Aluminum is a widely used material in construction due to its strength and lightweight nature.
However, when aluminum comes into contact with materials like concrete or steel, it’s important to take certain precautions to maintain its integrity.
Without proper protection, aluminum can be susceptible to corrosion and other forms of damage.
This article focuses on best practices for dealing with aluminum in contact with concrete and dissimilar metals.
This article explores effective solutions for preventing corrosion, including the use of protective coatings and proper material separation to ensure aluminum’s long-term durability.
Why Aluminum Shouldn’t Be in Direct Contact with Concrete or Dissimilar Metals
Aluminum should not be in direct contact with concrete or dissimilar metals due to the risk of corrosion.
When aluminum comes into contact with concrete, a chemical reaction can occur, leading the aluminum to weaken and deteriorate. This is especially true if the concrete is wet, as moisture can accelerate the process.
Similarly, when aluminum is in contact with other metals like steel, galvanic corrosion can happen. This occurs when two different metals are in contact and exposed to an electrolyte, causing one of the metals to corrode more quickly.
To prevent these issues, it’s essential to use proper separation materials or coatings to protect the aluminum from direct contact with concrete or dissimilar metals.
Protecting Aluminum with Paint or Coatings
The ADM (Aluminum Design Manual) emphasizes the importance of protecting aluminum from concrete and dissimilar materials, particularly through the use of paint or coatings.
They create a durable barrier between the aluminum surface and potential corrosive elements like moisture, chemicals, or other reactive metals. By applying a protective paint or coating, the surface of the aluminum is sealed off, preventing direct contact with harmful substances. This is particularly important for situations where aluminum is exposed to water, chemicals, or metals that can cause galvanic corrosion.
“Aluminum surfaces shall be painted if they are to be placed in contact with concrete or masonry unless the concrete or masonry remains dry after curing and no corrosive additives such as chlorides are used.”
2020 ADM Chapter M – Section M.7.3
“Where 1) aluminum contacts other metals except 300 series stainless steel, zinc, or cadmium and 2) the faying surfaces are exposed to moisture, the other metal shall be painted or coated with zinc, cadmium, or aluminum. Uncoated aluminum shall not be exposed to moisture or runoff that has come in contact with other uncoated metals except 300 series stainless steel, zinc, or cadmium.”
2020 ADM Chapter M – Section M.7.1
Powder Coating: A Strong Defense Against Corrosion
Powder coating is an effective way to protect aluminum from corrosion by creating a tough, durable barrier between the metal and its environment.
Unlike liquid paint, which can result in uneven coverage or require multiple layers, powder coating uses a dry powder made of polyester, epoxy, or acrylic. The powder is electrostatically applied to the aluminum surface and then heat cured, forming a strong, protective layer. This process forms a thick, uniform layer that adheres tightly to the metal, offering better edge coverage and minimizing weak points where corrosion could start.
Compared to traditional paint, powder coating is less likely to chip, peel, or crack over time, thanks to its strong bond with the surface. It also resists UV rays, moisture, and chemicals more effectively, providing long-lasting protection.
Additionally, powder coatings don’t require solvents or emit volatile organic compounds (VOCs), making them an eco-friendlier option.
With a wide range of colors and finishes available, powder coating not only preserves the aluminum’s structural integrity but also enhances its appearance, making it a practical and durable choice for construction and architectural applications.
Protecting Aluminum with Proper Separation Methods and Materials
Another good method is separation, which is emphasized in the ASD (Aluminum Design Manual). This solution is particularly useful when it’s difficult to apply coatings or paints, or when additional protection is needed in high-risk areas.
“As an alternative to the requirements of Sections M.7.1 through M.7.3, aluminum shall be separated from the materials of this Section by a nonporous isolator compatible with the aluminum and the dissimilar material.”
2020 ADM Chapter M – Section M.7
Separation can be done using different methods, such as using nonporous isolators, spacers, or gaskets. These materials create a barrier between aluminum and other metals or concrete, preventing direct contact and reducing the risk of corrosion.
- – Nonporous Isolators: Typically plastic or polymer sheets acting as a solid barrier between aluminum and concrete or dissimilar metals.
- – Spacers: Materials like rubber, neoprene, and butyl are commonly used as spacers to create a physical gap between aluminum and other surfaces. They are flexible, durable, and easy to install, making them suitable for a variety of applications.
- – Gaskets: Usually made from materials like EPDM, neoprene, or butyl rubber. Gaskets are often used in joints, fastener points, and areas where aluminum meets concrete or steel, providing both separation and weatherproofing.
Corrosion Risks with Screw Anchors
Corrosion doesn’t just affect visible metal surfaces, it also threatens screws and anchors, making it crucial to carefully select fasteners for aluminum connections.
ASD Section M.7.1 emphasizes this risk, especially for high-strength steel fasteners, noting that fasteners with a tensile strength greater than 120 ksi should not be used with aluminum because their high strength are more likely to lead to galvanic corrosion and hydrogen-assisted stress corrosion cracking, compared to regular steel fasteners.
“Steel fasteners with a specified minimum tensile ultimate strength greater than 120 ksi in the load bearing portion of the shank shall not be used in contact with aluminum.”
2020 ADM Chapter M – Section M.7.1
Corrosion weakens the anchors by slowly eating away at the metal, reducing their load-bearing capacity and compromising the stability of the entire connection.
To prevent fasteners from corrosion, it’s essential to choose the right materials and protective measures. Here are some common solutions:
- – Stainless Steel: Contains chromium, which forms a protective layer (chromium oxide) that prevents rust. It is highly durable and ideal for harsh environments where long-term corrosion resistance is needed.
- – Galvanized Steel: Coated with zinc, which corrodes before the steel does, protecting it from rust. It is more cost-effective than stainless steel but offers less corrosion resistance.
- -Paint/Coating : As mentioned earlier, protective coatings are also applicable to fasteners.
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Last Update: March 17, 2025
