Additives to clay - mineral & synthetic
Specialised Commercial Products
Specially formulated chemicals have been developed for soil stabilisation, generally for road
construction applications. The exact formulations for some are commercial secrets. The
quantities required are low, 0.1 to 1%, and best results are achieved with mechanised rather
than manual mixing. The best known are silicates – sodium silicates, soluble in water, ethyl
silicate, potassium and calcium silicate.
The need for additives
It should be noted that there is not always a need to add stabilisers. Soil properties will
dictate need and there are many examples across the world of the effective use of
unstabilised soil. Stabilisers also add significantly to cost.
If a stabiliser is deemed necessary the choice of which one to use will depend on a number of
the part of the building on which the soil is used and its exposure to the elements
the property of the soil which needs improving; e.g. dry strength, wet strength, water
erosion, abrasion resistance, surface protection, etc.
the level of improvement required
the quantity of stabiliser required
the cost and availability of the stabiliser
whether production of the stabiliser is carried out locally or whether it needs to be
The precise quantities of additives often need to be determined empirically by trial and error
for each particular situation. The results of laboratory tests often cannot be transferred
directly to field practice, although they do provide useful guidance and a starting point for
field tests. In the field, relatively simple and inexpensive tests such as observation of block
durability on soaking in water; the use of a simple press to assess the load a block can carry
in flexure can provide information on stabiliser requirements. As preparation of soil mixes
and their use for building is often carried out under less rigorous conditions than for testing a
judicious compensatory increase in stabiliser dosage is recommended.
References and further reading
Clay as a Binder Practical Action Technical Brief
Mud as a Mortar Practical Action Technical Brief
Mud Plasters and Renders Practical Action Technical Brief
Additives to Clay: Organic Additives Practical Action Technical Brief
Earth Construction, Practical Action Publishing, 1994. ISBN: 9781853391934
Building with Earth CRATerre, Mud Village Society, Delhi, India, 1990.
Building with Earth, A handbook Second Edition, John Norton, Practical Action Publishing,
Soil Preparation Equipment (product information), GTZ
Earth building materials and techniques, Select Bibliography, CRATerre, GTZ, 1991.
The Basics of Compressed Earth Blocks, CRATerre, GTZ, 991.
Appropriate Building Materials, A Catalogue of Potential Solutions, R. Stulz, K. Mukerji,
Practical Action Publishing/SKAT, 1993 ISBN 9781853392252
Stabilization of Clay Soils by Portland Cement or Lime - A Critical Review of Literature, S.
Bhattacharja, J.I. Bhatty & H.A. Todres, Portland Cement Association, Research &
Development Information, Serial No. 2066, 2003,
Compressed Earth Blocks: Vol. 1, Manual of Production, Vince Rigassi, CRATerre-EAG, GTZ,