Thick steel structure fire retardant coating refers to the coating thickness is greater than 7 mm, less than or equal to 45 mm, granular surface, small density, low thermal conductivity, fire resistance limit of more than 2 h steel structure fire retardant coating. Since the composition of thick fire retardant coatings is mostly inorganic materials, its fire performance is stable and the long-term use effect is good, but the particles of its paint components are large, the appearance of the coating is uneven, affecting the overall beauty of the building, so it is mostly used for structural concealed engineering. This kind of fire retardant coating uses the granular surface of the material in the fire, the density is small, the thermal conductivity is low or the heat absorption of the material in the coating, which delays the temperature rise of the steel and protects the steel . This kind of fireproof coating is made of suitable inorganic binder (such as water glass, silica sol, aluminum phosphate, refractory cement, etc.), Then it is mixed with inorganic lightweight adiabatic aggregate materials (such as expanded perlite, expanded vermiculite, sea bouldering, floating beads, fly ash, etc.), fire retardant additives, chemical agents and reinforcement materials (such as aluminum silicate fiber, rock wool, ceramic fiber, glass fiber, etc.) and fillers, etc., which has the advantages of low cost. Spraying is often used in construction, which is suitable for indoor and outdoor concealed steel structures with fire resistance limits of more than 2 h, high-rise all-steel structures and multi-storey factory steel structures. For example, the fire resistance limit of the columns of high-rise civil buildings, general industrial and civil buildings supporting multi-layer columns should reach 3h, and the thick fireproof coating should be used to protect them.