When it comes to metal raised garden bed, fortunately, steel is actually a very food-safe material for your raised bed. Steel is also incredibly durable, sustainable and beautiful. However, steel tends to rust when exposed to moisture, which makes metal raised bed gardening an unpleasant experience. So it is crucial to have steel rust-resistant.
Basically, there are two approaches to stop steel parts from rusting :
1.Switch it to another metal that will not corrode when exposed to water.
2.Coat the steel with a physical barrier to prevent water from reacting with the iron.
Both of the approaches are primarily evaluated in terms of cost like most decisions in manufacturing industries.
Stainless Steel VS. Galvanized Steel
Occasionally switching from steel to another metal that does not rust such as stainless steel or aluminum is not a best bet simply because of the difference in cost: Economically a substitution doesn’t make sense. Aluminum is more expensive than steel, and stainless steel is a lot more expensive than aluminum. Moreover, steel might have certain physical characteristics, such as strength or weight that prohibits switching for a specific application. The next approach is to protect the steel with a physical barrier such as paint or a coating – this is what galvanizing does best.
How Galvanized Steel Resists Corrosion
Galvanizing is a zinc coating applied to sheets of steel through a process called “continuous hot-dip,” in which steel sheet passes through a bath of molten zinc. The liquid zinc bonds to the iron in the steel forming a protective layer on both sides of the sheet. The steel sheet can then be spun into a finished part because the zinc coating does not flake or peel off during the metal spinning process. The finished part resists corrosion without any additional or secondary painting or coating, making galvanized spinnings the most economical process for protecting steel from corrosion.
Hot dip galvanizing can and does provide long term rust protection for steel in some of the most harshest environments and is chosen as a corrosion protection system due to its inherent characteristics.
Barrier Protection and Steel Corrosion Protection
Barrier protection is the basic and most popular method of rust protection. It works by isolating the base steel from its surrounding environment. As long as the barrier is intact the steel is protected, however, if the barrier is breached corrosion will begin. Two important properties of hot dip galvanizing that enhance its barrier protection is its metallurgically bonded layers and the impervious nature of the coating. Steel also corrodes at approximately 10 to 36 times the rate of zinc depending upon the environment.
Steel corrosion protection, a continuous, impervious and tough – metallurgically bonded – coating completely covers steel, both internally and externally for hollow sections, that seals the steel from the environment, providing steel corrosion protection.
Sacrificial Protection and Rust Protection
Zinc also has the ability to galvanically protect steel. When bare steel is exposed to moisture, such as at a cut edge or damaged area, a galvanic cell is formed. The zinc around the point of damage corrodes in preference to the steel and forms corrosion products that precipitate on the steel surface and protect it. There is no sideways corrosion at points of damage.
The Zinc Patina Provides Corrosion Protection
Different from barrier and sacrificial protection, the zinc patina protects the zinc coating. The metallic zinc surface reacts with the atmosphere to form a compact, adherent patina that is insoluble in rainwater.
Galvanized steel progresses through a natural weathering process when exposed to wet and dry cycles in the environment. As galvanized coatings are exposed to the environment the formation of a thin zinc patina begins to form that consists of zinc oxides. This with further exposure to rain, dew and humidity reacts to form a layer of zinc hydroxide. During dry cycles, carbon dioxide reacts with the zinc hydroxide and forms a compact and highly adherent layer of zinc carbonate.
The rate of the patina formation varies according to the environmental conditions and can take approximately 6 – 12 months to develop. The fully developed patina is insoluble in rain or snow and is able to protect the galvanized coating underneath.
Galvanized steel is one that most commonly used in raised garden bed design. It is indeed able to prevent the steel or iron from rusting when it is in contact with moisture.
So what do you say about a raised garden bed made of 22-gauge 0.8mm thickness corrugated galvanized steel with multi-layer eco-friendly powder coatings?