PURPOSE: To provide the subject board containing heat-resistant rock wool, shirasu (feemiceous sand) balloon, silica sol and bonding assistant at specific ratios, having a specific gravity higher than a specific level, light weight and excellent heat-resistance, heat-insulation, nail-holding power and workability and useful as an incombustible building material.

CONSTITUTION: The objective board has a specific gravity of ≥0.3 and contains 65-80wt.% of heat-resistant rock wool, 5-20wt.% of shirasu balloon, 10-20wt.% of silica sol (in terms of SiO2) and 0.15-3.5wt.% of a bonding assistant.