PURPOSE: To obtain the subject coating liquid giving a coating film having high hardness and free from crack even at large thickness without causing environmental or safety problem by compounding an aqueous solution containing a specific alkali metal silicate with a silicone soluble in alkaline water at a specific ratio.

CONSTITUTION: The objective coating liquid is produced by compounding an aqueous solution containing an alkali metal silicate of the formula (R is Na and/or K; (m) is 1-3; (n) is 4-10) with a silicone soluble in alkaline water (e.g. aqueous solution of sodium methylsiliconate) in an amount of 3-100 pts.wt. of the solid component of the silicone based on 100 pts.wt. of the solid component of the aqueous solution. Preferably, 0.5-3wt.% (based on dry film) of one or more kinds of substances selected from boric acid, Zn2+ and Al3+ are dissolved in the aqueous solution of alkali metal silicate.