Can galvanized fireproof iron sheet be directly used for exterior curtain walls or roofs?
Publish Time: 2025-12-09
In modern architecture, fire safety and aesthetic durability are increasingly becoming core design considerations. Galvanized fireproof iron sheet, due to its combination of metallic strength and certain fire resistance, is often considered for use in building envelopes, such as curtain walls or roof systems. However, whether it can be directly exposed to the outdoor environment for long-term use requires in-depth examination from three aspects: material properties, environmental adaptability, and functional integrity.Firstly, the presence of a galvanized layer does indeed give the steel sheet excellent corrosion resistance. Zinc, acting as a sacrificial anode, preferentially oxidizes in humid or oxygen-containing environments, thus protecting the internal iron matrix from rust. This characteristic makes galvanized steel sheets widely used in outdoor applications such as roofs and walls. However, it is important to note that "galvanizing" is not equivalent to "permanent rust prevention." In coastal areas with high salt spray, industrial areas with high sulfur content, or areas with frequent acid rain, the zinc layer will be consumed more quickly; if the coating is thin or the process is uneven, exposed cuts, drilled holes, or scratches are more prone to electrochemical corrosion points, leading to the spread of localized rust. Prolonged exposure not only affects aesthetics but may also weaken the structural strength of the sheet metal, indirectly impacting the integrity of its fire-resistant coating function.Secondly, the method by which fire resistance is achieved determines its suitability for exposed use. If the galvanized steel sheet itself constitutes a fire-resistant system (e.g., meeting fire resistance time limits through specific thickness and construction), its surface can be directly exposed. However, in many cases, galvanized steel sheets serve only as the supporting framework or protective shell of the fire-resistant system, with the actual fire resistance relying on embedded fire-resistant rock wool, intumescent coatings, or other insulation materials. In such cases, using galvanized sheets alone for exterior curtain walls or roofs, while providing some fire resistance, may not meet the required fire resistance limits, posing safety hazards.Furthermore, ultraviolet radiation, thermal expansion and contraction, and weathering pose challenges to long-term performance. Although the metal itself is not degraded by ultraviolet radiation, if an organic coating (such as color-coated steel) is subsequently applied to the surface, prolonged exposure to sunlight may cause the coating to chalk, fade, or peel off, thus accelerating the aging of the substrate. Meanwhile, metals repeatedly expand and contract due to diurnal temperature variations. If expansion joints are not provided during installation or rigid fixing is used, stress deformation and joint cracking can easily occur, compromising the overall airtightness and waterproofness, and even affecting the continuity of fire-resistant partitions.Furthermore, architectural aesthetics and maintenance costs cannot be ignored. Untreated galvanized steel sheets have a silver-gray metallic luster, which, while possessing an industrial aesthetic, may develop white rust (basic zinc carbonate) or black spots over time, affecting the visual effect. If the project has high requirements for appearance consistency, additional surface treatments are necessary, such as spraying fluorocarbon paint, film coating, or using pre-coated color steel sheets. This involves issues such as the adhesion and weather resistance compatibility between the coating and the galvanized layer.It is worth noting that standards and certifications are key criteria. Many national building fire protection standards clearly distinguish between "structural fire protection" and "enclosure system fire protection," stipulating that exposed components must simultaneously meet fire resistance, weather resistance, and mechanical performance requirements. Simply relying on galvanized iron sheets as the main material for exterior curtain walls or roofs may fail fire safety inspections if relevant weathering resistance tests (such as salt spray and damp heat cycling) and overall fire protection system certification are not passed.In summary, while galvanized fireproof iron sheets can be used for exterior curtain walls or roofs under specific conditions, they are not a "ready-to-use" solution. A systematic design is required, taking into account specific climatic conditions, fire resistance ratings, supporting construction methods, and surface protection measures. A truly reliable fireproof exterior wall solution finds a balance between the strength of metal and natural corrosion, ensuring safety, durability, and aesthetics—allowing the fireproof shield to withstand the test of time.
