As we marvel at the intricate restoration work being done on the Notre Dame Cathedral, it’s essential to understand the materials involved in such monumental projects. The Notre Dame’s lead roof and ornamental cresting have long been iconic features, but there are some critical factors to consider regarding the use of lead in these applications.
While lead is stable and has been historically favored for its workability and durability, it also poses significant challenges in the environment. Even though lead is relatively low on the reactivity scale—surpassing even tin, which we adore for its stability and usefulness in various applications—it behaves differently when exposed to environmental conditions.
Why Lead Thins Quickly in the Environment
Despite its stability under controlled conditions, lead corrodes and thins more rapidly when exposed to water, especially acidic or soft water. This environmental exposure leads to the formation of soluble lead compounds that wash away, gradually reducing the thickness of the lead material. Over time, this can significantly compromise the integrity and longevity of structures like the Notre Dame’s roof and cresting.
Kölner Dom (Cologne Cathedral): A Case in Point
Take the Kölner Dom (Cologne Cathedral) as an example. This magnificent structure is almost always under repair, mostly due to the materials originally used in its construction. Remember, these are German craftsmen who are REALLY good at this. Only the best of the best are invited to do these kinds of projects. It’s not the technique that’s failing this building. The frequent maintenance that is required to address the wear and tear comes from the environmental exposure. This shows the clear need for more durable and sustainable materials. We appreciate the sentiment of preserving historical materials, but…when you know better, you do better.
Toxicity Concerns
Another crucial consideration is the toxicity of lead. Lead runoff from roofs can contaminate water sources, posing serious health risks to both humans and wildlife. This makes the use of lead particularly concerning in today’s environmentally conscious construction and restoration practices.
Historical Recognition of Lead Toxicity
Lead has been known to be toxic for centuries, but it became more universally recognized and addressed as a public health issue in the mid-20th century. Significant awareness and regulatory action regarding the toxicity of lead occurred in the following decades:
- 1920s: The dangers of lead poisoning began to be more widely recognized, particularly in industrial settings. Lead paint and leaded gasoline were identified as major sources of exposure.
- 1940s and 1950s: Studies increasingly linked lead exposure to serious health problems, particularly in children. Lead poisoning became a recognized medical condition.
- 1960s: Public health campaigns and research highlighted the widespread issue of lead poisoning, especially in urban areas with older housing stock where lead paint was prevalent.
- 1970s: Regulatory measures began to be implemented. In the United States, the Clean Air Act of 1970 led to the phasing out of leaded gasoline, and the Consumer Product Safety Commission banned lead paint in 1978.
The 1960s and 1970s were the pivotal decades when lead’s toxicity became universally acknowledged and significant regulatory actions were taken to mitigate its use and reduce exposure.
Alternatives: Terne and Zinc
Looking at alternatives, we find that materials like terne-coated stainless steel or zinc offer compelling advantages:
- Zinc: Zinc forms a stable, self-repairing protective layer that resists corrosion much better than lead. This makes it an excellent choice for roofing and ornamental elements that must withstand the elements over long periods. Its lower reactivity and environmentally friendly profile make it a preferable option.
- Terne-Coated Stainless Steel: Terne, traditionally a lead-tin alloy, has evolved. Modern terne coatings are often lead-free, combining tin with stainless steel for enhanced durability and corrosion resistance. This material offers a similar aesthetic to lead but without the associated environmental and health risks.
Our Expertise in Restoration
At Spengler Industries, we are board certified in restoration and reconstruction, ensuring that our work meets the highest standards of craftsmanship and sustainability. We create beautiful crestings like those seen on Notre Dame, using materials that stand the test of time and respect our environmental responsibilities.
For more insights into the benefits and applications of alternative materials, check out our previous article on lead-coated copper here.
In that article, we discussed the reactivity of various metals, noting that lead is relatively stable in controlled conditions and even less reactive than tin. However, we didn’t sufficiently clarify the difference between reactivity and environmental performance. To reiterate points already made for sake of clarity, reactivity refers to how easily a metal undergoes chemical reactions under controlled conditions, while environmental performance considers how a metal behaves when exposed to real-world conditions like water and atmospheric pollutants. Although lead is less reactive, it can still corrode and thin quickly in the environment, making it less suitable for long-term applications compared to zinc or modern terne-coated materials.
Distinguishing Reactivity from Environmental Behavior
It’s crucial to distinguish between the inherent reactivity of a metal and how it behaves in the environment. Lead’s low reactivity makes it stable under controlled conditions, but when exposed to water and atmospheric pollutants, it corrodes and sheds, thinning over time. This contrasts with metals like zinc and modern terne, which maintain their integrity better under similar conditions.
At Spengler Industries, we are committed to providing sustainable, long-lasting solutions for your architectural restoration needs. Our expertise in using durable materials like zinc and modern, but historically appropriate terne ensures that your projects stand the test of time, both in beauty and functionality. Contact us today to learn more about our restoration services and how we can help preserve the legacy of your structures with our board-certified craftsmanship. Visit our website or reach out to us directly to discuss your next project.
