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We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
This standard includes general information on the characteristics and common uses of tin and identifies typical problems associated with this material along with common causes of its deterioration.
Introduction
Characteristics of Tin:
- Silvery-white metal
- Non-magnetic
- Fairly resistant to corrosion
- Non-combustible
- Lightweight
- Durable
- Soft
- Ductile
- Malleable
- Expensive, but can last long time when properly maintained
- Low maintenance material consisting primarily of routine inspection and periodic painting.
Tin is typically used in alloying with other metals (i.e. alloying tin with copper to form bronze). It is also used to coat harder metals such as iron and steel. Before the 20th century, sheets of iron and steel were hand-dipped in molten tin or a combination of tin and lead to make tin- and terneplate. In the 20th century, electroplating, or the process of coating a base metal with tin using an electric current, became popular.
- Tinplate: Sheet iron or steel which has been coated with pure tin. The tin offers a light weight, corrosion resistant finish highly suitable for a roofing (and walling) material.
- Terneplate: Sheet iron or steel which has been coated with a mixture of lead (75-90%) and tin (10-25%). The addition of the lead provides more durability.
- These materials must be painted. For roofing, both the surface and the underside of the material should be painted. They are typically painted a red or reddish-brown color or green to simulate copper. When properly maintained, tin- and terneplate roofing can last 50-100 years.
Typical Uses
Typical historical uses for pure tin included:
- Lighting devices such as perforated lanterns,
- Candle shields,
- Wall sconces, and
- Mirror frames.
Typical historical uses for tinplate and terneplate included:
- Roofing material: Sheets of terne- and tinplate were soldered and/or mechanically fastened together to form a continuous waterproof covering.
- Decorative machine-pressed shingles: These began to be manufactured in the late 19th century to simulate tile roofs.
- Sheet metal wall covering formed to imitate masonry or other building materials.
- Flashing, gutters and downspouts
- Dormers
- Fire protection on wood doors and shutters
- Ornamental elements such as door and window heads, balusters and urns, or roof ornaments
Natural or Inherent Problems
- Chemical Corrosion:
- Tinplated coatings generally have good corrosion resistance to: Oxygen, moisture, sulfur dioxide and hydrogen sulfide.
- Tin- and terneplated coatings generally have poor corrosion resistance to: Asphaltic and bituminous roofing materials such as building paper and roofing cement, and paints containing either asphalt or bitumen, acids, graphite or aluminum.
- Galvanic corrosion will occur, causing tin- or terneplate to corrode, if these metals come in contact with copper.
- Tin- and terneplate will cause aluminum and bare iron or steel to corrode.
- Mixing metals used for flashing, gutters and downspouts, decorative elements, windows or roof covering will also cause galvanic corrosion.
Vandalism Or Human-Induced Problems
Mechanical or physical deterioration:
- Tin- and terneplate are resistant to corrosion as long as the tin or terne coating is not damaged. If, however, the coating becomes damaged by falling objects, such as tree limbs or heavy roofing materials for instance, the base metal may become exposed and begin to corrode. Galvanic action between the tin and the iron or steel will also accelerate the deterioration.
Tin- or terneplate roofing may be suitably replaced with lead-coated copper or terne-coated stainless steel. The initial cost for either of these materials is higher, but more durable and easier to maintain.
References:
Zahmer, L. William. Architectural Metals. New York: John Wiley & Sons, 1995.
Gayle, M., Look, D. Waite, J. Metals in America’s Historic Buildings. Washington: National Park Service, 1992.