and then thinned with water in a 1:5 pro-
portion. This glue should be used within
one hour (Letzner and Stein, 1987, p. 145).
Retrofitting thermal insulation with
lightweight loam
This section describes the general physical
and structural aspects that have to be con-
sidered while enhancing the thermal insula-
tion of existing exterior walls by using light-
weight loam. Different types of suitable
aggregates are described in chapter 4, p. 47.
The use of lightweight loam as infill for tim-
ber-framed houses is mentioned in chapter
9, p. 82, and highly insulating earthen wall
designs are discussed in chapter 14, p. 106.
Condensation
The later 20th century saw considerable
damage to historic timber frame houses in
Germany. Most of it occurred due to con-
densation in walls, a type of damage that
had not earlier occurred.
Much more humidity is produced in
kitchens and bathrooms nowadays than in
previous times. While today a daily warm
shower is common, earlier, people used to
wash with cold water in a basin. Further-
more, clothes were washed outside the
house in an outhouse or open area and
dried in the open. Today, clothes are usually
washed and dried within the house. All of
the above factors contribute to the produc-
tion of much higher humidity in the timber
frame house today. Also, indoor tempera-
tures are much higher nowadays in compar-
ison to earlier times. Therefore, though the
relative humidity of indoor air may be about
the same, the absolute humidity is signifi-
cantly higher. Furthermore, doors and win-
dows in timber frame houses today are
much better sealed. Therefore, the air
exchange rate is greatly reduced.
All these factors lead to a much higher con-
densation within the walls. Therefore, it is
imperative that the vapour diffusion charac-
teristics of the walls are carefully controlled.
Thermal insulation
The exterior walls of typical timber frame
houses have thicknesses of 14 to 20 cm.
The infill of the timber frame consists of
baked bricks, adobes or wattle-and-daub.
The U-value of these infills is between 2.0
and 2.7 W/m^2 K. Taking the timber frames
into account, this gives an overall U-value
of 1.2 to 2.2 W/m^2 K. Heat transmission
through these walls is thus three to six
times higher than it should be by modern
standards in moderate and cold climates.
The simplest solution, and the best in physi-
cal terms, is to increase thermal insulation
from the outside, that is to say, to envelope
the building in thermal insulation. If the
house is a historical landmark and therefore
not allowed to be covered with thermal
insulation from the outside, the additional
thermal insulation has to be applied from
the inside. This usually causes problems
because in practice, heat bridges and
vapour bridges cannot be totally avoided.
These can lead to partial moistening of the
wall because of a high degree of condensa-
tion, and subsequently to damage of the
wall surface. Furthermore, it increases the
heat loss and might lead to fungus growth.Lightweight loam layers
One possible method of applying additional
interior thermal insulation is shown in 13. 2.
Here, a formwork is fixed to spacers mount-
ed on the historic wall, and a layer of light-
weight mineral loam is poured or pumped
in. It is important that there be no space
formed between the two leaves so that the
transport of capillary water and vapour is
not hindered.
In the project shown in 13 .1, five people
took eight hours to complete 60 m^2 of this
wall, using the pumping method as
described in chapter 10, to apply a 15 to 25-
cm-thick layer of lightweight loam. Illustra-
tion 13. 3shows the finished surface of this
wall after the formwork was removed. The
material has a density of about 1000 kg/m^3.
This relatively high density was chosen in
order to get sufficient noise insulation, heat
storage and humidity balancing effects.The same method can be used to build up
exterior thermal insulation, but here, a loam
mixture with lower density is recommend-
ed.Prefabricated elements
An even simpler method of building an inte-
rior thermal insulation layer is to use prefab-
ricated loam elements like larger blocks or
panels, as described in chapter 7, or to use
lightweight loam-filled hoses as described
in chapter 10. These can be laid without
formwork in a plastic state against the wall
in one or two layers, as shown in 13. 4. In
this case it is preferable to flatten them and
fix them to the existing wall with steel wire
hooks (4 hooks per m^2 ).106 Repair of loam components13. 313. 4
13. 3Surface of a
lightweight mineral
loam wall with a den-
sity of 1,000 kg/m^3
after the formwork is
removed
13. 4Additional interi-
or thermal insulation
using hoses filled with
lightweight loam