A liquid applied, silicone-based air and water barrier coating composition and its use as a silicone-based air and water barrier is provided. The barrier is generally vapour permeable and suitable for the construction industry. The liquid coating composition generally has a shelf-life of at least 15 months. The liquid coating composition comprises: (i) a crosslinked polysiloxane dispersion comprising (c) a surfactant and (d) water; (ii) one or more rheology modifiers in an amount of from 0.25 to 5 wt. % of the composition; and (iii) an acidic pH stable colloidal silica in an amount of from 15 to 30 wt. % of the composition; and optionally (iv) one or more stabilizers.