Building with Earth: Design and Technology of a Sustainable Architecture

Loam plasters consist mainly of sand and

silt with only as much clay as is necessary

(usually between 5% and 12%) for develop-

ing their adhesive and binding forces. It is

difficult to determine the proportions of an

ideal loam plaster, because not only the pro-

portions of clay, silk and sand influence a

mixture’s properties. Other factors affecting

the composition are the grain size distribu-

tion of the sand fraction itself, the water con-

tent, the type of clay, the method of prepa-

ration and the additives. In order to test the

appropriateness of loam plasters, samples

with varied compositions should be tested.

If the surface is rough enough, then loam

plasters stick well not only to loam surfaces,

but also to those made of brick, concrete

and stone. For the ability of loam plasters to

balance indoor air humidity see chapter 1.

Preparation of ground

As loam plaster does not react with the

ground chemically, the surface has to be

sufficiently rough in order to develop a

good physical bond. If masonry is to be

plastered, especially when using larger and

very smooth bricks, it is recommended that

a 45° groove be cut with a trowel into the

joints, as shown in 11.1. Another method of

obtaining a good bond when rammed loam

walls are to be plastered is to wet them suf-

ficiently until surfaces are soft, and to then

scratch diagonal patterned grooves into

them with a small rake or a nail-trowel (11. 2

and 11.3).

In order to ensure that the plaster adheres

well, plaster supports can be applied in the

form of galvanised wire mesh, plastic mesh,

reed mats etc.

Composition of loam plaster

In order to keep loam plaster free of shrink-

age cracks, the following points must be

kept in mind:

• The loam should contain enough coarse
  sand.

92 Loam plasters

11 Loam plasters

11. 2 11. 3

11.1