Bottom ash from coal-fired power plants is a potential raw material for the production of ceramic tiles, bricks and blocks for various applications. In this work we are presenting a novel microwave method to utilize the bottom ash to produce thermal insulating bricks. Foam samples were prepared by microwave foaming of the mortar prepared by milling the bottom ash, sodium silicate and NaOH. The microwave foaming ability of different slurry compositions and the physical and mechanical properties of the foamed samples were evaluated. FTIR analysis reveals that the degree of geopolymerization increases with increasing fraction of sodium silicate. Foams with low bulk density, high porosity, low thermal conductivity and compressive strengths were obtained by this method. With varying the bottom ash to sodium silicate ratio, it is possible to modulate the physical and mechanical properties of the insulating bricks. (C) 2014 Elsevier B.V. All rights reserved.