A method for determining the optimum number of conditioning wafers to be run following a wet clean of the walls of an RF plasma chamber 1 is based on an electrical precursor signal. Polymer build up on a plasma chamber wall during normal chamber conditioning is monitored by observing components of the fundamental RF signal. After a pre-determined number of wafers has been run, a predictive model is used to determine the total number of wafers needed to complete the conditioning cycle.