To manufacture a wood ash ceramic, at a low cost and in large quantities from an industrial waste, which is an artificial rock close to an igneous rock (acidic rock) substance containing particularly a large amount of SiO2 among environmentally friendly natural rocks, and which has a low specific gravity, good compressive and bending strength, and good water-absorbing properties, and which does not cause freezing and thawing which causes problems in a cold area.

The method for manufacturing the wood ash ceramic comprises: a step of blending and kneading wood ash sludge of approximately 17-30 wt.% with a clay of approximately 70-83 wt.% so as to be composed of SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O and TiO2 contained in the igneous rock (the acidic rock); a step of forming the mixture into a molding; and a step of firing the dried molding at about 900-1,200°C. The blending ratio of the wood ash of approximately 17-30 wt% is determined in consideration of the blending of the ingredient ratio of SiO2 as well as a balanced selective utilization of the industrial waste. As blended, kneaded and fired, the wood ash ceramic is rich in moldability and can be used as a building material, an interlocking material, a planting strip, a seaweed fish-breeding reef, a multi-natural bank protection block of a river, and a block laid in a fish farming pool.