Building with earth - Gernot MINKE (1)

12 Weather protection of loam surfaces
Loam surfaces need not always have additives
in to be made weather-resistant. It is
often sufficient to protect or harden them
with plaster or paint. This chapter describes
the different ways loam surfaces can be
made more resistant to environmental
forces, and the structural measures required
to shelter them from these forces.
Consolidating the surface
The simplest method of hardening the surface,
especially against rain and wind erosion,
is to consolidate it. This can be done
by rubbing a metal trowel with high pressure
onto the surface when it is moist and
slightly pliable. Traditional Indian and African
methods employ flat but light convex stones
that are rubbed in a circular motion across
the surface with great force. The treatment
is adequate if the surface appears shiny and
no pores or cracks are visible. While this
leaves the composition of the material unaltered,
it nonetheless creates a surprisingly
high degree of weather resistance.
Paints
Paints on exposed loam surfaces have to
be renewed periodically. The paint can be
physically eroded by wind, frost or rain, or
chemically eroded by ultraviolet radiation or
acid rain. External paints should be simultaneously
water-repellent and, especially for
cold climates, porous, i.e., should contain
a coherent net of micro-pores that allow
vapour diffusion to the outside. Latex and
dispersion paints, therefore, are not recommended.
For information supplementing that contained
in this chapter, see Wehle (1985).
Preparation of ground
If the ground is very silty and lime-based
paints are used, the surface should be
primed with thin lime-casein milk and then
rubbed. The primer can be made of two
parts of hydraulic lime, one part fat-free
white cheese and 15 parts water.
Recommended paint mixtures
Pure lime wash
The lime wash mixture has to be very thin,
allowing the paint to penetrate deeply
enough into the ground so that flaking does
not occur during drying. Therefore, three or
even four thin coats are recommended, with
the first coat being the thinnest. The mix can
be made from 50 kg hydraulic lime dissolved
in 60 litres of water. It is often preferable
to add 1 to 2 kg of kitchen salt; being
hygroscopic, the salt allows the mixture to
remain moist longer, thereby ensuring better
curing of the lime. Pure lime wash is perfectly
white when dry, but can be toned
down by adding clay or loam powders or
other lime-proof earthen pigments. Pure
lime wash is not wipe-resistant.
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Weather protection