Historic sheet metal restoration · Lesson 2 of 4

Historic sheet metal restoration: materials, standards and design constraints

What the Guidelines and Preservation Briefs say about cleaning, painting, mixed metals and substitutes for terne; the Texas landmark review; historic sheet sizes against AFS pieces; copper weights; and the OSHA and EPA lead rules.

You will be able to: Apply the federal Guidelines, the substitute-material tests and the Texas review path to a sheet metal restoration, avoid mixed-metal and coating mistakes, relate historic sheet sizes and copper weights to AFS pieces, and apply the OSHA and EPA lead rules correctly.

12 min · 12 slides · 9 questions

All lessons in this module

Slide 1 of 12

Identify the metal, then clean gently

Before any cleaning, identify the particular type of metal, then pick the gentlest method that works.

For soft metals such as lead, tinplate, terneplate, copper and zinc, the Guidelines recommend non-corrosive chemical methods and warn against abrasive methods such as sandblasting.

These are the recommendations in the Preservation treatment of the 2017 Guidelines.

Sources

The Secretary of the Interior's Standards for the Treatment of Historic Properties with Guidelines, 2017 (Part 1: Preservation and Rehabilitation; Metals and Roofs sections, Preservation treatment) - U.S. National Park Service, Technical Preservation Services

Videos for this lesson

What this video shows: The Copper Development Association shows how to make a flat seam soldered joint on slopes up to 3:12, including the preparation and tools. It shows soldered copper work, so it illustrates the technique only; it is not a safe-work procedure for a historic roof.

Video: How-To: Flat Seam Soldered Joint by Copper Development Association, on YouTube. Chosen from the video's published description.

Glossary

Galvanic corrosion: Corrosion that occurs when unlike metals touch in the presence of moisture; the Guidelines note that copper will corrode cast iron, steel, tin and aluminum, so unlike metals need a separation material.
Patina: The surface film that forms on some metals, such as copper and bronze; the Guidelines say it may be both a protective layer and a distinctive finish, so it is not removed.
Action level and permissible exposure limit: OSHA's construction lead standard sets an action level of 30 and a permissible exposure limit of 50 micrograms of lead per cubic meter of air, each as an 8-hour time-weighted average.
Recorded Texas Historic Landmark: A Texas designation for which the owner must notify the Texas Historical Commission in writing at least 60 days before work that changes its historical or architectural integrity, which includes exterior work.