The present invention relates to a fire-resistant coating and method thereof, which confers enhanced flame and heat resistance to substrate such as building materials. The invented coating is especially applicable to cellulose-based building materials including but not limited to fiberboards, wallboards, roofing materials, particleboards, ceiling tiles, soundproofing boards and hardboards. This novel composition is also useful in providing a fire-resistant coating for concrete, metals, foamed polymeric materials, gypsum and other substrates. A preferred embodiment generally comprising: mono potassium phosphate, magnesium oxide, silica powder, calcium silicate, rice hull ash and water. A method for imparting fire-retardancy to substrates using the invented composition is also described.