To ensure their continued popularity and sales, ceramic stoves should not fail in use and should be sufficiently strong to withstand the mechanical loads and knocks they are subjected to. Failures caused by thermally-induced stress occur more in stoves made in some locations than others. This manual details the findings of a research project which studied a number of different clays from locations throughout Asia and Africa to try to see why this should be, and found a strong correlation between the clay/non-clay ratio and the tendency of stoves to fail in service. The project went on to develop a method of clay testing, the clay/non-clay ratio measurement technique, which will reduce the chance that stoves will fail through thermally-induced stress. This manual is intended to be of use to those working in stove projects or who are engaged in the manufacture of ceramic stoves, and who have come across the problem of cracks and breakages which occur while the stove is in use. It offers clear explanations of some of the causes of these problems and straightforward methods of avoiding them.