The invention disclosed is a fire resistant inorganic coating composition which intumesces when subject to high temperatures to form a substantially continuous heat insulating structure and retains this structure for prolonged periods at temperatures up to 1000.degree. C. The coating composition comprises______________________________________ Parts by Weight ______________________________________ sodium silicate (aqueous solution) 40-70 potassium silicate (aqueous solution) 40-70 silicon carbide powder 3-15 ______________________________________ A composite fire-protective coating system is also disclosed which comprises a plurality of coatings sequentially applied to the substrate, typically aluminum, to be protected. Specifically, a first heat resistant, substantially air impermeable bonding layer and an inorganic intumescent layer as described above. An additional heat resistant air impermeable layer may be included as a top coat. Some applications may require an additional inorganic intumescent layer.