Building with earth - Gernot MINKE (1)

If the surface of the walls demands a plaster
thicker than 15 mm, this should be applied
in two layers, with the ground layer containing
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 fatfree
white cheese, borax, urea, sodium
gluconate and shredded newspaper (which
provides cellulose fibre and glue). The following
mixes worked well:
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
Lime reacts with the casein within the fatfree
cheese to form a chemical waterproofing
agent. A similar reaction is obtained with
lime and borax (which is contained in shredded
newspaper). Sodium gluconate acts as
a plasticiser, so that less water needs to be
mixed for preparation (thereby reducing
shrinkage). Urea raises compressive and tensile
bending strength, especially with silty
soils (see chapter 4, p. 43).
Shredded wastepaper leads to better workability
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.
5
0.2
(1)
all proportions are stated in volumetric terms
(2)
made of 1 part clayey soil and 2 parts sand
A B C D E
10
25
5
0.2
10
25
10
25
(3)
treated with borax content
(4)
made of 4 parts fat-free cheese and 1 part hydraulic lime mixed intensively
for 2 minutes
1
5
1
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 necessary
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 permeates
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 shrinkage
cracks.
11.6
11.5
94
Loam plasters