vary from 20–42 cm, height from 5-33 centimeters, depth from 10-36
centimeters. The average volume thus ranges from 1,5 DM3 (Spain) to 16 DM3 (Jordan).
The regularity of the volumes in a same series depends on whether they are made using a
mould or not.
Because bricks are handmade and produced locally, modules may vary considerably inside
the same country and the same series. Size may also vary between modules of the same
production.
In Portugal, modules vary and depend on the area and the type of wall:
Gandaraise – m. ext. (0.45x0.30x0.15) and m. int. (0.45x0.21x0.15)
Mértola – m. int. of the XIII th century (0.15x0.15x0.06) non structural, only partitions
(archaeological excavations).
Murtosa – " wall " adobe (houses) 0.30x0.40x0.10m " pigsty " adobe (annex buildings and
cattle pens) 0.25x0.40x0.10m " wall " adobe (fences) 0.20x0.40x0.10m " mendões " adobe
(interior partitions) 0.12x0.40x0.10m
Mortar laying
Realisation / Construction:
This technique is used for the building of one-face walls or two linked facing walls. It is only
exceptionally found for two non-linked facing walls .
Mud bricks are always laid in mortar. The mortar used is made of earth and various
aggregates in variable quantities ( more often : straw, sand, gravel ). The aggregates used
depend on the availability of raw material on the building site.
In Portugal, mud brick walls have only one facing.
Binding materials :
For all the countries studied, earth is used as binding material. It is sometimes combined with
lime (in Greece, Palestine, Portugal, Turkey).
In Portugal, the binding materials are earth, lime, aggregates and sand.
Construction principle :
moulds, modules and dimensions
Aggregate :
The aggregates and framework used are sand, gravel, chopped straw, organic fibers, in
different combinations depending on local availability.
In Portugal, the aggregate used is sand.
Construction principle : realisation
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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A7 Portugal – Mud brick walls
CONSTRUCTION PRINCIPLE (CONTINUED)
Mortar laying (continued)
Illustrations
Aggregate-grading :
The granularity of these aggregates depends on their kind and varies from 0-3 to 0-21
millimeters.
In Portugal, the grading for the mortar is about 0-3 millimeters.
Dose ratio :
The compositions vary from one place to another, sometimes privileging binding materials,
and other times aggregates. When lime is used in the composition, it’s dose is irrelevant.
In Portugal, 2 volumes of aggregates are used for 1 volume of binding material.
Thickness and Dimensions
The thickness of walls made of mud brick ranges from 40 cm minimum to 60 cm maximum.
In some rare cases, in certain countries, mud brick walls are 30 cm minimum, sometimes
even exceptionally 20 cm, and up to 80 cm maximum. Such walls are usually limited in
height, and in most cases are used for one floor only when wall thickness is under 30 cm.
Nonetheless, it is possible to build walls up to a maximum height of 8-10 m high, on a wall
base of an average 50 cm thick.
In Portugal, the average thickness is 55 to 60 cm, for a constant height according to level.
Mud brick dwellings can have 1 or 2 levels, often 2,5 or 5 m. high.
Finishing
Mud brick doesn’t resist atmospheric weathering well, and is very sensitive to humidity.
Protecting this type of wall is therefore essential to withstand ageing : coating or rendering are
reported in all the countries studied. The protecting materials are a rendering of earth or lime,
or an earth coating covered with lime-wash. The composition of the finishing coating can
vary. We find all the raw materials used in making brick: straw, gravel…
Bare walls are scarce, and only reported for annex buildings or surrounding walls.
In Portugal, mud brick masonry is rendered then painted with lime. Bare walls are also found
in Portugal, for additional buildings and surrounding walls. In the Gandaraise house, the back
and the interior court were neither rendered nor bleached with lime.
Tools
No specific tools have been reported by mud brick wall builders: traditional masonry tools are
the only ones reported . For brick making however, the use of moulds enables the making of
a series of homogeneous modules. Tools to level the bricks are sometimes used to squeeze
and tighten the earth in the moulds.
Extracting the earth is simply made with common tools: shovels, picks.
In Portugal, no specific tool is used for the implementation of the wall, besides those used to
manufacture the adobe.
Construction principle : finishing aspect
Trades
In all the countries of the Mediterranean area, it is the mason who makes and lays mud brick.
In rural areas, this technique is even sometimes implemented by the users themselves.
In certain countries, the mason gets his material from a brick maker.
In Portugal, it is the mason who makes mud brick walls.
Construction principle : Analysis
This project is financed by the ME DA 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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A7 Portugal – Mud brick walls
CONSTRUCTION PRINCIPLE (CONTINUED)
Thermal and Acoustic Performance
The thermal performance of mud bricks generally ranges from good to very good in the countries of the Mediterranean area. A mud brick wall’s
main quality is in the regulation of inside temperature, in a climate subject to great variations in temperature.
A mud brick construction is built with great attention to the thickness and mass of the wall thus giving it high thermal qualities. This type of wall
slows the penetration of heat during the day and retrocedes it usefully during the night.
The acoustic performances, ranging from fair to very good, vary according to the density of the raw materials used.
In Portugal, the thermal performances of mud brick walls are rated as good, with 0.46 A 0.81W/mºC, for a 0.40m thick wall. It is a bad thermal
conductive and an good insulator. Mud adobe houses are generally thermal delayers, which means that they react slowly to outside temperatures.
They heat or cool slowly, i.e. they are warm in winter if heated and fresh in summer. In the field of the acoustic insulation, the measurements are
50dB for a 0.40m wall, at 500Hz. Adobe is a bad acoustic conductive and an excellent insulator.
Ageing pathology
Linked to materials and climate conditions :
The encountered pathology is directly linked to the high solubility of mud. Good maintenance of the outside coating is essential. When the
coating deteriorates, mud masonry is directly exposed to the damage of rain waters, which leads to a quick deterioration of the pointing followed
by crumbling of the bricks themselves .
In Portugal, pathologies in these houses are frequently due to moisture: disintegration of the coating material and loss of thickness at the base of
the wall due to the joint erosive action of capillary moisture and salt efflorescence (pathology worsened by the absence of foundation and a direct
contact of themasonry with the ground); peeling of the rendering and dissolution of the earth that constitutes the walls. Joint action of rain, wind
and moisture by infiltration; wear, sometimes deformation of the top masonries, at the angles and lintels: erosive action of wind and water. In
addition, adobe has a reasonable resistance to compression, but cannot withstand concentrated loads; its flexural or traction strength is almost
null. Moreover, it suffers from greater brittleness in the presence of water, which diminishes the cohesion of clays.
Linked to techniques :
Generally speaking, no specific pathology linked to this technique has been reported. However, the quality of this kind of masonry depends on the
attention brought to the making and laying of the modules.
In Portugal, the structural pathologies related to the technique are: diagonal slits in the masonry caused by concentrated loads, sometimes with
partial crumbling close to eaves and lintels (more frequent than mineral masonries); loss of perpendicularity of the walls due to side strains
caused by the weight of the roofings and the floor, sometimes with sliding and crumbling at the angles; laying differentiated from foundations, with
vertical slits in the masonry due to movements in the surrounding zone or to a bad dimensioning of the foundation.
This project is financed by the ME DA 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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A7 Portugal – Mud brick walls
CONSTRUCTION PRINCIPLE (CONTINUED)
REALIZATION DESCRIPTION
Example in Portugal : (Text in French)
Conditions de réalisation :
La technique est utilisée dans des régions très chaudes avec peu de pluie en hiver, ce qui correspond aux conditions requises pour la mise en
oeuvre de cette technique.
Fabrication des éléments :
- Un an à l'avance, creusement d'un puits pour récolter les eaux
- Collecte sur le site des matières premières : terre riche en chaux, plantes sèches, cendrées et fibres de toutes sortes.
- La fabrication des éléments commence avec un temps d'avance pour permettre le séchage des briques avant leur mise en oeuvre (2 semaines)
- Les moules sont confectionnés ou achetés
- Les cadres des baies en bois sont réalisés en atelier par le charpentier
Travaux préparatoires :
- Le maçon met au point le projet avec le propriétaire
- Mise au point du projet avec ou sans support (plan schématique)
- Le maçon implante les axes des murs
- Creusement de la faille jusqu'à atteindre le bon sol
- Le maçon et les manœuvres fixent le niveau des fondations
- Les fondations sont réalisées en pierre brute et en mortier de chaux jusqu'au niveau de la première assise de briques
- Le maçon implante les angles, les cloisonnements et les ouvertures
Pose :
Le maçon fixe les niveaux et maçonne les briques au mortier, avec l'aide de son assistant
Les manœuvres mixent le mortier, approvisionnent le chantier en matériaux et continuent à collecter les matériaux
La pose des encadrements de baie en bois se f ait simultanément de manière à guider la construction des ouvertures
- La construction des murs est exactement pareille à celle décrite pour la construction des murs en briques mais de petites différences existent : Si
l’adobe est carré et non rectangulaire, l’angle sera exécuté au moyen de modules en adobe pour décaler les assemblages verticaux, et réaliser
la rangée impair ou pair. Il y a aussi quelques différences dans les mortiers. Le mortier utilisé est souvent la terre crue, de granulométrie
identique à celle qui est manufacturée en adobe., mais mélangée avec de l’eau jusqu’à atteindre l’état plastique. Dans certaines régions on
utilisait des petites pierres dans les joints de façon à mieux caler les adobes.
Une autre différence est le revêtement extérieur, en cas de maçonnerie en adobe, il n’était pas nécessaire d’attendre un an pour recouvrir les
murs des maisons d’enduit. L’adobe est un matériau déjà sec et l’enduit se faisait immédiatement après la finition des murs et du toit, ensuite
venait le blanchiment à la chaux.
Temps de réalisation :
200 briques de terre crue par jour.
Une habitation de 8 m x 8 m avec cloisonnement sur un niveau de blocs par jour.
Un jour d'attente pour la prise des blocs dans le mur.
Les ouvriers travaillent tous les jours pour qu'une couche de blocs sèche avant qu'elle ne soit fixée pour toute une habitation.
Les détails importants :
- Vérification des niveaux et de la verticalité
- Humidification des murs et protection contre l'ensoleillement direct pour permettre un séchage lent
- L'appareillage et le liaisonnement sont essentiels pour la qualité structurelle du mur
- Contrôle de la qualité de la matière première, du mortier
Moyens de vérification
- Contrôle du matériau utilisé pour les blocs, le mortier et la finition
- Contrôle de la qualité de la main d'œuvre
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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A7 Portugal – Mud brick walls
ASSOCIATED WORKS
Angles and Columns
Illustrations
Angles : Possible treatment in the technique, using the same materials
No specific processing of angles has been reported. Angles are harped (toothed), the same
elements as for the facing are used.
In Portugal, angles are built with adobe, exceptionally terracotta brick. The angle is usually
marked outside with a slightly protruding lime mortar, sometimes a pilaster.
Columns : Possible treatment in the technique, using the same materials
Columns are most often impossible to build with mud brick. The low mechanical resistance of
mud brick does not allow it to withstand heavy local loads.
In Portugal, constructions with mud brick pillars are possible, but with limitations linked to the
low mechanical resistance of the material. One does not find this solution in traditional
architecture.
Windows and Openings
Angles
Lintels and Arches:
A one piece wooden lintel is the most commonly found lintel for mud brick constructions
throughout countries of the Mediterranean area. The number of pieces of wood can change
depending on the type of wood available and the thickness of the wall.
Exceptionally, brick lintels, with or without relief arches, are used to make openings.
In Portugal, lintels are built with stone or wood - with or without relief arch, or with terracotta
brick - systematically with a relief arch.
Jambs:
Jambs are not processed in any specific way. They are often built in the wall itself, in the
same material and using the same technique. Jambs are toothed. In some cases, full
wooden frames have been reported. A frame combines a lintel, jambs and supports integrated
in a single element: the frame is built in the wall during construction.
In Portugal, jambs are generally processed like the wall course. They can also be built with
stone, or be materialised with plaster (relief doorpost).
Supports:
Non protruding supports are used for openings in mud brick walls throughout the countries of
the Mediterranean area.
Dimensions:
Mud brick walls do not allow for large openings or windows.
When these openings are only for ventilation, they are usually of very small size, (length:15
cm, height: 20 cm). The maximum dimensions generally reported for doors are: (width:100 to
127 cm – height: 210 to 300cm ).
In Portugal, dimensions for openings in mud brick walls range from 60 cm and 210 cm in
height, 70 cm and 100 cm in width.
Windows and openings
Associated Elements
Generally speaking, no specific associated elements have been reported for this kind of wall
in the Mediterranean area.
In Portugal, no associated element was reported for this type of wall.
Wall-r o o f C o n n e c t i o n s
No specific processing has been found for wall-roof connections. However, to protect the
wall, the roof usually has an overhang, variable in size , on the eaves, and sometimes on
gables for sloping roofs.
No specific connecting elements have been reported. The structure of the roof usually sits
directly on the mud brick wall.
In Portugal, cornices are common for the laying of eaves.
Wall-roof connection
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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A7 Portugal – Mud brick walls
USE, EVOLUTION AND TRANSFORMATION
Use
Types of building:
In most of the studied countries, mud brick are used for housing. This technique has seldom been reported for the construction of public
buildings, either official or religious. In most countries it is usually considered as a means of construction for humble houses.
The wide availability of materials and their low cost, combined with the rudimentary technical background needed, make this means of
construction well within reach of the users themselves
In Portugal, for external and inside walls: House of Murtosa, Gandaraise, house with a porch, smallholding house in the South of Tage. Inside
walls: urban in a row of buildings, house in Barrocal, urban house with roof-terrace.
Period when the technique first appeared. Period when the technique is in use – still used today or disappeared :
Throughout all the studied countries this technique has been reported as extremely ancient. Its use is so far back in time that it can’t actually be
dated. The use of mud brick has disappeared in most studied countries. This technique was still in use until the middle of the 20th century.
In Portugal, the origin probably goes back to the Phoenician period, in the IInd century BC. to the Ist century BC, with a great recent trend in the
XIXth and XXth centuries.
Reasons why the technique disappeared or has been modified :
The reason that explains the disappearing of this technique is the emergence of new, more performing materials.
The constraints in the preparation, protection and upkeep of mud brick walls and renderings generally explain why modern, easy-to-use materials
were preferred to traditional brick masonry.
In some cases, social and economic changes (industrialization, economic growth of the population) explain why this technique disappeared. The
users gradually profited from an easy access to substitution materials (concrete blocks, terracotta)
In Portugal, besides culture loss problems – zones of strong emigration and real estate speculation, the emergence of new materials and the
industrialisation of construction rendered this traditional material incompatible, considering the slowness of construction and the lack of labour.
Evolution / Transformation
Materials:
Mud generally remains confined in the poorest and the most isolated areas, or in the areas most associated to this technique for the
repair/restoration of prestigious buildings. The use of mud is gradually being replaced by hollow bricks or concrete breeze blocks bound with
cement mortar, all products which are easily available on the market. With these new techniques, the wall built in this form barely stands as a
filling-in associated with a bearing structure made of reinforced concrete (posts-beams structure). The hollow bricks or the manufacturated
concrete breeze blocks are not equaling mud from the point of view of their mechanical and physico-chemical features. On the other hand,
soliditywise, bricks and concrete breeze blocks are more resistant and long-lasting than mud, especially when facing streaming rainwater.
In Portugal, the material was transformed, from adobe earth it became lime and sand adobe, more resistant, later replaced with industrial brick.
The blocks of compressed earth (BCE) are equivalent industrial products, the difference is in the percentage of water. The manufacturing of BCE
is carried out in machines with drier earth, close to pisa, but with the dimensions of adobe, BCE is more stable and more resistant to traction and
compression. Although it exists in Portugal, it is little used. It is an imported French technique.
Technical aspects:
The actual wall is most often built between the bearing points of the reinforced concrete structure, as a two linked facing wall for hollow bricks, and
as a single face wall for the breeze blocks. The contemporary joints in cement mortar are usually much thinner than the ones in earth mortar.
In Portugal, the manufacturing of adobe was replaced by solid industrial brick. The production of BCE can be manual with a small compression
machine or mechanised and industrial.
Evaluating materials and replacement techniques:
On a s trictly economical plan and due to the fastness of production, the use of hollow bricks or breeze blocks is satisfactory. Nevertheless, the use
of this replacing technique is not conclusive when regarding thermal comfort. From the physico-chemical point of view, the reinforced concrete
frame suffers from major dilatation phenomena under great changes in temperature, and therefore generates craks in contact areas between the
filling masonry and the bearing structures in reinforced concrete (post-beam). From an aesthetic point of view, this replacing technique is not
convenient for old structures. In addition, these two structures are not mechanically compatible. These new techniques are mainly employed on
new constructions.
In Portugal, traditional houses are generally destroyed and replaced by new, bland and standard houses. We have noticed a recent development
of hollow brick masonry and reinforced concrete structures, or repairs on existing buildings: external coatings replace primitive lime materials with
cement mortar, water-based paint finishing. These techniques (particularly BCE) are not recommended on traditional bases, considering the
chemical incompatibility of materials. They are not used for new buildings.
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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