Fly ash is an industrial waste general obtained from coal plant.Fly ash (i.e. from Mae Moh power plant, Lampang) is normally used as partial replacement of Portland cement for making of concrete owing to its high production rate ; however, numerous tones have needed the well waste management. Recently,many researchers have achieved the use the fly ash as the source material for geopolymer production.This material was prepared by mixing fly ash with alkaline solution at low temperature resulting in an alumino-silicate compound. It provides the good physical and mechanical properties including the resistance in acid solution. In addition, it has found that cement-based composites (e.g. cement sewagepipe) are not resistant to acid condition leading to the instability of material. Therefore,this research investigated the application of fly ash geopolymer as coating material. This materil was coated on the cement-based composite and immersed into the 0.005% H2SO4 (pH = 3) representing the pH of industrial wastewater,and 3% H2SO4 (pH = 3) representing thr worst condition in the wastewater system. pH and Ca2+ content of immerased solution were monitored. Hardness testing of geopolymeric coating material was also performed.