In order to investigate the effects on intumescence to fire protective coatings, the characteristics of solubility, hygroscopic nature and X-ray diffration results on soluble silicate were determined. Solubility is depended on the mutual action of each silicate. In the result of hygroscopic characteristics by water absorption under several kinds of relative humidity, lithium silicate is more stable than sodium and potassium silicate over moistures. Eventhough free water is evaporated over $100^{circ}C$ , physically adsorption water and ionic water are eliminated about $200^{circ}C$, but evolution of structural water is expected to be emitted between 400~$600^{circ}C$ range. Those are considered to be contributed intumescence on soluble silicate.