Pitch tar is a thick, black, sticky substance produced by heating organic materials like coal, wood, or petroleum at high temperatures without air. It has been used for thousands of years as a waterproofing agent and adhesive, and it remains an important industrial material today. The term “pitch tar” is often used loosely to refer to either tar itself or its heavier residue called pitch, though technically the two are distinct stages of the same product.
How Tar and Pitch Relate
Tar is the broader category. It forms as a condensate during a process called destructive distillation, where organic materials are heated in an enclosed space without oxygen. Coal tar, wood tar, and petroleum tar are the most common types. When tar is further distilled and its lighter oils are boiled off, the heavy residue left behind is pitch. So pitch is essentially concentrated tar, thicker and with a higher softening point.
A typical batch of coal tar from a coke oven contains about 72% pitch by weight, with the remaining 28% made up of heavy, medium, and light oils plus trace moisture. The chemical makeup of coal tar pitch is roughly 75% carbon, 8% hydrogen, and 16% oxygen, with small amounts of nitrogen and sulfur. These numbers shift depending on the source material and processing temperature, but the result is always a dense, hydrocarbon-rich substance loaded with compounds called polycyclic aromatic hydrocarbons (PAHs).
How Pitch Tar Is Made
The production process starts with heating the source material (usually coal) inside sealed ovens or retorts. As temperatures climb, volatile gases and liquids are driven off and collected. The liquid condensate is crude tar. To separate pitch from this crude tar, manufacturers use fractional distillation: the tar is gradually heated through a range of about 100°C to 450°C under reduced pressure. As the temperature rises, lighter fractions boil off first, leaving progressively heavier material behind. Once the flask reaches around 250°C, the remaining substance is poured off as pitch.
Wood tar follows a similar principle but starts with resinous woods like pine instead of coal. Wood tar contains creosote, which gives it strong preservative properties. This is the type historically used to protect wooden structures and ships.
Physical Properties
At room temperature, pitch can range from a brittle solid to a thick, slow-flowing liquid depending on its grade. Industrial coal tar pitch is classified by its softening point, which typically falls between 95°C and 120°C for standard binder grades. Below its softening point, pitch behaves like a solid. It can even shatter if struck. But given enough time and warmth, it flows, a property famously demonstrated by the University of Queensland’s pitch drop experiment, where a single drop of pitch takes roughly a decade to fall.
This dual nature, solid enough to hold shape but capable of flowing under heat and pressure, is what makes pitch so useful as an industrial binder and sealant.
Historical Uses in Shipbuilding
Pitch tar was one of the most strategically important materials in the premodern world. Shipbuilders used it to waterproof hulls, seal the gaps between planks (a process called caulking), and protect rigging and ropes from saltwater rot. Archaeological analysis of medieval shipwrecks, including 11th and 15th century vessels excavated from Roskilde harbour in Denmark, has confirmed the widespread use of tarry caulking compounds in northern European shipbuilding.
By the medieval period, control over pitch and tar production had become a matter of political and military significance for European seafaring nations. Scandinavia and the Baltic regions were major suppliers, and access to these materials directly influenced naval power. The British Royal Navy consumed enormous quantities, which partly drove colonial interest in North American pine forests.
Modern Industrial Uses
Today, coal tar pitch serves as a critical binder in aluminum manufacturing. Carbon anodes, the electrodes used in aluminum smelting, are held together with coal tar pitch. The pitch gives the carbon mix its consistency and allows it to be shaped through extrusion or molding before being baked into solid form.
Pitch also shows up in roofing and pavement maintenance. Coal tar-based sealants used on driveways, parking lots, and playgrounds can contain as much as 35% coal tar pitch. These sealants protect paved surfaces from water and UV damage. However, because of health concerns tied to their PAH content, some U.S. states have restricted or banned coal tar sealants for non-roofing applications. Illinois, for example, defines any sealant with more than 0.1% PAH content by weight as a regulated coal tar product.
Medical Uses for Skin Conditions
Coal tar has a long history in dermatology, particularly for treating psoriasis and eczema. Crude coal tar contains thousands of individual compounds, many still unidentified. The therapeutic effect is thought to come primarily from its polycyclic aromatic hydrocarbons, with one compound called carbazole receiving the most research attention. Carbazole appears to activate a receptor in skin cells that helps slow the rapid cell turnover characteristic of psoriasis.
Coal tar treatments are available over the counter in shampoos, creams, and ointments at low concentrations. They reduce scaling, itching, and inflammation, though the exact mechanism is still not fully mapped out.
Health Risks and Exposure Limits
While low-concentration coal tar products are considered safe for skin treatment, occupational exposure to coal tar pitch volatiles is a serious health concern. The International Agency for Research on Cancer classifies coal tar pitches as Group 1 carcinogens, meaning there is sufficient evidence that they cause cancer in humans. The U.S. National Toxicology Program also lists coal tars and coal tar pitches as known human carcinogens.
The primary danger comes from inhaling or absorbing PAHs released when pitch is heated or disturbed. Workers in aluminum smelting, roofing, road paving, and coke production face the highest exposure. OSHA sets the permissible exposure limit for coal tar pitch volatiles at 0.2 milligrams per cubic meter of air over an eight-hour workday. Skin contact is also a concern, as PAHs can be absorbed through the skin and cause irritation, burns, and increased sensitivity to sunlight.
For the general public, the most common source of low-level exposure is from coal tar-based pavement sealants, which release PAHs into surrounding soil and waterways as they wear down over time. This environmental runoff is the main reason several jurisdictions have moved to restrict their use.