Lead paint

Lead paint or lead based paint (LBP) is paint containing lead, a heavy metal, that is used as pigment, with lead(II) chromate (PbCrO4, "chrome yellow") and lead(II) carbonate(PbCO3, "white lead") being the most common. Lead compounds were an important component of many historic paints. Lead, in the forms of lead carbonate and lead oxides, had excellent adhesion, drying, and covering abilities. White lead, linseed oil, and inorganic pigments were the basic components for paint in the 18th, 19th, and early 20th centuries.

Lead-based paint was used extensively on wooden exteriors and interior trimwork, window sash, window frames, baseboards, wainscoting, doors, frames, and high gloss wall surfaces such as those found in kitchens and bathrooms. Almost all painted metals were primed with red lead or painted with lead-based paints. Even milk (casein) and water-based paints (distemper and calcimines) could contain some lead, usually in the form of hiding agents or pigments. Varnishes sometimes contained lead. Lead compounds were also used as driers in paint and window glazing putty.

In 1978, the use of lead-based paint in residential housing was banned by the federal government. Because the hazards have been known for some time, many lead components of paint were replaced by titanium and other less toxic elements earlier in the 20th century. Since houses are periodically repainted, the most recent layer of paint will most likely not contain lead, but the older layers underneath probably will. Therefore, the only way to accurately determine the amount of lead present in older paint is to have it analyzed.

It is important that owners of historic properties be aware that layers of older paint can reveal a great deal about the history of a building and that paint chronology is often used to date alterations or to document decorative period colors. Highly significant decorative finishes, such as graining, marbleizing, stenciling, polychrome decoration, and murals should be evaluated by a painting conservator to develop the appropriate preservation treatment that will stabilize the paint and eliminate the need to remove it. If such finishes must be removed in the process of controlling lead hazards, then research, paint analysis, and documentation are advisable as a record for future research and treatment.

Lead Hazard Removal/Reduction
Rarely are there mandated requirements for the removal of lead-based paint from non-residential buildings. Ideally, most owners and managers should understand the health hazards created by lead-based paint and voluntarily control these hazards to protect young children. A stricter approach has been taken by some state and federal funding programs which have compliance requirements for identifying the problem, notifying tenants, and, in some cases, remedying lead hazards in housing. With new rules being written, and new products and approaches being developed, it is often difficult to find systematic and balanced methodologies for dealing with lead-based paint in historic properties.

Typical health department guidelines call for removing as much of the surfaces that contain lead-based paint as possible. This results in extensive loss or modification of architectural features and finishes and is not appropriate for most historic properties. A preferred approach, consistent with the tenets of historic preservation, calls for removing, controlling, or managing the hazards rather than wholesale-or even partial-removal of the historic features and finishes. This is generally achieved through careful cleaning and treatment of deteriorating paint, friction surfaces, surfaces accessible to young children, and lead in soil. Lead-based paint that it not causing a hazard is thus permitted to remain, and, in consequence, the amount of historic finishes, features and trimwork removed from a property is minimized.

Long-term abatement solutions include permanent removal of hazardous paint through chemicals, heat guns or controlled sanding/abrasive methods; permanent removal of deteriorated painted features through replacement; the removal or permanent covering of contaminated soil; and the use of enclosures (such as drywall) to isolate painted surfaces. The use of specialized elastomeric encapsulant paints and coatings can be considered as permanent containment of lead-based paint if they receive a 20-year manufacturer's warranty or are approved by a certified risk assessor. Within the context of the historic preservation, the most appropriate method will always be the least invasive.

Lead levels in paint
Lead in paint: Differing methods report results in differing units. Lead is considered a potential hazard if above the following levels, but can be a hazard at lower levels, if improperly handled. These are the current numbers as identified by the Department of Housing and Urban Development (1995):

Lab analysis of samples:
 * 5,000 milligram per kilogram (mg/kg) or 5,000 parts per million (ppm), or
 * 0.5% lead by weight.

XRF reading: in milligram per centimeter squared
 * 1 mg/cm2

Lead dust wipe test: in micrograms per square foot
 * Floors 100 ug/ft2;
 * Window sills 500 ug/ft2;
 * Window troughs 800 ug/ft2

Lead in soil: high contact bare play areas, listed as parts per million (ppm)
 * concern: 400 ppm
 * interim control 2,000 ppm
 * hazard abatement 5,000 ppm