- To reduce shrinkage cracks while drying,
the mortar should contain sufficient quanti-
ties of coarse sand as well as fibres or hair.
- To improve surface hardness, cow dung,
lime, casein or other additives should be
added to the top layer (see chapter 4, p. 40
and p. 47).
- In order to provide surface hardness and
resistance against wet abrasion, the surface
should be finished with a coat of paint.
- When using plasters, changes in the
physical properties of materials caused
by additives and coatings should be kept
in mind, especially with respect to vapour
diffusion resistance.
Sprayed plaster
In 1984, the author of this book successfully
developed a sprayable lightweight loam
plaster with high thermal insulation, contain-
ing shredded newspaper. This plaster can
be applied even in a single layer up to
30 mm thick using an ordinary mortar pump
(11. 5). In order to shorten the curing period,
high-hydraulic lime and gypsum were
added to the mixture. Other lightweight
sprayable plasters used to fill the frames of
timber-framed houses and skeleton struc-
tures are described in chapter 9, p. 81.
Lightweight mineral loam plaster
Illustration 11. 6shows the surface of an
8-mm-thick loam plaster with expanded
clay aggregates 1 to 4 mm in diameter. To
reduce curing time and increase vapour dif-
fusion resistance, the plaster was stabilised
with 5% high-hydraulic lime. It is not easy
to smooth the surface with a trowel, since
the aggregate tends to come out during
the process. To avoid this, shredded paper,
cellulose fibres or casein-glue can be added
into the mix.
Thrown plaster
Illustrations 11. 7and 11. 8show how a tra-
ditional African technique, consisting of
throwing loam balls onto a wall, has been
adapted. Here, this technique is used on a
wood-wool board for the wall of a winter
garden, described in chapter 14, p. 129. In
order to increase adhesion, bamboo dowels
were hammered halfway into the board.
Plastered straw bale houses
Straw bale houses, known since the end of
the 19th century when the first example
was built in Nebraska, USA, found a renais-
sance in the 1980s. Meanwhile, a lot of new
houses with straw bale walls were built in
95 Loam plasters
- 5Spraying light-
weight loam plaster
- 6Lightweight loam
plaster with expanded
clay (1–4 mm)
11.7 to 11.8Thrown
plaster in a winter
garden
11. 8
- 7
