The intention of surface coating is to improve the lifespan of the hazardous liquid storage tank to avoid the catastrophic failure by corrosion or leakage. Water or oxygen present inside the storage tanks tends to permeate through the substrate because of the poor adhesive properties, leading to corrosion, leakage, etc. Recently, polyurea (PU) has been widely used as a surface coating to protect the material under various harsh loads and climatic conditions. However, ultimate variation in the efficiency of PU coating is with respect to various coating process parameters. Herein, the plural spray coating process parameters, namely mixing ratio, temperature, coating pressure, and stand-off distance on the bonding strength of PU coating with steel and aluminium, were optimized. Furthermore, with the help of the Taguchi method, the optimum process parameters and their corresponding levels were identified, and it was found that each response has a different best process parameter. To circumvent this, Grey relational analysis (GRA) was carried out, and it has improved the overall efficiency of both the substrates by nearly 10 %.