Lead: Characteristics, Uses and Problems

Procedure code:
501014G
Source:
Division:
Metals
Section:
Metal Materials
Last Modified:
08/10/2016

References

  • Gayle, Margot, Look, David, and Waite, John. Metals in America's Historic Buildings: Uses and Preservation Treatments. Washington, DC: National Park Service, 1992.

  • Zahner, L. William. Architectural Metal Surfaces. New York: Wiley 2004.

Introduction

Characteristics of Lead

  • Very soft: without support, it can sag and become distorted.

  • Dense.

  • Durable.

  • Malleable.

  • Has a low melting point.

  • Long life-span (in milder climates, lead roofs have been known to last 200-300 years).

  • Generally corrosion-resistant - has little to no reaction with most compounds and solutions.

  • Resistant to corrosion by most acids including chromic, sulfuric, sulfurous and phosphoric acids.

  • Corrosive to alkalis (such as lime mortar, portland cement and uncured concrete), tannic acid found in wood, and radiation. Also corrosive to hydrochloric, hydrofluoric, acetic, formic and nitric acids.

NOTE: Ingestion of lead dust, typically through contact with older walls painted with lead paint, can result in serious long-term health problems, especially in the cases of young children or repeated exposure. See "Reducing Lead-Based Paint Hazards Using a Combination of Abatement and Interim Control Techniques on Windows" for more information and precautions associated with lead-based paint.

Typical Uses

Typical historical uses for lead included:
  • Lead Pipes: Sheets of lead were formed into tubes by bending and lead burning (welding).

  • Flashing, Gutters, Downspouts, and Conductor Heads: In roofing applications, lead was best used for flat or low pitch roofs and built-in gutters due to the heavy weight of the lead sheets. 

  • Prior to the late 17th century, lead was cast by hand in sand beds. Later, lead sheets were rolled in the mill and were, consequently, much lighter. Lead-coated copper was introduced in the 1930s. This consisted of sheet copper dipped first in a lead-tin alloy, then dipped in pure lead and then rolled.

  • Lead-based paint.

  • Red lead was typically used as a corrosion inhibitor for use on iron. 

  • White lead was used more frequently in commercial applications (white lead was not intended for use on iron - its use would increase corrosion, especially on wrought iron).

Typical current uses for lead include:
  • Sheet roofing.

  • Decorative spandrels.

  • Gutters, leader heads and downspouts.

  • Cast decorative features and sculpture.

  • Cupolas, spires and mullions.

  • Sheathing for cables.

  • Sheet lead partitions (good for noise reduction).

  • Pads for vibrating machinery.

  • Shielding for x-ray and nuclear radiation.

  • To waterproof ironwork where the iron is fitted into stone.

Natural or Inherent Problems

Chemical Corrosion

  • Lead has good corrosion resistance to the following acids: Chromic acid, sulfuric acid, sulfurous acid, and phosphoric acid.

  • Lead has poor corrosion resistance to: Alkalis like mortar and cement (evident as a reddish-brown oxide), carbon dioxide and organic acids like those found in wood (evident as a whitish carbonate coating).

  • Lead also has poor corrosion resistance to the following acids: Hydrochloric acid, hydrofluoric acid, acetic (i.e. fumes from breweries), formic acid (i.e. from ants and other insects), and nitric acid.

  • Lead is also susceptible to corrosion from tannic acid produced by oak, and acids from lichen on a roof that are washed over lead features such as flashing.

Galvanic (Electrochemical) Corrosion

  • Usually not a problem; lead is usually protected by a coating that forms on the surface and insulates the metal.

Mechanical or Physical Deterioration

  • Erosion and Abrasion: From dirt, sleet, hail and rain due to softness of metal.

  • Fatigue: Caused by thermal expansion and contraction

  • Buckling/Fatigue Cracking: May result from a high coefficient of thermal expansion.

  • Creep: Caused by the slow flow of gravity (usually a problem on steeper roofs). Creep and fatigue are often found together. One may accelerate the other.

END OF SECTION

 

Last Reviewed 2016-08-10