Civil Engineering Reference
In-Depth Information
Lime render
A normal lime render consists of slaked lime, sand and water. The proportion of
lime to sand is 1:3 by volume. The render is put on in several layers until it is
about 1.5 cm thick. It is most suitable for internal use, e.g. in bathrooms, but can
also be used externally. For exterior use it should be protected against driving
rain and continuous damp, otherwise it may be destroyed by frost because of its
high porosity.
Nepalesian lime rendering
A render from Nepal should guarantee frost-resistance! The mixture consists of 15 kg lime,
6 kg of melted ox tallow and 36 litres of water. The tallow is for the waterproofing. The mixture
has to be left for 24 hours at a low temperature. The water left on the surface is then poured
away, and the creamy mixture at the bottom is mixed with 3 kg quartz sand. The render is
applied in layers 3-5 mm thick. Curing takes weeks, and the surface must be protected during
this period. The mixture is waterproof and weather-resistant, and is used externally on earth
domes. (Minke, 1984.)
Lime rendering on earth walls
A condition for the use of lime render on earth walls is that the walls are well dried, and
that the surface is even and without cracks. A thin clay gruel is applied to the wall and
given a rough surface as a key for the lime rendering. The gruel consists of one part clay
gruel and two parts sand with a grain size of around 4 mm. Pieces of hacked straw or hay
3 cm long are added and the mixture is then applied in two layers, straight after each
other. The first layer is about 2 mm thick and the other is 5-8 mm thick. This is then left
for two to three days.
The lime render is applied in two layers by trowel, without dampening the surface
before application. The first layer consists of one part slaked lime, one part sand with a
grain size of 4 mm and three parts hemp fibre or the equivalent, which is 5 mm thick. The
next layer is 2 mm thick and consists of one part finely-sieved lime dough and three parts
marble powder. In Japan, where this render originates, a small percentage of gelatine
from seaweed is added. This makes the surface waterproof, although it is not vapour-
proof.
For coloured render, pigment is added in the second layer (see Table 18.1). The sur-
face is matt from the beginning, but a smooth shiny surface can be achieved by adding
a third layer that is only 1 mm thick, consisting of one part fine-sieved slaked lime, one
part white marble dust and one part pigment. The thin layer of render is put on with a
trowel and smoothed out until it gels to a lustre. Then the surface is polished for one to
two hours with the palm of the hand. This is obviously a very labour-intensive proce-
dure.
Lime pozzolana render
A hydraulic lime or lime pozzolana cement gives a more weather-resistant ren-
der. It still needs to be applied in several layers to achieve a high durability. The
first layer consists of one part hydraulic lime and two parts sand with a grain size
of up to 7 mm. The second layer consists of one part hydraulic lime and three
