Mud as a mortar
Practical Action
and the time spent on building have necessitated a more rigorous scientific understanding of
soil properties to enable optimum use to be made of local soils.
In addition, mud mortars are liable to increased erosion and loss in strength if used in humid
or wet conditions. For this reason they need protection from such conditions by appropriate
building design, by using them with complimentary water-resistant materials or by
incorporating special protective materials and structures in the building.
Improvements to mud mortars
Although measures to improve the durability of earth as a building material, as well as
building techniques with earth with very low level of risk of failure, have been well-
documented, to a large extent based on recent research work, it is always worthwhile to study
traditional building practices in a particular area.
Problems with earth-based buildings can generally be avoided by regular maintenance -noting
any parts of the building which have become weakened or eroded and immediately repairing
them before any more serious problems develop. However maintenance requirements of mud
based mortars can be reduced by incorporating special protective measures in the design of
the building and by avoiding use of mud mortars in the more exposed parts as well as by
improving the performance of the mortars themselves.
Protective measures
These include provision of:
water-resistant copings or overhanging roofs
A water-resistant foundation and wall base, possibly complemented by a damp-proof
course to prevent moisture penetrating the mud mortar
Rendering any exposed walls with a mortar which allows passage of water vapour.
This facilitates drying and thus reduces the risk of loss of bond between the render
and the wall. Otherwise, if passage of water vapour through the mortar is too slow,
some other means of anchoring the render to the wall would be needed, such as wire
mesh or netting, or steel nails
Repointing of mortar on the outside 1.5 to 3 cm of joints with a more water resistant
material
Improved performance
Performance of mud mortars can be improved with various additives such as:
straw, which reduces the shrinkage considerably without decreasing the bond
strength much;
sand, which reduces shrinkage but also reduces the bond strength;
cement, which increases bond strength and also somewhat reduces the shrinkage,
although while reducing the incidence of microcracks it does increase the likelihood
of major structural cracks, appearing every 4 to 6 metres - but these can be
compensated for by inserting shrinkage joints every 4 to 6 metres.
A number of other additives can be used and further information is given in the
accompanying leaflets “Additives to Clay".
Testing mud mortars
It is advisable to carry out tests on the mortars before using them in construction. If similar
mortars have already been used for building in the area, and the soils used and methods of
preparation can be identified, then it can simply be a matter of checking on the performance
of those mortars.
Without such information test samples need to be prepared. Ideally test walls should be built
and left in actual exposure conditions for some time, but a minimal exposure test can be
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