Building with Earth: Design and Technology of a Sustainable Architecture

If the surface of the walls demands a plaster
thicker than 15 mm, this should be applied
in two layers, with the ground layer contain-
ing more clay and coarse aggregates than
the second one. If the ground layer acquires
shrinkage cracks, this is not problematic,
and it might even be beneficial by providing
a better bond to the final layer of plaster.
Adding rye flour improves the workability of
the plaster and enhances the resistance of
the surface against dry and moist abrasion.
Through testing, the author of this book
has proven that such resistance can also
be built up by adding casein glue made of
1 part hydraulic lime and 4 to 6 parts fat-
free white cheese, borax, urea, sodium
gluconate and shredded newspaper (which
provides cellulose fibre and glue). The fol-
lowing mixes worked well:

Lime reacts with the casein within the fat-
free cheese to form a chemical waterproof-
ing agent. A similar reaction is obtained with
lime and borax (which is contained in shred-
ded newspaper). Sodium gluconate acts as
a plasticiser, so that less water needs to be
mixed for preparation (thereby reducing
shrinkage). Urea raises compressive and ten-
sile bending strength, especially with silty
soils (see chapter 4, p. 43).
Shredded wastepaper leads to better work-
ability and reduces shrinkage. The mixes B, C
and E exhibited the best workability. When
using mixes A and E, it is best to begin by
mixing the casein glue and the shredded
newspaper together with the water and
adding loam and sand after an hour.

With all mixes, it was found that when the

final smoothing was executed using a felt

trowel, it was best to wait several hours or

even a day.

Guidelines for plastering earth walls

Since pure loam plaster does not react

chemically with the ground, it might be nec-

essary to treat the ground so that sufficient

curing can occur. In doing so, the following

guidelines should be kept in mind:

1. The earth surface to be plastered must
   be dry enough so that additional shrinkage
   does not occur.


2. All loose material should be scraped off
   the surface.


3. The ground should be sufficiently rough
   and, if necessary, moistened and grooved
   or the mortar joint chamfered, as described
   above in this chapter.


4. Before plastering, the ground should be
   sufficiently moistened so that the surface
   softens and swells and the plaster perme-
   ates the soft layer.


5. The plaster should be thrown with strong
   impact (slapped on) so that it permeates
   the outer layers of the ground and achieves
   a higher binding force due to the impact.


6. If the plaster has to be more than 10 to
   15 mm thick, it should be applied in two
   or even three layers in order to avoid shrink-
   age cracks.

94 Loam plasters

11. 5


12. 6

Components Mix(1)

Loam slurry (2)

Sand (0–2)

Shredded newspaper(3)

Casein glue(4)

Fat-free cheese

Urea

Sodium gluconate

10

25

1

10

25

5

0.2

10

25

5

0.2

10

25

5

1

10

25

1

A B C D E

(1)all proportions are stated in volumetric terms
(2)made of 1 part clayey soil and 2 parts sand
(3)treated with borax content
(4)made of 4 parts fat-free cheese and 1 part hydraulic lime mixed intensively
for 2 minutes