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Building with Earth

Page 99

enced by their coatings. Table 12.2 gives

some capillary water intake coefficients

(w-values) of loam plaster with and without

a variety of treatments:

Making surfaces water-repellent

Water repellents
Several colourless liquids can be used to

impregnate loam surfaces, making them

water-repellent. A given impregnated sur-

face is considered water-repellent if the

wetting angle of contact made by a drop of

water is greater than 90° (12.3). The water-

repelling agent penetrates into the pores of

the loam without closing them, so that

while capillary water intake is significantly

reduced, vapour diffusion is not. As a rule,

these substances are dissolved in organic

alcohols, hydrocarbons or water.

The following groups of repellents can be


– silane and siloxanes

– polysiloxanes (silicone resins)

– siliconates

– acrylic resins

– silicate ester with hydrophobising addi-


– silicates with hydrophobising additives.

Silane, siloxanes and silicone resins react

chemically with mineral substances in the

loam and are highly weather-resistant; they

reduce water intake by more than 90%.

Vapour diffusion is decreased by only 5%

to 8%.

Silicate ester and acrylic resins show similarly

promising water-repelling effects, but they

reduce vapour diffusion by 15% to 30%.

Since the water repellents found on the

market have different compositions and

varying effects, they should be tested before

use. The water absorption coefficient w of

different loam plasters which were flooded

twice with different water repellents lies

between 0.0 and 0.2 kg/m2h0.5 (see 12.2).

Application of water repellents
With the so-called ”flooding“ technique,

water repellents are applied at least twice,

with the solution applied with rollers, so that

the liquid oozes and runs off as the roller is

pulled down over the surface. The second

flooding has to be done before the first is

dry. The loam surface has to be dry, and

neither cooler than 8°C nor warmer than

25°C before being treated. Only silanes and

siloxanes require the ground to be some-

what moist. Normally, this application has to

be repeated every few years owing to the

deteriorating effect of weather on these


A simple method of checking the amount

of water repulsion, used by the BRL, is

shown in 12.4. Here, the treated test sam-

ples are rotated at the rate of 7.5 rotations/

min on a base and passed under a shower

where water at 36°C is sprayed at a rate

of 12 litres per minute through an ordinary

hand shower. Another more sophisticated

apparatus was described in chapter 2, p. 26.

Lime plasters

Loam plasters used on exterior walls

(described in chapter 11) are only suitable if

they are without cracks and water-resistant.

As a rule, exposed surfaces should not have

loam plasters, the most common alternative

being lime plaster. Cement plasters are not

appropriate, as they are too brittle. They

cannot withstand strong thermic and hygric

forces without cracking, allowing water to

penetrate the loam to cause swelling, which

Weather protection101


12.2 w-values of loam
plasters with coatings
12.3 Drop of water
on a surface that has
been treated with
water repellent (right,
angle larger than 90°)
and on an untreated
surface (left, angle
smaller than 90°)
12.4 Simple spraying
test (BRL)
12.5 Church of San
Francisco de Asis,
Ranchos de Taos, USA


Page 100

in turn enlarges cracks and even causes

plaster to flake off.

During repairs undertaken in 1992, the old-

est German rammed earth house, built in

1795 (1.10), was found to have massive frost

erosion, which had destroyed the loam up

to a depth of 20 cm, because water had

penetrated through cement plaster applied

some decades before. A similar phenome-

non was reported from New Mexico, USA

by Bourgeois (1991). During a restoration

carried out in 1967, the church in Ranchos

de Taos (12.5), constructed of adobes in

1815, was covered with cement plaster.

Eleven years later, the cement plaster had

to be dismantled when the loam below

showed heavy moisture damage.

In cold climates, quick drying of the wall is

necessary if rain penetrates from the outside

or if vapour condensation from the inside

occurs. Therefore, the vapour diffusion

resistance of the outer layer should be

lower than that of the inside.

The German standard DIN 18550 (Part 3)

states that water-repellent external plasters

should fulfil the following conditions: water

absorption coefficient w � 0.5 kg/m2 · h0.5,

the specific vapour diffusion resistance sd
must be � 2.0 m and the product w · sd �

0.2 kg/m · h0.5.

The following sections describe the compo-

sition and application of non-loam contain-

ing plasters.

Preparation of ground
To provide a good bond, loam surfaces

that are to be plastered should be dry and

rough. Smooth surfaces should be sprayed

with water, so that their outer layers will

moisten and swell, after which they can be

grooved diagonally 2 to 3 mm deep, as

shown in 11.2. While the surface so pre-

pared is still moist, it should be primed with

thin lime milk, which should penetrate the

ground up to a depth of several millimetres.

A mix of 0.5 to 1 part of fat-free white

cheese, 2 parts hydraulic lime and 30 parts

water has also proved successful. If the lime

plaster is exposed to severe thermal forces,

if the unbroken area of the plaster surface is

very large, or if the bond is poor, expanded

metal meshes or reed mats fixed to the

ground may be required to take the plaster.

When using reed mats, it is advisable to dip

them in lime milk to prevent rotting.

Larger unbroken panels subject to strong

thermal forces may require reinforcement.

For this purpose, a galvanised steel net with

hexagonal meshes (rabbit or chicken wire

mesh) or similar nets are commonly used.

Workmen often prefer using plastic covered

glass-fibre nets because they do not cor-

rode and are more pliable.

Normal lime plaster usually consists of

1 part hydraulic lime and 3 to 4 parts sand.

Since it is commonly used in construction

worldwide, it is not discussed further in this

book. However, lime-casein plasters are less

common, and are therefore described


Old recipes often prescribe that animal hair

and casein be added to a normal plaster

to improve its behaviour. In former times,

casein was added in the form of whey or

buttermilk. Casein and lime react chemically

to form calcium albuminate, a wash-resist-

ant compound. The addition of casein

reduces the water absorption of lime plas-

ter, but at the same time hinders vapour


At the BRL, a lime-casein plaster for exterior

work was successfully tested. The mix con-

sisted of fat-free cheese, hydraulic lime and

sand in a ratio of 1:10:40. The lime has to

be first intensively mixed into the cheese to

form a creamy paste without adding any

water. After allowing the mix to rest for a

while, water and sand should be added.

For a thinner plaster that can be brushed on,

a slightly different mixture might be ade-

quate, with the proportion 1:6:25 of the

same ingredients respectively. In warm cli-

mates, some kitchen salt should be added

to keep the lime plaster moist for a longer

period, which improves curing.

Weather protection102

12.6 µ-values of
lime plasters (figures
referred to as volu-
metric parts)
12.7 Loam wall with
additional exterior
insulation and wood-
en planks forming air
12.8 Plinth designs
made incorrectly and


Page 197

Turowski, R.: Entlastung der Rohstoff- und
Primärenergiebilanz � Dissertation, University
of Essen, Germany 1977.

United Nations Centre for Human Settlements
(ed.): Earth Construction Technology. Nairobi,
Kenia 1992.

Volhard, F.: Leichtlehmbau. Karlsruhe, Germany

Vorhauer, K.: Low Cost/Self Help Housing. Gate
Modul 6/6. Eschborn, Germany 1979.

Voth, B.: Boden, Baugrund und Baustoff. Wies-
baden/Berlin, Germany 1978.

Walker, P.; Keable, R.; Martin, J.; Maniatidis, V.:
Rammed earth: design and construction
guidelines. BREPress, Bracknell, Great Britain

Wehle, K.: Werkstoffe und Techniken der Malerei.
Ravensburg, Germany (5th edition) 1985.

Weiss, A.: Angewandte Chemie 75 (1963),
pp. 755-762.

Weller, K.; Rehberg, S.: Lösungsansätze für den
energie- und rohstoffsparenden Wohnungs-
bau. DFG research project, Technical University
of Berlin, Germany 1979.

Yazdani, H.: Erhöhung der Lebensdauer von
Lehmbauten in erdbebengefährdeten
Gebieten Afghanistans. Dissertation, University
of Kassel, Germany 1985.

Zogler, O.: Wohnhäuser aus Lehm. Munich,
Germany 2004.


The author wishes to thank all students, assistants
and colleagues, who have contributed to the
research and development projects in Germany,
Argentina, Bolivia, Brazil, Chile, Guatemala,
Ecuador, Hungary, India, Nigeria and Russia. It is
owing to these efforts that this book contains
so much data and accounts of practical work
Special thanks are due to the research assistants
H. G. Merz, Ulrich Merz, Klaus Eckart, Ulla Lustig-
Rössler, Kiran Mukerji, Ulrich Boemans, Uwe
Jaensch, Dittmar Hecken, Alexander Fischer,
Arno Reich-Siggemann, Friedemann Mahlke,
Marcio Rosa d’Avila, Ernst Müller, Saskia Baden and
the technician Frank Millies, who built most
of the newly developed test apparatuses and
construction devices.

The author also wishes to thank Pawan Kumar
and Anke Lubenow, who helped in making the
drawings; Ulrich Boemans, Sigrid Köster, Uwe
Jaensch and Friedemann Mahlke, who prepared
the computer graphics; Gabrielle Pfaff, who
designed the layout; as well as Shalini Hingorani,
Rajeshwari Prakash, Sanjay Prakash and Ian Pepper
for their assistance with the translation. Last but
not least, the author expresses his gratitude to
Ria Stein and Michael Wachholz, who provided
editorial assistance and conducted image research.

Kassel, February 2006
Gernot Minke

Illustration credits

Adle, Kamran (Aga Kahn Award for Architecture):
p. 175 top and bottom

Atlas-Copco: 5.11
Anderson, Ken: p. 166
Bochow, K.-H.: 6.3
Breshna: 14.30
Bucaretchi, Maxim: p. 172 left and right; p. 173

top and bottom
CEPED: 5.26
Consolid: 6.14
Dressler, F.: 8.8
Dufter, S.: 7.1, 7.2
El Badwan, G.: 14.29
Enchantment Resort (Mii Amo): p. 187 top
Fischer, Alexander: p. 160 top and centre
Gerster-Rapho: 1.6
Glauser, Philippe: p. 174 top
Gnädinger, Alexander: cover
Gruner, D.: 1.4
Heuser: 5.12
Huber, Samuel: 192 top
Karcher, Joaquin: p. 162 top, centre right and left,

p. 163; p. 164 top, centre right and left; p. 165
Klomfar, Bruno: 192 bottom, 193
Lauber, Wolfgang: 1.9
Lorenz-Ladener, C.: 6.4
Lukas, G.: 8.9, 8.10
Mein, Trevor: p. 168 top, centre right and left;

p. 169 top and bottom
North, Graeme: p. 170 top and centre left; p. 171
Nothelfer, Michael: p. 158 top, p. 159 top, bottom

right and left
OKOKOK Productions: p. 157 top, bottom right

and left
Oliver, D.: 5.22, 5.23
Pacific Adobe: 6.15
Payne, Alan and Trish: p. 188 top, centre right

and left, bottom
Predock, Jason: p. 194 top; p. 195
Reynolds, M.: 14.4
Schijns, W.: 14.25
Sohie, Caroline: p. 184 left and right; p. 185 top

and bottom right
Süß, Andreas: p. 190 top; p. 191 top and bottom
Trappel, Ray: p. 167 top and bottom
Weller, K.: 6.16, 6.17
Wolf, S.: 5.27, 5.28
Wright, Anthony: p. 189 top and bottom
Yazdani, S.: 1.5, 14.54, 14.55
Zernike, Harry: p. 186 top and bottom, p. 187

bottom right

All other images: Minke, Gernot


Page 198


Graphic design: Gabrielle Pfaff, Berlin
Translation: Shalima Hingorami, Rajeshwari
Prakash, Sanjay Prakash, New Dehli, India;
Ian Pepper, Berlin, and Gernot Minke, Kassel,

A CIP catalogue record for this book is available
from the Library of Congress, Washington D.C.,

Bibliographic information published by
Die Deutsche Bibliothek
Die Deutsche Bibliothek lists this publication in the
Deutsche Nationalbibliografie; detailed biblio-
graphic data is available in the internet at

This work is subject to copyright. All rights are
reserved, whether the whole or part of the mate-
rial is concerned, specifically the rights of transla-
tion, reprinting, re-use of illustrations, recitation,
broadcasting, reproduction on microfilms or in
other ways, and storage in data banks. For any
kind of use, permission of the copyright owner
must be obtained.

' 2006 Birkhäuser � Publishers for Architecture,
P.O. Box 133, CH-4010 Basel, Switzerland
Part of Springer Science+Business Media
Printed on acid-free paper produced
from chlorine-free pulp. TCF �

Printed in Germany
ISBN-13: 978-3-7643-7477-8
ISBN-10: 3-7643-7477-2

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Front cover: Chapel of Reconciliation, Berlin,

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