Fly ash as a cement substitute can be used to reduce cement consumption, thereby minimizing building material costs. Another benefit obtained is the reduction of carbon dioxide (CO₂) emissions. Fly ash has pozzolanic properties, with its components containing silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), iron oxide (Fe₂O₃), and other oxides. Fly ash has lower binding strength compared to cement, but with the presence of water and alkaline activators (sodium silicate and sodium hydroxide), the silica oxide contained in fly ash undergoes a chemical reaction resembling that of cement.

One innovation that can be developed is the use of rosters as nonstructural building elements. Rosters currently produced generally use Portland cement as the binding material. In Indonesia, there are many local materials that can be used as a mixture for rosters, particularly as binding agents. One alternative binding material that can reduce the use of Portland cement is fly ash. The proportions of fly ash added (by weight) to the rosters were 0, 1.3, 1.4, 1.5, 1.6, and 1.8, with a composition ratio of 1Pc : 8Psr.

The parameters studied in this research include the material characteristics of the roster composition, such as sand gradation testing, sand specific gravity, sand silt content, sand grain conservation, and fly ash gradation; the compressive strength of the mortar forming the roster; as well as the compressive strength and water absorption of rosters with added fly ash binder at the planned composition variations.