A new model based on experimental observation is developed for the build-up of disordered material in ion bombarded silicon. The model assumes that disordered zones are created in a background of migrating point defects, these zones then act as neutral sinks for such defects which interact with the zones and cause recrystallization. A simple steady state rate theory is developed to describe the build-up of disordered material with ion dose as a function of temperature. In general the theory predicts two distinct behaviour patterns depending on the temperature and the ion mass, namely a linear build-up with dose to complete disorder for heavy bombarding ions and a build-up to saturation at a relatively low level for light ions such as protons. However, in some special circumstances a transition region is predicted where the build-up of disorder approximately follows a (dose)frac12;relationship before reverting to a linear behaviour at high dose.