Building with Earth: Design and Technology of a Sustainable Architecture

6 kg of tallow (melted suet) is poured into
36 litres of water. This mixture is stirred care-
fully (care has to be taken because the lime
reacts very intensely with water and may
splash and burn the skin). After adding 6 kg
of kitchen salt and carefully stirring, this mix
should be allowed to stand for 24 hours in
a not-too-cold environment. The water layer
that forms on the top of the mixture is
decanted. The pasty mix that remains is
then mixed with 3 kg of fine quartz sand
and applied with a brush in 3 to 5-mm-thick
layers to the wall (Manandhar, 1983). This
coating requires several weeks to cure. In
Nepal, it is said to last for four to six years.
A similar recipe was used successfully in
Australia (Department of Housing, 1981).
Tests performed with this mix at the Build-
ing Research Laboratory (BRL) showed that
it bonds well with a rough, lean loam plas-
ter. But with a rammed earth surface made
of clayey loam, parts of the coating became
detached over a period of several months
due to rain and frost, probably because the
bond between the coating and the ground
was insufficient.

Other stabilised lime washes
Several old text sources claim that in addi-
tion to mixing hydraulic lime into whey, it
can also be mixed into urine. Weiss (1963)
found that using Kaolinite clay, strength
could be increased by adding urea and
ammonium acetate. This practice was also
common in ancient China, where extremely
thin porcelain was produced by adding
putrefying urine to the mix.
According to Jain et al. (1978), the addition
of 70 g of animal glue dissolved in 0.5 litre
of boiling water and mixed with 1 kg of
hydraulic lime proved good.
In Auroville, India, the following coating was
used successfully for mud brick domes: the
whites of 60 eggs mixed with 2 litres of
buttermilk and 5 litres of palm liquor stirred
and mixed with 40 litres of shell lime and
4 litres of cement (Pingel, 1993).
According to various sources, the following
plant matter added to the lime also en-
hances wipe and weather resistance:

• rye flour glue (15 litres of rye flour boiled
  in 220 litres of water with the addition of
  some zinc sulphate),


• agave juice,


• boiled banana leaf juice,


• juice of the cactus opuntia,


• juice of euphorbia lactea,


• kapok oil


• raw and double-boiled linseed oil.

Cellulose glue paint

Since it is very cheap, cellulose glue mixed

with chalk powder is often used for painting

interiors. However, it offers little weather

resistance. Its wipe resistance is also low.

Bitumen coating

Bituminous emulsions offer good weather

protection for exterior walls. The following

recipe was successfully tested at the Central

Building Research Laboratory (CBRI), Roor-

kee, India: 1 part of bitumen^80 /10 0is heated

in a container with 2 parts of naphtha. This

mix is then applied with a brush to a dry

loam surface. After this coating is dry, a

second layer is applied. In order to protect

the black surface thus formed by the sun, a

final coating of lime is recommended, which

is made of 70 g of animal glue mixed into 1

kg of hydraulic lime dissolved in

0.5 litres of water (Jain et. al., 1978).

Vapour diffusion

Coatings can significantly reduce the vapour

diffusion of walls. It should be remembered

that in cold climates, the vapour barrier

effect of these coatings should be less on

the outside than on the inside.

The vapour diffusion properties of paints

available on the market are not mentioned

in their packaging, so experience is impor-

tant in judging their characteristics. Results

of tests conducted by the BRL made with

several paints, coatings, water-repellent

plasters and water repellents are shown in

12 .1.

Water penetration

The capillary water intake (see chapter 2,

p. 27) of loam surfaces is significantly influ-

100 Weather protection

12. 2

12. 3

Paint

Without

Linseed oil

Lime-casein 1:1

Lime-Casein 1:8

Silin-paint (van Baerle)

Hydrophob (Herbol)

Baysoline LD (Bayer)

Syltrit (Metroark)

BS 15 (Wacker)

Steinfestiger H (Wacker)

g/m^2

0

400

420/350

300/300

700/250/310

390/390

400/290

350/320

450/430

290/290

kg/m^2 h0.5

9.5

0.0

0.6/1.5

0.7

0.3

0.0

0.2

0.0

0.1

0.0

0.6hr/6–24hrs