ALUMINUM IN COLUMBARIUM APPLICATIONS
Columbarium Engineering Basics Series by Architarium

Architarium sometimes receives questions about aluminum, especially in comparison to stainless steel. More recently, questions have been posed about anodized aluminum. We are in a good position to respond, having degreed engineers on staff and having worked with a wide range of materials.  In fact, Architarium made a deliberate and expensive transition from aluminum to stainless steel. Aluminum is frequently used in construction due to its somewhat lighter weight and somewhat more affordable cost (both to purchase and to manufacture). But how does it perform?

Aluminum is a very chemically reactive metal which creates a propensity to corrode.  It will corrode with the presence of air and moisture (aka. passivation). The oxidization actually can provide some protection against further corrosion. In fact, oxidization can be artificially induced to create anodized aluminum. Regardless, an oxidization layer provides corrosion resistance, not corrosion proofing. This is true even for marine aluminum (alloy series 5000 and 6000). Any oxidized coating, natural or anodized, can fail from pitting, cracking, flaking, abrasion, etc. Failure of this seal exposes the aluminum to all kinds and degrees of corrosion. Flaking, or exfoliation, also involves a loss of material.

In addition, most types of chemical corrosion that aluminum experiences are not beneficial. Caustic elements in the environment such as everyday chemicals or acid rain can adversely affect aluminum. Aluminum is particularly vulnerable to aqueous salts. Being highly reactive, aluminum can experience several types of electrical corrosion: 1) galvanic corrosion (dissimilar metals like aluminum and steel or brass urns) and 2) electrolytic corrosion (dissimilar materials like aluminum and granite face plates). Elements like niche floor pads or niche door powder coating may be evidence of efforts to mitigate the potential for such corrosion.

As a result of aluminum’s propensity to corrode, even when anodized, aluminum applications may have an industrial coating. In fact, coating has even been recommended on anodized aluminum. Liquid polyurethane can protect aluminum but may separate due to a weak bond. Instead, more sophisticated industrial coatings like powder coating or enamel are better. However, these coatings must be applied to all aluminum in the product and will significantly add to the final cost. And like anodization, powder coat and enamel can fail.

Aluminum is very susceptible to corrosion, but what about its strength? Per cubic inch, aluminum is not as strong as many other metals like stainless steel. It must be much thicker to compete. Regardless of thickness, aluminum alloys will differ in specific material strengths, like compression, yield, tensile, impact, etc. So it would be misleading to imply that thicker metal is stronger. In fact aluminum has a specific strength issue because all aluminum alloys lack fatigue strength, meaning that they will eventually wear out from stress. (Google “aluminum fatigue limit” or “aluminum endurance limit”). An aluminum structure can experience many stresses, such as capstone loads, high winds, mechanical attachment operation, etc. Aluminum can also experience stress due to its own expansion and contraction. It has a high coefficient of expansion. When in contact with materials with dissimilar coefficients of expansion, such as aluminum and masonry or granite, stress from thermal expansion and contraction can damage both materials.

Construction methods for aluminum can greatly affect both the corrosion resistance and strength of the final structure. For example, if aluminum parts are cut from anodized sheets as opposed to being anodized after cutting, the part edges will be exposed to corrosion. It may be possible to use pre-anodized flat panels. At least the possibility of stress cracks from bending would be eliminated. But flat panels introduce joints which have potential issues: structural weakness, multiple types of corrosion and lack of moisture prevention. Welding could eliminate these issues but aluminum is quite difficult to weld correctly compared to other metals. The welding challenge also makes aluminum more difficult to repair, especially retaining its original strength.

Architarium started manufacturing with powder-coated aluminum, bypassing anodized aluminum, but eventually concluded that it was important to convert to stainless steel to maximize quality. We did this knowing that stainless steel is more expensive to purchase and fabricate than aluminum. The higher price of stainless steel compared to aluminum is an indication of its value. Stainless steel is far less reactive than aluminum, is inherently more corrosion resistant internally and externally than aluminum, has a much lower coefficient of expansion than aluminum, is stronger than aluminum per square inch and allows better structural integrity than aluminum. As engineers, we concluded that stainless steel is the best metal for columbarium durability in the widest range of conditions.

For detailed information on the material qualities of aluminum (and stainless steel), please read Architarium’s materials guide: Columbarium Materials Comparison.