1cfb5bf-CIS888614800299410

(1)

EARTH BUILDING

History, science and conservation

 

Paul Jaquin and Charles Augarde

(2)

(3)

(4)

History, science and conservation

EARTH BUILDING

(5)

(6)

History, science and conservation

Paul Jaquin and Charles Augarde

EARTH BUILDING

(7)

Published by IHS BRE Press

IHS BRE Press publications are available from www.brebookshop.com

or

IHS BRE Press Willoughby Road Bracknell RG12 8FB Tel: 01344 328038 Fax: 01344 328005 Email: [email protected]

Printed on paper sourced from responsibly managed forests

Requests to copy any part of this publication should be made to the publisher:

IHS BRE Press

Garston, Watford WD25 9XX Tel: 01923 664761

Email: [email protected]

The authors and publisher accept no responsibility, nor liability, in any manner whatsoever for any error or omission, nor any loss, damage, injury, or adverse outcome of any kind incurred as a result of the use of the information contained in this book or reliance upon it. Readers are advised to seek specific professional advice relating to their particular construction project and circumstances before embarking on any building work.

Reasonable care has been taken to ensure the accuracy of the information in the book at the time of printing. Drawings and technical details are indicative and typical only and final detailing for any project remains the responsibility of the designer. The publisher accepts no responsibility for the persistence or accuracy of URLs referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.

EP 101 © Copyright Paul Jaquin and Charles Augarde 2012

First published 2012 ISBN 978-1-84806-192-7

Front cover images:

Left, Rammed earth, Kasbah Caid Ali, Asslim,

Morocco

Top right, Adobe bricks drying, Aït Ben Haddou,

Morocco

Middle right, Cob toilet block, Melon car park,

Eden Project, Cornwall, UK. Courtesy of Jackie Abey and Jill Smallcombe, Abey Smallcombe cob builders

Bottom right, Rammed earth barn, Villafeliche,

Spain

Back cover image:

Lime-rendered cob house, Devon, UK Index compiled by Paul Nash

(8)

PREFACE v

PREFACE

This book is the result of research carried out at Durham University, and subsequent work at historic earthen sites around the world. Paul Jaquin undertook a PhD supervised by

Dr Charles Augarde, and the research shed light on the important mechanisms behind the mechanical behaviour of earthen construction. We believe this research is the first to view earth buildings in the framework of unsaturated soil mechanics, and we show that, by doing this, many aspects of the behaviour of earth buildings can be explained better. By appreciating the unsaturated nature of earth buildings, it is possible to understand the changes in behaviour of earth buildings and the causes of damage, and therefore to develop successful restoration strategies.

We have focused specifically on the

conservation of historic earth buildings, but the principles outlined are equally applicable to modern earthen construction. We have included a section on the history of earth building to allow readers to place buildings within a historical and geographical context.

Although much of the research focused on the conservation of historic rammed earth, the underlying principles are common to all types of earth building, and while the damage and conservation techniques are also inclined towards rammed earth, many of the damage and repair

strategies are independent of the type of earthen construction.

This book is written for engineers, conservation professionals, and those interested in earth buildings. As earth is such a varied material, and many aspects

of earth building are based on experience, the book does not generally provide specific values (for example for strength or stiffness), or rules of thumb for earthen construction and restoration.

There is still a great deal of work to be undertaken before understanding of earth

building reaches the levels of more conventional building materials such as steel and concrete. Further research is required into earth buildings at all scales, from investigation of the interparticle contacts to the development of codes of practice and standards. Of particular interest are the

behaviour of earth buildings in earthquakes (which is not covered in this book), the exposition of archaeological sites, and the thermal behaviour of earthen buildings. Earth is becoming increasingly popular as a sustainable construction material, and it is hoped that this book will lead to improved scientific and engineering understanding of earth as a construction material.

Paul Jaquin Charles Augarde November 2011

(9)

ACKNOWLEDGEMENTS

�

Thanks must go first to Professor Chris Gerrard

of the Department of Archaeology at Durham University, who first wondered whether the large cracks in a building he was studying in Spain were a problem, and who really set this line of research going. Thanks also to Professor David Toll of the School of Engineering and Computing Sciences at Durham University, who on viewing an early experimental rammed earth wall in the civil engineering laboratory, noted that it ‘looks like suction’. We also thank Nick Clarke, Publisher at IHS BRE Press, whose vision for the publication of this material has finally come to fruition.

Many students at Durham University have been involved in earth-building research, and have helped us understand these materials through their work, specifically Chris Beckett, Cynthia Hendy, Tom Horncastle, Tom Howard, Steven Perkins, Jenny Durie, Lucie Le Grand and Jacinto Canivell. Thanks to those with whom we worked on developing this field at Durham, namely Dr Sergio Lourenço (now at Cardiff University) in the field of unsaturated soil mechanics and Dr Cathy Clarke (now at Stellenbosch University) for help with the chemistry.

Paul was privileged to undertake a Research Associate role at the University of Bath during the

summer of 2008, and thanks go to Professor Peter Walker, Dr Andrew Heath and Dr Enrico Fodde at University of Bath for their discussions and support during this period of research. Thanks also go to Manfred Fahnert, organiser of the Lehm Express in Morocco, who taught Paul to clay plaster.

Parts of the research overseas have been undertaken with the aid of travel grants from the Institution of Structural Engineers and Engineers without Borders for visits to India and Bhutan.

Thanks go to members of the ICOMOS International Committee on the Conservation of Earthen Architecture for their expertise and support, and to Paul’s colleagues both in the UK and in Sweden, for their support and interest in this non-conventional building material. Thanks also go to those who have supplied photographs which has enabled us to show a much wider range of earth building.

Finally, for help, support and enthusiasm, and for being dragged on earth-building-related ‘holidays’ for many years, thanks go to Paul’s girlfriend, Eleanor Trueman.

(10)

CONTENTS vii

NOMENCLATURE

�

CEB Compressed earth blocks CSH Calcium silicon hydrate OWC Optimum water content RH Relative humidity

SWRC Soil water retention curve Apparent cohesion

F Force

Attractive force due to surface

F _tension

tension

F _pressure Attractive force due to pressure

difference

g Acceleration due to gravity h Relative humidity, height

N Normal force

p₀ Pressure of saturated water vapour p_v Pressure of water vapour

R Universal gas constant

r Radius

r_neck Radius of the neck of a liquid bridge r_x , r_y Radius of curvature of meniscus S_r Degree of saturation

s Suction

T Temperature

T _s Surface tension

u Pressure, pore water pressure u_a Air pressure

u_w Water pressure

v_w Molar volume of water

θ Contact angle

μ Coefficient of friction ρ d Dry density

σ Stress, total stress σ ′ Effective stress

τ Shear strength

φ Macroscopic friction angle

(12)

1 INTRODUCTION

INTRODUCTION

�

Earth buildings are perceived by many as simple ‘mud huts’, liable to damage, and earth as at the bottom of the list of desirable construction materials. While earth buildings are more liable to damage by water than those constructed from other construction materials, earth is one of the simplest and most sustainable construction materials, and many of the oldest structures in the world are constructed from this material. Around 30% of the UNESCO World Heritage Sites are constructed from earth.

In common with buildings made from all other types of construction materials, historic earth buildings are liable to damage, through lack of

maintenance to protect against the weather, changes to the local environment, or damage caused by external factors. This book aims to present the reasons for the occurrence of such damage, and to provide strategies that may be useful in the conservation of historic earth structures. We do this by providing a scientific rationale for the behaviour of earth buildings. By viewing earth buildings in the framework of unsaturated soil mechanics, we are able to better understand their behaviour, and thus the damage that earth buildings may suffer.

The book begins with an introduction into the different types of earth building, and we argue that although the construction techniques are markedly different, there are definite common themes that apply to every type of construction material. In Chapter 2 we briefly describe the history of earth building, using some of the main archaeological and architectural sites worldwide. This serves to allow the reader to place any structure under investigation into an international and chronological context. The principles of general and unsaturated soil mechanics are outlined in Chapter 3. Relatively recent research

findings allow for an improved understanding of the mechanical behaviour of earth buildings, and in Chapter 4 we show how this relates to observed damage mechanisms in earth buildings. Finally, in Chapter 5 we present mitigation and repair solutions that may prove useful in the conservation of historic earthen sites.

This book is not a practical guide on earthen construction, nor is it an engineering textbook. Techniques for different types of earthen

construction can be learned from numerous sources, both through practical courses and through guides. A history of earth building is provided that focuses

on some main sites, although many are not included for brevity, and the history of specific earthen sites is not explored. The principles of unsaturated soil mechanics are explained, but there are many logical steps that are not included, and reference should be made to our journal papers and to other engineering textbooks. As earthen construction is so varied, and as there is a much smaller pool of test data than for other, more conventional construction techniques, specific values for soil testing and mechanical properties are not given. We do not provide information on field or laboratory techniques for the testing of earthen materials. Engineering analysis methods for structures are not explained, and the advice of a competent engineer should always be sought when considering the conservation of historic earth buildings.

Finally, the behaviour of earthen buildings in earthquakes is not specifically discussed. This behaviour is complex, and although the damage mechanisms are similar to those described in this book, we do not deal with these, or with the retrofitting or reconstruction of earth buildings after seismic events.

(13)

(14)

3

TYPES OF

TYPES OF EARTHEN CONSTRUCTIONEARTHEN CONSTRUCTION

CHAPTER 1

CHAPTER 1 TYPES OF

TYPES OF

EARTHEN C

ONSTRUCTION

�

1.1

INTRODUCTION

Earth is one of the simplest construction materials, Earth is one of the simplest construction materials, and all earth buildings have the same basic

and all earth buildings have the same basic constituent parts: soil

constituent parts: soil from the ground, and from the ground, and water.water. These are mixed together and formed into shapes, These are mixed together and formed into shapes, and then water evaporates to leave an earthen and then water evaporates to leave an earthen structure. Other materials can be added to the structure. Other materials can be added to the mixture, either to help with production, or to mixture, either to help with production, or to improve the mechanical properties of the finished improve the mechanical properties of the finished product. Soil types, construction techniques and product. Soil types, construction techniques and building traditions vary greatly across the world, and building traditions vary greatly across the world, and many techniques are variations and combinations many techniques are variations and combinations of those described below. There are many ways to of those described below. There are many ways to form earth into structures, but this book deals with form earth into structures, but this book deals with techniques where earth is the major constituent techniques where earth is the major constituent material. The techniques are split into two classes: material. The techniques are split into two classes: those in which independent units are constructed, those in which independent units are constructed, dried, then transported and laid to form a structure dried, then transported and laid to form a structure – namely adobe and compressed earth blocks; – namely adobe and compressed earth blocks; and those where homogeneous monolithic and those where homogeneous monolithic

constructions are produced in situ, such as cob and constructions are produced in situ, such as cob and rammed earth. This book does not discuss building rammed earth. This book does not discuss building techniques where earth is only a secondary material, techniques where earth is only a secondary material, and therefore wattle and daub, rammed tyres and and therefore wattle and daub, rammed tyres and earth bag construction, or stone and turf buildings earth bag construction, or stone and turf buildings are not discussed.

are not discussed.

1.2

EARTHEN CONSTRUCTION PRINCIPLES

All earth construction follows the same basic All earth construction follows the same basic principles. Soil is taken from the ground and principles. Soil is taken from the ground and mixed with sufficient water to allow moulding and mixed with sufficient water to allow moulding and placement. Most of this water then evaporates, placement. Most of this water then evaporates, leaving the soil in a new state. In wholly unstabilised leaving the soil in a new state. In wholly unstabilised earthen structures (from sandcastles to the Great earthen structures (from sandcastles to the Great Wall of China) this water forms into bridges between Wall of China) this water forms into bridges between particles in equilibrium with the

particles in equilibrium with the surrounding airsurrounding air, and, and it is these bridges that provide a major component it is these bridges that provide a major component

of the additional strength compared with completely of the additional strength compared with completely saturated or completely dry soil.

saturated or completely dry soil.

In many forms of earthen construction, other In many forms of earthen construction, other materials (called stabilisers) are included in the earth materials (called stabilisers) are included in the earth mixture. These combine physically or chemically mixture. These combine physically or chemically with the soil, and are included to improve the with the soil, and are included to improve the mechanical properties of the structure (for example, mechanical properties of the structure (for example, straw or hair to improve tensile capacity and reduce straw or hair to improve tensile capacity and reduce shrinkage cracking, or cement to improve the shear shrinkage cracking, or cement to improve the shear strength), or to improve the workability of the earth strength), or to improve the workability of the earth mixture (for example urine), or to provide water mixture (for example urine), or to provide water repellency (for example bitumen or silicone). repellency (for example bitumen or silicone).

All forms of earthen construction follow similar All forms of earthen construction follow similar initial steps:

initial steps: 1.

1. Soil is first dug from the ground. This soil shouldSoil is first dug from the ground. This soil should be taken from below the topsoil, and ideally be taken from below the topsoil, and ideally from above the water table. Where earthen from above the water table. Where earthen construction is common, there may be construction is common, there may be well-known deposits of suitable soil that can be known deposits of suitable soil that can be utilised (Figure 1.1).

utilised (Figure 1.1).

Figure 1.1:

Figure 1.1: T Taking suitable soil from next to the aking suitable soil from next to the site of asite of a

wall. Jomsom, Nepal

1 1

(15)

2.

2. The correct proportion of water to be added toThe correct proportion of water to be added to the soil depends on the construction method, the soil depends on the construction method, particle size distribution, and compactive effort particle size distribution, and compactive effort to be applied. If the soil dug is too wet, it may to be applied. If the soil dug is too wet, it may be spread on the ground to allow pore water be spread on the ground to allow pore water to evaporate. If the particle size distribution to evaporate. If the particle size distribution is not correct for the construction type, then is not correct for the construction type, then the soil may be sieved to remove particles the soil may be sieved to remove particles that are considered too large. This sieving that are considered too large. This sieving can be done by manually removing larger can be done by manually removing larger stones, or by passing the soil through a mesh stones, or by passing the soil through a mesh of fixed aperture. This is best achieved using of fixed aperture. This is best achieved using a frame, as shown in Figure 1.2. In order to a frame, as shown in Figure 1.2. In order to manufacture the correct soil mix, different soils manufacture the correct soil mix, different soils are combined.

are combined. 3.

3. Water and any additives are then mixed intoWater and any additives are then mixed into the soil

the soil in defined in defined proportions. Traditionallyproportions. Traditionally,, the soil is piled into a cone, with water poured the soil is piled into a cone, with water poured into the centre. The soil is then mixed in with into the centre. The soil is then mixed in with the water by people or animals walking around the water by people or animals walking around on it (Figure 1.3), or by shovelling the earth on it (Figure 1.3), or by shovelling the earth into the water until all the water is mixed in. into the water until all the water is mixed in. Alternatively a rotary mixer (Figure 1.4)

Alternatively a rotary mixer (Figure 1.4) can becan be used. When conserving earth buildings, the used. When conserving earth buildings, the type and function of additives placed in the type and function of additives placed in the original structure should be well understood original structure should be well understood before further additives are used.

before further additives are used.

When the soil, water and additives have been When the soil, water and additives have been combined to a homogeneous mixture, it should combined to a homogeneous mixture, it should immediately be formed using the techniques immediately be formed using the techniques described below.

described below.

Figure 1.2:

Figure 1.2: Sieving soil using a m Sieving soil using a mesh frame. Asslim,esh frame. Asslim,

Morocco

Figure 1.3:

Figure 1.3: Mixing earth with straw and water by Mixing earth with straw and water by

walking. Asslim, Morocco

Figure 1.4:

Figure 1.4: A rotating drum mixer that can be used A rotating drum mixer that can be used

to mix

to mix earth and earth and waterwater. Civil . Civil Engineering LaboratoryEngineering Laboratory,,

Durham University

(16)

5 TYPES OF EARTHEN CONSTRUCTION

1.3

MONOLITHIC EARTH WALLS

1.3.1 Rammed earth

The term ‘monolithic’ refers to an earth wall that is constructed in situ, and which functions as a homogeneous wall. There are two basic types: walls formed using formwork (rammed earth) and walls formed without formwork (cob).

Rammed earth uses a mixture of clay and sandy soil mixed with water and then compacted within formwork to form a monolithic earth wall. Earth is compacted between the formwork in layers until the formwork is filled. The forms are then moved to another location so that another section of wall can be constructed.

Rammed earth is known as:

• tapialin Spanish, andtapia in Portuguese, which

are corruptions of the Arabical taub

• pisé (or pisé du terre

the Latin verb pinsere

• hāngtŭ ( ) in Chinese.

silt [1]_{, and if the mixture is to}

sandy soil should be used[2]_.

Silt Sand Gravel

1 2 10

Figure 1.6: Master mason Malem with rammed earth formwork. Asslim, Morocco

This is the arabic for ‘al taub’

MS word, and windows, need to have

Arabic translation enabled, or they just put

the individual letters right to left.

see

http://office.microsoft.com/en-gb/word-help/install-system-support-for-multiple-languages-HP005258876.aspx?CTT=5 origin=HP003089535

1

( ); ) in French, a corruption of

(to ram or pound); Soil suitable for rammed earth is shown in Figure 1.5. If the rammed earth is not stabilised, then the soil mixture should contain more clay and

be stabilised, a silty, P e r c e n t a g e p a s s i n g 100 80 60 40 20 Clay 0.001  0.01 0.5

Particle size (mm) (logarithmic scale) Rammed earth Cob Adobe

Figure 1.5: Particle size distribution for different types

of earthen construction

To make a rammed earth wall, a formwork box is constructed to the width of the required wall. This box is filled with soil, which is then compacted by physical or mechanical means. Traditional formwork (Figures 1.6 and 1.7) can be moved along the length of the wall and vertically, so that when one formwork box is filled with earth, it can be dismantled and moved to allow further compaction to take place. Modern formwork (Figure 1.8) is similar to that used

(17)

Figure 1.7: Rammed earth wall under construction. Jomsom, Nepal

for concrete, and may be modular, allowing for large Modern rammed earth tends to use pneumatic or sections to be built in one go. electric hammers fitted with flat feet to provide

Soil is poured into the formwork, and usually compaction, whereas traditional rammers tend to compacted using a rammer in layers of around be timber poles with shaped ends, or sometimes 100 mm. The rammer may take a number of forms, incorporating stones at the end of the rammer. with a size and shape dependent on the culture. When the formwork box is filled, it is removed

(18)

7

and moved to another location, giving rise to characteristic ‘lifts’ in rammed earth construction. In some rammed earth traditions the formwork is supported on timbers placed on the wall, and these leave characteristic holes denoting the position of each lift (Figure 1.9)

Openings in rammed earth are formed using blanks, or by the placement of lintels between two rammed earth wall sections. Lintels may be curved (Figure 1.10), allowing feature openings to be

created. Traditionally, lintels were made from timber or stone, but modern rammed earth construction often features precast concrete or steel lintels.

TYPES OF EARTHEN CONSTRUCTION

Decoration of rammed earth can take the form of additional materials such as fired bricks between lifts (Figure 1.11), or the insertion of coloured layers of soil or relief patterns into a rammed earth wall.

Figure 1.10: Precast concrete lintel in modern rammed

earth. St Thomas More Church, Perth, Australia

Figure 1.9: Density banding, lifts between formwork

boxes, and holes through the wall. Villena, Spain

Figure 1.11: Rammed earth with decorative fired brick between the lifts. Villafeliche, Spain 1

(19)

1.3.2 Cob

Cob construction technique involves the direct placement of a mix of moist soil and straw to form a wall (Figure 1.12)[3]_{.The word} _cob _is

derived from the Old English word for loaf ,

and similar techniques are known by different names in different cultures, such as chineh (in

Farsi) and pakhsa (in Uzbek). A similar layered

techniquehas been described in Oman and Iran

(Figure 1.13)[4]_.

The particle size distribution of soil used for cob is shown in Figure 1.5. The soil tends to be more sandy than that used for adobe construction. Cob almost always contains short straw or grass added to the earth mixture to provide resistance to shrinkage cracking, and improved strength.

Cob is usually constructed by a team of two people, one working on the wall, and the other at the base, shovelling the cob mix to the head of the wall. A cob wall is constructed in layers 400–600 mm high; wet cob is forked into position and compacted at the head of the wall.

Figure 1.13: The layered technique (see wall, left).

Decorative adobes between each lift. Isfahan, Iran. Courtesy of Armin Yavari

(20)

9

Compaction takes place either by treading the mixture, or by using long-handled, flat-footed tampers[5]_{. Where the compacted cob falls outside}

the line of the wall, it may be shaved from the face to provide a vertical face. Construction progresses with each layer of cob allowed to dry slightly before the wall can be stood on and the next layer placed. Walls are typically between 0.5 m and 1 m thick, and may taper as the wall rises.

Openings are formed either by adding ‘blank formers’ to the wall, around which cob is placed, or by adding lintels at the correct height during construction and then cutting the openings out after the cob wall is finished.

Because of the free-form nature of cob, it is very simple to construct structures that curve both on plan and on elevation (Figure 1.14). For this reason, cob is often used as an artistic material for sculpture or temporary structures, and is very simply decorated either by inserting objects into the wall or by creating relief patterns.

TYPES OF EARTHEN CONSTRUCTION

1.4

UNIT CONSTRUCTION

1.4.1 Adobe

In contrast to in situ monolithic construction methods, many forms of earthen construction are based on units. Here the termunit is defined as a

block constructed from earth and allowed to air-dry before being used in the construction of a structure. (Fired bricks are manufactured using specific types

of clay, which are heated to high temperatures so that the clay is vitrified, and cinder,breeze or besser blocks are manufactured using cement, and

are quite different products.) Two types of unit construction are discussed here:adobe, used to

describe units that are constructed without recourse to mechanical advantage, and compressed earth blocks, constructed using a machine to provide increased compactive effort.

The termadobe has a range of meanings in

different cultures. Here it is used to describe a unit that may be formed by hand or in a frame, but which is not compacted. Units are made of similar

Figure 1.14: Modern cob building. Melon car park, Eden Project, UK. Courtesy of Jackie Abey and Jill Smallcombe,

Abey Smallcombe cob builders

(21)

kerpiç.

example into spheres or cuboids). More common is the use of a standardised mould; to increase productivity, moulds can be made to produce more than one brick at a time (Figures 1.15 and 1.16).

Figure 1.15: Adobe mould. Drâa Valley, Morocco

Figure 1.16: Adobes in moulds. Earth-building

course, UK

To make blocks, wet soil is placed into the mould and allowed to dry slightly; then the mould is removed and the unit is allowed to dry in the air (Figure 1.17). To assist drying, the bricks can be rotated onto their header face after a time, to allow a larger surface area to be exposed. The bricks are usually left to dry for a period of weeks before being laid to form a structure.

Figure 1.17: Adobes drying. Aït Ben Haddou, Morocco

This is the arabic for ‘al taub’

MS word, and windows, need to have

Arabic translation enabled, or they just put

the individual letters right to left.

see

http://office.microsoft.com/en-gb/word-help/install-system-support-for-multiple-languages-HP005258876.aspx?CTT=5 origin=HP003089535

size to each other to allow them to be laid together in a mortar to form a wall.

The term ‘adobe; is also likely to be taken from the Arabic for brick, al taub( ), where it has

been corrupted into the Spanishadobe. In Turkic

languages this type of construction is known as The soil used for adobe construction tends to be richer in clay and silt than the soil mixtures used for rammed earth or cob construction (Figure 1.5). These soil types may be more susceptible to

shrinkage, and so additives such as straw or grass are often included to prevent cracking.

Hand-formed units are made by roughly shaping the wet soil to the required dimensions. This method allows any shape to be formed (for

(22)

TYPES OF EARTHEN CONSTRUCTION 11

Adobe walls are constructed in the same manner as fired masonry, with similar bond patterns and mortar bed joints. The mortar should be composed of a similar material to that of the brick. To lay bricks, each brick is first dipped or coated in water, and then laid into the mortar bed. Adobe can be formed into arches (Figure 1.18), and barrel vaults and domes are popular in many parts of the world. Decorative patterns may be formed in adobe walls by using a different bond pattern, by laying the adobes on end, or by manufacturing insets or protrusions from the wall (Figure 1.19).Many adobe walls are rendered after construction. This both protects the face and allows a clean face to be presented, reducing the chance of water penetration into the mortar joints.

1.4.2 Compressed earth blocks

Compressed earth blocks (CEB) are made in a press, which allows a large compressive force to be imparted to the brick. This means that a lower water content can be used than for adobe (see Section 3.9), because a great compactive effort is applied, and thus a higher dry density brick is obtained. Moulds can be inserted to allow the brick to be faceted around the edges, and frogs and raised sections can be added to improve interlocking (Figure 1.20).

In some cultures, cement or other binders are added to the earth block mixture to improve the mechanical properties, and in these cases it is important to ensure that sufficient water is added to allow the full cementing reaction to take place.

A large amount of research has been undertaken by non-governmental organisations into the

improvement of earth brick presses for use in

developing countries. The CINVA ram was developed in the 1950s, and many agencies have contributed to the subsequent development of the presses, including the BREPAK machine[6, 7] _{and the Auram 3000 press}

developed and manufactured by the Auroville Earth Institute[8]_.

Cement-stabilised earth blocks must be allowed to cure for around 28 days before they are used in a structure. A mortar similar to that of the brick is used for their construction. Compressed earth blocks offer a viable alternative to fired brick or cement block construction (Figure 1.21). Buildings are usually painted or rendered using a cement-based render, and as a result do not appear any different from other construction types.

Figure 1.18: Adobe arches, Isfahan, Iran. Courtesy of

Armin Yavari

Figure 1.19: Decorative adobes. Aït Ben Haddou,

Morocco

Figure 1.20: Cement-stabilised compressed earth

blocks. Bangalore, India

(23)

Figure 1.21: Cement-stabilised compressed earth block

house. Bangalore, India

The type of construction is usually defined by the availability of suitable soils. Where clay and silty soils are found close to the surface, then adobe construction tends to dominate. Where more silty and sandy soils are found, rammed earth and cob construction are more common.

There is a wide variety within the techniques described. The dimensions and details of rammed earth formwork and rammers, the techniques for cob construction, and the shapes and sizes of adobe and compressed earth block differ greatly around the world.

The selection, grading and mixing of soils are requirements for all types of earthen construction. Mixing can take place using people or animals, or more mechanised means such as rotary mixers. Increased mechanisation has also led to improvements in compacted earthen construction, such as rammed earth and compressed earth block. In modern rammed earth construction, compaction using pneumatic or electric rammers is used rather than manual compaction, and compressed earth blocks use levers and mechanical advantage to impart compaction energy.

Chemical stabilisation has been practised for a very long time, either to improve the workability of the mixture, or to improve its mechanical properties. Historically, these chemicals have been bitumen or lime, but more recently cement has been added both to compressed earth blocks and to rammed earth, to produce what is perceived to be a more modern construction material. Physical stabilisation generally uses materials that are placed to act in tension within the earth, examples are materials such as straw, grasses or plastic fibres.

Earth building has recently been promoted as

1.5

CONCLUSIONS

a sustainable construction technique, because of This chapter has outlined earthen construction the low transport costs if materials are excavated techniques where earth is the main constituent. close to the construction site, and the low energy Distinct types of monolithic and unit construction input compared with more common construction have been identified, and the initial steps common techniques such as fired brick, Portland cement to all types of earth building have been described. or steel. The development, for example, of Independent of the construction type, earth cement-stabilised rammed earth and extruded structures are formed by shaping wet soil into the unfired clay bricks means that earthen building required shape, followed by some drying to form a may in the future take its place among more

(24)

2 HISTORY OF EARTH BUILDING 13

CHAPTER 2 HISTORY OF EARTH BUILDING

2.1

INTRODUCTION

Building using earth is one of the oldest construction techniques; it provides simple shelter using a freely available material. Buildings made from earth are found in many parts of the world, and in different forms, sometimes mixed with other traditional construction materials such as timber or stone, and sometimes with more modern inventions such as cement and steel. As described in Chapter 1, moist soil is formed either as a monolithic wall that is then allowed to dry, or into independent units, such as bricks or blocks, which are allowed to dry before being placed as a wall.

It is probable that earth-building techniques developed independently in different parts of the world, and spread with the movement of peoples. Early people were constantly moving, following hunting and gathering patterns dictated by the surroundings. The earliest shelters utilised natural

features such as caves, and the first earth buildings may have been extensions to natural features, such as mounds of earth at cave entrances or pits dug into the ground.

The development of settled agriculture allowed the first permanent shelters, because more time and effort could be expended in their construction. Agriculture first developed in fertile river valleys, and

here the silt and clays provided excellent building materials for earth construction. The first earthen building technique to develop is likely to have been wattle and daub: construction of a façade or roof using timber or grasses, which is then covered in earth. Later a rammed earth type of technique may have developed, with earth placed against or between walls made from timber and compacted into place, forming a thicker wall. The development of unit construction could have developed later; initially units were formed by hand, and later more cuboid blocks

(25)

were made using formwork. When dry, these could be transported, allowing the production of the materials to be separated from the location of the building, so that, for example, suitable earth could be taken from a river valley liable to flooding and used for the construction of buildings at a higher level.

Agriculture[9]_{and earth construction developed}

independently in the main cradles of civilisation. The development of agriculture beside major rivers led to people gathering together in towns for the first time. These fertile river valley civilisations had access to the right types of soil for earth construction, and there is evidence for the development of earth building independently in the valleys of the Tigris and Euphrates, Nile, Indus, Jordan, Murghab and Yellow Rivers. These cultures remained independent

from each other, yet appear to have developed very similar earth-building techniques. As civilisation and trade developed, techniques were refined and improved. This is difficult to chart, because earth-building techniques can vary from settlement to settlement and from year to year, but some patterns do emerge. It would appear that the transition from hand-moulded to cuboid bricks occurred in Mesopotamia around 5000BC, and that rammed earth was not found in South America prior to its introduction by Europeans.

Earth is generally used in combination with other building materials when these are available: for instance, wattle and daub houses combine earth construction with timber, and are found in Japan and northern Europe. Where stone is readily

available, earth is used as a plaster or a mortar, as in Malton in the north of England, or turf is used for roof or wall construction, as in the Western Isles of Scotland. There are also instances of monumental architecture in one construction type and vernacular construction in another, such as the stone cathedrals of England contrasting with the surrounding wattle and daub vernacular houses.

2.2

EASTERN ASIA

The Euphrates and Tigris river valleys were home to previously nomadic civilisations that first developed settled agriculture and buildings around 9000BC. These civilisations used hand-moulded oval bricks to form circular structures, found at sites of Djade

al-Mughara in Syria and Tappeh Ozbaki in Iran. These oval bricks appear to have been used until around 6000BC, at sites such as Jericho and Netiv Hagdud. From around 6000BC onwards, square bricks are found at the Tell Hassuna[10]_{site in Iraq, and at}

Jericho the buildings change from being circular on plan to rectangular.

Settlements along the Euphrates and Tigris rivers gradually grew in size and complexity. By 3500BC the city of Uruk was the largest in the region, with rammed earth buildings and adobe temples. Closer to the Arabian Gulf, the Assyrian cities of Ebla and Mari vied for influence, and excavations at these sites show that both sites had earthen city walls and adobe palaces[11]_.

Technology developed such that when the Ziggurat of Ur was constructed, around 2100BC, it was built with an adobe brick core and faced with fired brick set into bitumen[12]_{. Such ziggurats}

may have earlier been constructed in adobe, and have not withstood the ravages of time, or remain unidentified to the present day.

The settlement of Çatalhöyük developed independently on the alluvial plains of the

Çarşamba river in central Turkey. This settlement is still being excavated, but may have been the largest in the world at the time, with 5000 inhabitants at its peak between 7300BC and 6800BC[13]_{. The city was built from adobe, with}

irregular plan buildings packed so tightly that access was via the roofs.

Many settlements in this region feature a core of earthen buildings that have been renewed and rebuilt over the centuries. In Iran, the

cities of Yazd and Isfahan contain many historic adobe buildings (Figure 2.2). The city of Tous is surrounded by rammed earth walls, and the citadel of Bam, which dates from around the seventh century AD, was probably the largest adobe building in the world before its collapse in an earthquake in 2003[14]_{.In Yemen, the city of}

Shibam is renowned for its particularly tall adobe buildings. From around 1700, the residents began to build upwards, and currently around 500 adobe ‘skyscrapers’ reach up to 30 m high. Close by is the town of Tarim, home to the Al-Muhdhar Mosque. The adobe minaret of this mosque, completed in 1914, is probably the tallest earthen structure in the world, at 53 m.

(26)

HISTORY OF EARTH BUILDING 15

Figure 2.2: Cob and adobe walls at Ghaleh Yavar, a

castle outside Isfahan, Iran. Courtesy of Armin Yavari

2.3

�

CENTRAL ASIA AND THE INDUS

VALLEY

Settled civilisation developed in the Indus valley around 7000BC. The small adobe settlement of Mehrgarh in modern Pakistan was a forerunner of the much larger Indus valley civilisation that developed around 3000BC. The civilisation spread along the Indus river, with the two large settlements of Harappa and Mohenjo-daro emerging around 2600BC. Both settlements were laid out in a grid pattern, with adobe houses and individual streets.

Settled agriculture and the first buildings in central Asia are related to the Bactria-Margiana Archaeological Complex, comprising around

300 discrete fortified adobe brick enclosures at sites such as Namazga-, Altyn- and Gonur-Depe that have been dated to between 2200BC and 1700BC. Although the peoples of central Asia were largely nomadic, in western Uzbekistan

there are several forts orqalasbuilt in adobe, and

these are thought to date from around 300BC. Few of these settlements have remained to the present day because of shifting trading patterns, conflict, and meandering rivers. Settlements that did survive grew to become major trading centres such as Balkh and Merv.

Balkh (Bactria) in modern Afghanistan is called

Umm Al-Belaad(Mother of Cities) because of its

antiquity. Although the city dates from 2000BC, the oldest standing structures are the rammed earth Takht-e Rostamand Top-Rustam dated AD 300–500 and attributed to the Buddhist or Zoroastrian

religions. Balkh became a pre-eminent city in the region, and a centre of trade and commerce[15]_.

When Muslim traveller Ibn Hawqal visited the city around AD 950 he described it as ‘built of clay with ramparts and six gates’.

The city of Merv in Turkmenistan is relatively unique among archaeological sites, with several different settlements constructed adjacent to rather than on top of each other, allowing archaeologists to uncover earlier structures without destruction of those built later. Almost all of the structures in Merv are built in earth, with the earliest settlements dated to around 2000BC. The city was almost continually inhabited until its abandonment and destruction in 1787, and is now a major archaeological site[16]_.

Both Merv and Balkh lay on important trade routes that crossed central Asia, and many other earthen settlements grew up on what has become known as the Silk Road. The adobe city of Panjakent in western Tajikistan is first mentioned around 500BC, and was probably the highlight of the Silk Road before its decline in the eighth century[17]_{.The site has been extensively}

excavated since the 1940s, and is now a tourist attraction. Further east, the Uyghur empire capital and Silk Road city of Ordu-Baliq (Khar Balgas) in modern Mongolia featured rammed earth defensive walls and buildings. The city was established in AD 745, but was abandoned in AD 840. The armies of Alexander the Great around 330BC, the Muslims around AD 720, and Genghis Khan in 1220 each ransacked or destroyed many earthen settlements, and as a result many of the sites in central Asia are mere shadows of their former selves.

(27)

2.4

ASIA

Settled civilisation in China first developed around 2300BC when nomadic peoples settled on the alluvial plains of the Yellow River, beginning with the Lungshan civilisation. The soft soils here could be cut to form pit houses and heaped to form rammed earth mound walls. This allowed the development of defensive settlements such as those found at Lianyungang, Jiangsu, Taosi, Erlitou and Longwan[18]_.

Evidence of formwork boards and ramming

implements have also been found at Pingliantai[19]_.

During the Warring States Period (475–221BC) rammed earth was used for the construction of more elaborate walls at larger settlements such as Langya, Anyang, Linzi and Xiadu. The Qin dynasty (221–206BC) was the first to construct rammed earth defensive walls along their northern frontiers in western China. These walls were repaired and extended by the Han (206BC–AD 202) and Jin (AD 265–420) dynasties. The Tang dynasty (AD 618–907) expanded Chinese borders and trade, but was harassed by tribes to the north, and as a result built fortified settlements in north-western China along the eastern part of the Silk Road. These settlements, such as Jiaohe, Gaochang and Xi’an, are all encircled with large rammed earth walls, and the city of Kashgar in western China is built from adobe, whereas the fortress of Baishui, at the western end of the Great Wall, is constructed wholly in rammed earth[20]_.

The Tang dynasty collapsed around AD 907, which led to a period of major upheaval in China. The next dynasty to produce major monumental earth architecture was the Ming dynasty (1368– 1644), which pursued a policy of aggressive expansion. The walls of the Ming capital Xi’an, originally of rammed earth, were faced in stone, and along the Silk Road and to the northern borders the Great Wall was repaired and upgraded, and new forts were constructed in adobe at Jiayuguan (Figure 2.3) and Hexibao.

In the Fuijan province of central China, the round houses of the Hakka people have recently been given World Heritage site status. These large rammed earth buildings, calledTulou(literally ‘earth structures’) are

defensive homes to many families, and can be up to 60 m across and four storeys tall. The oldest of these buildings was built in 1308, and their construction continued well into the 20th century.

Figure 2.3: Part of the early Ming dynasty Great Wall,

Jiayuguan Fort, China. Courtesy of Kate Clarke

There are interesting parallels between the Chinese characters and the ideas they represent. The character for rammed earth hāngtŭ( )

is composed of the word shăng ( ), meaning

‘to ram’, and tŭ( ), meaning ‘earth’. The word shăng is itself made up of the radicals dà ( ),

meaning ‘big’, and lì ( ), meaning ‘strength’, thus

imparting the idea that rammed earth walls are big and strong. Earth ( ) is also a character in the words for city walls, chéng ( ), and internal walls, qiăng ( ), indicating that earth was used for wall

construction.

Rammed earth and adobe are found on the Tibetan plateau and in parts of the Himalayas as both monumental and vernacular building techniques. At the west end of the Himalayas rammed earth is found in the north Indian state of Ladakh, in palaces such as those at Shey and Leh (Figure 2.4), and in a fort at Basgo. In the Nepali kingdom of Mustang, much of the capital city of Lo Manthang is constructed from rammed earth, and a defensive wall, dating from 1380, surrounds

(28)

Figure 2.4: Leh Palace, Ladakh, India

the city[20]_{. The country of Bhutan, at the east}

end of the Himalayas, continues to promote traditional building materials, with many homes and monumental architecture built in rammed earth (Figure 2.5).

Figure 2.5: Rammed earth section of private house near

Kyichu Lhakhang monastery, Bhutan

2.5

AFRICA

Although Africa is known as the cradle of mankind, archaeology has not yet revealed a great history of earth building in Africa. The African mud hut, constructed from woven reeds or timber with an earth plaster, may have remained unchanged for millennia[21]_{. The earliest woven reed and branch}

earth-covered sites have been dated to 5000BC at sites in the Nile Delta, such as Mermide and Fayum. The Egyptian dynasties appeared in the Nile valley around 2900BC, and the clay river silt mixed with desert sand and straw from cultivated grains allowed hand-made adobe brick manufacture. The large independent adobe structures at Shunetel-Zebib and Nekhen, dating to 2750BC, and adobe pyramids found at Tanis[22]_{show that adobe was}

used as a monumental construction technique before the better-known stone edifices were built.

Adobe continued to be used as a vernacular construction material in Egypt. The settlement of Deir el Medina (1550–1080BC), which was home to the masons of the Valley of the Kings, comprises square, single-room adobe houses laid out in a grid pattern. A relief and frescoes at the tombs of Queen Hatshepsut (d. 1458BC) and an official during her reign, Rekhmire, both describe the process for making rectangular adobe bricks in formwork. The city of Tel el-Amarna was a new capital city built by the pharaoh Akhenaten around 1353BC but abandoned soon afterwards. This city features single-storey rectangular adobe buildings with external stairs leading to a flat roof.

Rameses II (1279–1213BC) embarked on many building projects, and adobe bricks from his major construction projects were stamped with his seal[23]_.

Egypt, however, remained relatively isolated from the rest of Africa, and as a result had little influence on the building techniques found throughout the rest of the continent.

In north Africa, the Phoenician civilisation spread from the eastern Mediterranean, founding settlements along the north coast. Their capital at Carthage (in modern Tunisia) was founded in 814BC, and excavation reveals rammed earth walls used in homes there[18]_{. The famous Carthaginian}

general Hannibal crossed into Europe in 218BC, and the Roman author Pliny the Elder describes the rammed earth towers in Africa attributed to Hannibal[24]_.

(29)

“Moreover

“Moreover, are there , are there not in Anot in Africa and Spainfrica and Spain

walls made of earth that are called framed walls,

because they are made by packing a

because they are made by packing a frameframe

enclosed between two boards, one on each side,

and so are stuffed rather than built, and do they

not last for ages,

not last for ages, undamaged by rain, wind andundamaged by rain, wind and

fire, and stronger than quarry stone? Spain still

sees the watchtowers of Hannibal an

sees the watchtowers of Hannibal and turrets ofd turrets of

earth placed on mountain ridges.”

Around AD 700 Islam spread through north Around AD 700 Islam spread through north Africa, and the valleys of the Drâa and Dadès rivers Africa, and the valleys of the Drâa and Dadès rivers

in modern Morocco are filled with hundreds of in modern Morocco are filled with hundreds of rammed earth kasbahs (Figure 2.6), such as Aït rammed earth kasbahs (Figure 2.6), such as Aït Ben Haddou and Tamnougalt, the earliest dated to Ben Haddou and Tamnougalt, the earliest dated to around AD 1000. The city walls of both Marrakech around AD 1000. The city walls of both Marrakech and Fes are built in rammed earth, and it appears and Fes are built in rammed earth, and it appears extensively in monumental Muslim architecture, extensively in monumental Muslim architecture, such as at the El Badi Palace in Marrakech, built in such as at the El Badi Palace in Marrakech, built in 1578. Muslim rule in Egypt promoted the use of 1578. Muslim rule in Egypt promoted the use of adobe brick, with the 10th-century Fatimid tombs adobe brick, with the 10th-century Fatimid tombs built in adobe

built in adobe[25][25]_..

Moses Maimonides, a Jewish writer and Moses Maimonides, a Jewish writer and

philosopher, born in Cordoba in 1135, but residing philosopher, born in Cordoba in 1135, but residing in Morocco, Egypt and Israel, wrote of rammed in Morocco, Egypt and Israel, wrote of rammed earth

earth[16][16]_::

“The builders take two boards, about six

cubits long and two cubits high, and

cubits long and two cubits high, and place themplace them

parallel to each other on thei

parallel to each other on their edges, as far apartr edges, as far apart

as the thickness of the wall they wish to build;

they steady these boards with pieces of

they steady these boards with pieces of woodwood

fastened with cords. The space between the

boards is then filled with earth, which is beaten

down firmly with hammers or stampers; this is

continued until the wall reaches the requisite

height and the boards

height and the boards are withdrawn.”are withdrawn.”

Although complex societies have been present Although complex societies have been present in west Africa since around 1500BC, the first

in west Africa since around 1500BC, the first

documented is the Ghanaian empire, ruling a large documented is the Ghanaian empire, ruling a large part of west Africa from around AD 830. While part of west Africa from around AD 830. While much of the monumental architecture is stone, it much of the monumental architecture is stone, it is assumed that current earth-building practices is assumed that current earth-building practices found in Ghana (Figure 2.7), such as adobe and cob found in Ghana (Figure 2.7), such as adobe and cob

Figure 2.6:

(30)

HISTORY

HISTORY OF EARTH OF EARTH BUILDINGBUILDING 1919

Figure 2.7:

Figure 2.7: Vernacular mud brick at Yikpabongo Vernacular mud brick at Yikpabongo village,village,

Ghana. Courtesy of Claire Jaquin

Figure 2.8:

Figure 2.8: Great Mosque of Djenné, Great Mosque of Djenné, Mali. Courtesy ofMali. Courtesy of

Carolina Castellanos

construction, were used in vernacular architecture construction, were used in vernacular architecture in antiquity. The demise of the Ghanaian empire in antiquity. The demise of the Ghanaian empire around 1235 precipitated the development of around 1235 precipitated the development of the Mali Empire, with its famous earthen cities of the Mali Empire, with its famous earthen cities of Djenné and Timbuktu.

Djenné and Timbuktu.

The original great mosque of Djenné was The original great mosque of Djenné was probably first built around 1200, but fell into probably first built around 1200, but fell into disrepair before being reconstructed in 1907 disrepair before being reconstructed in 1907[26][26]_..

The characteristic style is similar to other sites in The characteristic style is similar to other sites in west Africa, such as the Sankore and

west Africa, such as the Sankore and DijinguereDijinguere Ber mosques in Timbuktu in Mali, built around Ber mosques in Timbuktu in Mali, built around 1320, and the Grand Mosque of Agadez in Niger, 1320, and the Grand Mosque of Agadez in Niger, built around 1515. These buildings are unique, built around 1515. These buildings are unique, being decorated with bundles of palm

being decorated with bundles of palm stalks thatstalks that project from the wall and serve as a

project from the wall and serve as a scaffold forscaffold for annual replastering of the buildings (Figures 2.8 annual replastering of the buildings (Figures 2.8 and 2.9)

and 2.9)[27][27]_..

Earth buildings are found as far east as Earth buildings are found as far east as Cameroon, where the homes of the

Cameroon, where the homes of the MusgumMusgum people are inverted catenary

people are inverted catenary dome structuresdome structures built in earth

built in earth[28][28]_{. Monumental earth buildings}_{. Monumental earth buildings}

are not found in the forested and

are not found in the forested and more humidmore humid regions of central and southern Africa, but earth regions of central and southern Africa, but earth construction in various forms continues to be construction in various forms continues to be used across Africa.

used across Africa.

Figure 2.9:

Figure 2.9: Dijinguere Ber Mosque, Timbuktu, Mali. Dijinguere Ber Mosque, Timbuktu, Mali.

Courtesy of Carolina Castellanos

2 2

(31)

2.6

EUROPE

Earth building takes many forms in Europe, with Earth building takes many forms in Europe, with adobe and rammed earth found in southern adobe and rammed earth found in southern Europe, whereas in northern Europe earth is used Europe, whereas in northern Europe earth is used in conjunction with timber in wattle and daub in conjunction with timber in wattle and daub and half-timbered techniques. The earliest use of and half-timbered techniques. The earliest use of adobe in Europe can be dated to around 5300BC adobe in Europe can be dated to around 5300BC at the settlement of Sesklo in Greece, with small at the settlement of Sesklo in Greece, with small homes built on stone foundations

homes built on stone foundations[29][29]_{. The use of}_{. The use of}

earth with timber in northern Europe means that earth with timber in northern Europe means that many archaeological sites have decayed, and only many archaeological sites have decayed, and only foundations remain, making it difficult to assess the foundations remain, making it difficult to assess the building materials. Further east, in Hattuša, central building materials. Further east, in Hattuša, central TTurkeyurkey, remains , remains of adobe of adobe buildings dated to buildings dated to aroundaround 1600BC have been found.

1600BC have been found.

Rammed earth may have been brought to Rammed earth may have been brought to Europe by the Phoenicians, who spread from the Europe by the Phoenicians, who spread from the eastern Mediterranean and founded settlements in eastern Mediterranean and founded settlements in Spain, such as Morro de Mesquita

Spain, such as Morro de Mesquita[18][18]_{. The Roman}_{. The Roman}

architect Vitruvius describes rammed earth used architect Vitruvius describes rammed earth used in the French city of Marseille, and adobe being in the French city of Marseille, and adobe being used to construct the Greek city of Athens used to construct the Greek city of Athens[30][30]_..

The Latin verb

The Latin verb pinsere pinsere, meaning ‘to pound’, has, meaning ‘to pound’, has

passed into French as

passed into French as pisé pisé, meaning rammed earth., meaning rammed earth.

Although much Greek and Roman monumental Although much Greek and Roman monumental

architecture was built in stone, earthen construction architecture was built in stone, earthen construction

continued to be used in vernacular construction continued to be used in vernacular construction throughout Europe. St Isidore, the Catholic bishop throughout Europe. St Isidore, the Catholic bishop of Seville, described the rammed earth technique, of Seville, described the rammed earth technique, paraphrasing Pliny in his work

paraphrasing Pliny in his work EtymologiaeEtymologiae, written, written

before AD 636 before AD 636[31][31]_..

Islam came to southern Europe in AD 711, Islam came to southern Europe in AD 711, bringing with it building technologies from north bringing with it building technologies from north Africa. Conflict at this time led to the construction Africa. Conflict at this time led to the construction

of many rammed earth and adobe fortifications. of many rammed earth and adobe fortifications. Excavations of the fortifications of Calatayud in Excavations of the fortifications of Calatayud in Spain have been dated to AD 884, and the Muslim Spain have been dated to AD 884, and the Muslim defensive walls of historic cities of Cordoba, Seville defensive walls of historic cities of Cordoba, Seville and Granada are built in rammed earth. The World and Granada are built in rammed earth. The World Heritage site of the Alhambra Palace in Granada Heritage site of the Alhambra Palace in Granada (Figure 2.10) was constructed from rammed earth (Figure 2.10) was constructed from rammed earth around 1238.

around 1238.

Though earth continued to be used as a Though earth continued to be used as a building material, its use declined with the building material, its use declined with the increasing penetration of fired brick from the increasing penetration of fired brick from the 16th century onwards. In northern Europe, wattle 16th century onwards. In northern Europe, wattle and daub techniques developed as

and daub techniques developed as vernacularvernacular structures. Cob structures dated to around 1400 structures. Cob structures dated to around 1400 have been found in parts of the UK

have been found in parts of the UK [32][32]_{, and this}_{, and this}

building technique continued to be used as a building technique continued to be used as a vernacular technique until well into the 19th vernacular technique until well into the 19th century.

century.

Figure 2.10:

(32)

At the end of the 18th century the political climate in Europe was turning towards freedom for the common man and revolution against the ruling classes. In this climate, rammed earth was ‘rediscovered’ and championed by Frenchman François Cointeraux. Cointeraux published a series of leaflets on rammed earth in Lyon in 1791[33]_.

These were translated into English[34, 35]_{, German}[36]

and Italian[37]_{, allowing the technique to spread}

across Europe (Figure 2.11) and to the United States[38]_.

Earth building again declined with the advent of the Industrial Revolution in Europe, because fired brick became more easily available, but was again rediscovered following the world wars. After the First World War, trials of rammed earth and rammed chalk buildings were undertaken in the UK [39]_,

championed by architect Clough Williams-Ellis[40]_,

and following the Second World War rammed earth was used in East Germany, leading to the development of the first German building standard for the material.

Earth building in Europe is now seeing a

revival, with national associations in many European countries. Traditional earth building conservation has been studied, and best practice guides have

Figure 2.11:Haus Rath, Weilburg, Germany.

Constructed 1828

been produced[41, 42]_{. The number of modern}

earth buildings is increasing, led by specialist earth-building practitioners such as Martin Rauch and Gernot Minke. Research and development into earth building is being undertaken by research groups at CRA Terre in France, and at several institutions in the UK, including the universities of Durham and Bath.

2.7

NORTH AMERICA

Earth was used as a construction material by Native Americans in modern Mexico and the southern

United States. The Aztec civilisation in Mexico constructed major monumental architecture in cut stone, but vernacular buildings are thought to have been adobe. The Hohokam culture of southern Arizona constructed adobe homes with slightly sunken floors cut into the alluvial soils, and remains of adobe Hohokam structures at the Casa Grande National Monument have been dated to around AD 600[43]_{. The Pueblo peoples of modern}

New Mexico built adobe structures several storeys high that were home to numerous families. The most famous is the Taos Pueblo, which is dated to around AD 1000[44]_.

Europeans coming to North America continued to use adobe for the construction of many missions and frontier forts, such as the adobe Tamacacori, Guevavi and Calabazas Jesuit missions in Arizona built in 1691. In Albuquerque, the governor’s house was built in adobe in 1706. As European settlement moved westwards, forts were established to protect the settlers from Native American raids. Remains of the adobe Fort Union (1851) and Fort Selden (1865) are testament to the US army using the available materials to construct defences.

Many cities on the west coast, such as San Jose and Los Angeles, may have originally been

constructed in adobe, but continual expansion and rebuilding mean that little remains of these original structures. A single adobe wall remains in Santa Clara University in San Jose, built in 1822 and part of the original lodges around which the university was founded. Casa de Estudillo in the Old Town of San Diego was built using adobe in 1829, and has recently been restored as a historic monument. Lured by gold mining, Chinese immigration to

(33)

Figure 2.12: Church of the Holy Cross, Stateburg, South

Carolina, USA. Courtesy of David Grey

the west coast of the United States brought with it construction techniques such as rammed earth, which was previously unknown in the region. In Palo Alto, California, a businesswoman named Juana Briones built a rammed earth and cob

house in 1845, and Chinese immigrants built a rammed earth herb shop in 1855 (the Chew Kee Store in Fiddletown, California[45]_{). Later}

European immigrants are probably responsible for roughly 150 rammed earth buildings clustered in the San Antonio Valley in Monterey County, built around 1896[46]_.

German immigrants to the east coast of the United States brought the rammed earth technique from Europe. Hilltop House in Washington, DC, was built in 1773 in rammed earth. Bushrod Washington (nephew of George Washington) built rammed earth lodges on his estate at Mount Vernon in Alexandria, Virginia, in 1812. Future US president and architect Thomas Jefferson was aware of the technique[38]_{, but it is unlikely that he}

personally constructed any buildings in rammed earth, although slave quarters at the Bremo

Plantation in Virginia, designed by Jefferson, were built in this material by his friend General John Hartwell Cocke around 1819.

A rammed earth house was built in Trenton, New Jersey, by S W Johnson, drawing on the work of François Cointeraux in Europe. Johnson hoped to provide a model to newly arrived Europeans to settle farm land, and published a pamphlet in 1806 detailing rammed earth construction[35]_{. This}

new construction technique was championed by John Stuart Skinner, editor ofThe American Farmer

magazine, who published many articles on rammed earth in the early 19th century. Others began to experiment in rammed earth, and there are many articles in periodicals from the time referring to rammed earth. South Carolina academic William Anderson was a key proponent of rammed earth,

and in 1850 built the Church of the Holy Cross near Stateburg, South Carolina (Figure 2.12).

Experimentation with new building techniques in New Orleans led to the construction of the new Marine hospital in 1867[47]_{. This building was to}

be iron framed, with rammed earth infill panels. Construction began, but the building was vastly over budget, never completed, and eventually demolished. The use of rammed earth extended