Galvanized sheet has a certain degree of waterproof ability, but strictly speaking, it cannot be defined as a completely waterproof material. Galvanized sheet is a metal sheet made of cold-rolled or hot-rolled steel plate as the substrate, with a layer of zinc coating on the surface. The zinc layer acts as a protective film, which can isolate moisture from direct contact with the substrate, slow down the process of oxidation and corrosion, and effectively prevent rusting of the substrate in general humid environments or short-term rainwater erosion. However, if it is exposed to stagnant water for a long time, the zinc layer is damaged, or it is corroded by highly corrosive liquids, its waterproof performance will significantly decrease. Next, this article will delve into the waterproof characteristics of galvanized sheet, analyzing in detail its composition, waterproof principles, and factors that affect waterproof performance.

1. Basic composition of galvanized sheet

Galvanized sheet is a sheet made by coating a layer of zinc metal on the surface of ordinary steel plate. This zinc layer not only provides additional protection for the steel plate, but also affects various properties of the galvanized sheet to a certain extent, including waterproof performance. Zinc itself has good chemical stability and is not easily reacted violently with oxygen, moisture, and other substances in the air at room temperature, which lays the foundation for galvanized sheets to have certain waterproof capabilities.

2. Waterproof principle of galvanized sheet

1. Physical barrier effect

The zinc layer on the surface of the galvanized sheet forms a physical barrier that can effectively prevent moisture from directly contacting the steel substrate. When there is water present in the external environment, the zinc layer first comes into contact with water, preventing water from corroding the steel plate. Zinc has a high density and relatively compact texture, which makes it difficult for moisture to penetrate the zinc layer and reach the interior of the steel plate, thus protecting the steel plate from water damage to a certain extent.

2. Chemical protection effect

Zinc is an active metal, but its chemical properties are relatively stable. In the presence of water, zinc undergoes a slow chemical reaction with substances such as oxygen in the water, forming a dense zinc oxide film on the surface of the zinc layer. This layer of zinc oxide film has good adhesion and stability, which can further prevent moisture and oxygen from penetrating into the interior of the zinc layer, thereby delaying the corrosion rate of the zinc layer and indirectly protecting the steel plate from water corrosion. Moreover, even if the zinc layer is locally damaged, the exposed steel plate will slow down corrosion due to the electrochemical protection formed with zinc. This electrochemical protection effect also helps to maintain the waterproof performance of galvanized steel to a certain extent.

3. Factors affecting the waterproof performance of galvanized sheet

1. Zinc layer thickness

The thickness of the zinc layer is one of the key factors affecting the waterproof performance of galvanized sheet. Generally speaking, the thicker the zinc layer, the stronger its physical barrier and chemical protection effects. A thicker zinc layer can provide more durable protection and prolong the time for moisture to penetrate the zinc layer and reach the steel plate. For example, under the same environmental conditions, galvanized sheet with a zinc layer thickness of 20 μ m has better waterproof performance than galvanized sheet with a zinc layer thickness of 10 μ m, and can more effectively resist water erosion. The following table shows the comparison of waterproof performance of galvanized sheets with different zinc layer thicknesses:

Zinc Layer Thickness (μm)	Estimated Waterproof Lifespan (Years)	Waterproof Performance Description
5	3 - 5	Under general environmental conditions, it can resist moisture erosion in the short term, but the zinc layer is consumed relatively quickly.
10	5 - 8	The waterproof performance is improved, and it can handle medium-humidity environments. The consumption rate of the zinc layer is moderate.
15	8 - 12	It has good waterproof performance in various environments, and the zinc layer can provide protection for a relatively long time.
20 and above	Over 12 years	It has excellent waterproof performance and can adapt to relatively harsh humid environments. The zinc layer provides long-lasting protection.

2. Environmental factors

Humidity: Environmental humidity has a significant impact on the waterproof performance of galvanized sheet. In high humidity environments, the moisture content in the air is high, making it easier for moisture to adhere to the surface of galvanized sheets, accelerating the reaction between the zinc layer and water. Long term exposure to high humidity environments, even if the zinc layer is thick, may lead to a decrease in waterproof performance due to frequent contact with water. On the contrary, in low humidity environments, the chance of galvanized sheet coming into contact with water is reduced, and its waterproof performance can be better maintained.
Temperature: Temperature changes can also affect the waterproof performance of galvanized sheets. Under high temperature conditions, water evaporation accelerates, but at the same time, it may accelerate the chemical reaction rate between the zinc layer and certain substances in the water, leading to accelerated consumption of the zinc layer. Under low temperature conditions, the chemical reaction rate slows down, but it may cause moisture to condense on the surface of the galvanized sheet, increasing the contact time between moisture and the zinc layer. Therefore, the waterproof performance of galvanized sheet will vary under different temperature conditions.

Corrosive medium: If there is a corrosive medium in the environment, such as acidic or alkaline gases or liquids, it will accelerate the corrosion of the zinc layer, thereby weakening the waterproof performance of the galvanized sheet. For example, near a chemical plant, the air contains acidic gases, and the zinc layer on the surface of galvanized sheets will corrode faster, resulting in a rapid decrease in waterproof ability.

3. Processing technology

The processing technology of galvanized sheet also has an impact on its waterproof performance. During the galvanizing process, improper process control may result in weak bonding between the zinc layer and the steel plate substrate, leading to issues such as zinc layer detachment and blistering. These issues can damage the integrity of the zinc layer, allowing moisture to directly come into contact with the steel plate and reducing the waterproof performance of the galvanized sheet. In addition, during the subsequent processing of galvanized sheet, such as cutting, bending, etc., if the zinc layer is damaged due to improper operation, it will also affect its waterproof effect.

4. Waterproof performance of galvanized sheet in different scenarios

1. Construction field

In the field of construction, galvanized sheet is commonly used for roofs, walls, and other parts. In general building environments, if the humidity is moderate and there is no strong corrosive medium, galvanized sheet, with its own waterproof performance, can effectively prevent rainwater infiltration and protect the building structure from water erosion. For example, in some ordinary industrial plants and civil buildings, galvanized sheet is used as the roof material, and after years of use, it can still maintain a good waterproof state. However, in coastal or high humidity areas, due to the harsh environment, the waterproof performance of galvanized sheet may be challenged to some extent, and additional protective measures such as applying waterproof coatings need to be taken.

2. Manufacturing field

In the manufacturing field, galvanized sheet is used to make various containers, equipment casings, etc. In these applications, the waterproof performance of galvanized sheet is crucial for ensuring product quality and service life. For example, making containers for storing liquids, if the waterproof performance of galvanized sheet is poor, the liquid may leak, causing product damage or posing a safety hazard. Therefore, in the manufacturing field, high waterproof performance is required for galvanized sheets, and galvanized sheets with thicker zinc layers and better quality are usually chosen.
Galvanized sheet has certain waterproof performance, mainly due to the physical barrier and chemical protection provided by the zinc layer on its surface. However, the waterproof performance of galvanized sheet is not absolute and is affected by various factors such as zinc layer thickness, environmental factors, and processing technology. In practical applications, we need to select galvanized sheets with appropriate zinc layer thickness according to specific usage scenarios and requirements, and pay attention to the impact of environmental factors on their waterproof performance. At the same time, reasonable processing technology and subsequent maintenance can also extend the waterproof life of galvanized sheet, ensuring its good waterproof effect in practical applications. By comprehensively understanding the waterproof performance and related influencing factors of galvanized sheet, we can use galvanized sheet more scientifically and reasonably to meet the needs of different fields.