Structural Steel Fire Retardant CoatingDuring construction, the treatment methods for the subgrade and the application of fire-resistant coatings typically involve separate subgrade and surface coatings. Here's a brief overview of the subgrade application methods.
　　
Once the initial coat is mostly dry, continue to apply additional coats in a cyclic manner until the desired thickness is achieved.
　　
Water and paint are mixed in a ratio of (0.70~0.75): tunnel fire-retardant paint, steel structure fire-retardant paint, and stir with a mixer for 20 minutes (be sure to maintain the mixing time, use the paint as it is mixed), forming a thick paste-like consistency.
　　
A small amount of paste is used to create 2.5m spaced transverse strips as thickness indicators, serving as reference for the application of tunnel fire-resistant coating and steel structure fire-resistant coating.
　　
The spraying is conducted from the middle of the tunnel towards the top (from bottom to top) using a spray gun, with each coat applied at a thickness of 3 to 8 mm.
　　
Upon completion of the grassroots work, the surface of the coating is required to be smooth, glossy, and clean. Due to the insufficient smoothness of the spray surface, after one coat is applied, it is necessary to immediately use paste for manual补filling and leveling, as well as trimming, to ensure the coating surface is smooth and flat, and to guarantee the coating achieves the designed thickness.
　　

After the base treatment of fire-retardant coatings, it is crucial to control the environmental conditions within 24 hours to ensure the quality of the tunnel fire-retardant coating.