Sludge production is an unavoidable consequence of wastewater treatment and creates problems for disposal. For highly urbanized cities, incineration of sludge might be a viable solution for sludge disposal. Incineration of digested and dewatered sludge, yields an odourless, cellular, porous mass of sludge ash with low unit weight. In the present study, a comprehensive test programme was developed to examine the potential for using the pulverized sludge ash as a cement substitute in mortar. Sludge ash used as replacement for 5, 10, 15 and 20 percent by weight of the cement. The results show that initial and final setting times are longer with an increase of pulverized sludge ash. Effects of pulverized sludge ash on the Le Chatelier expansion and specific surface area of mortar are not significant. The test samples cast were cured for periods of 3, 7, 14 and 28 days before testing for corapressive and tensile strength. The strengths for the mortars at different ages decrease with the increase of sludge ash. However, with 10 percent replacement of cement by sludge ash, the 28th day compressive and tensile strength for the mortars are similar to conventional mortar. © 1994 Publication Division Selper Ltd.