Tar is made by slowly heating wood in a low-oxygen environment, a process called pyrolysis. The wood breaks down without fully burning, releasing gases that condense into a thick, dark liquid. The type of wood you start with determines the type of tar you get, and the temperature and timing of the process control the quality of the final product.
Wood Tar vs. Coal Tar
These two substances share a name but are chemically very different. Wood tar, made from trees like pine or birch, is rich in phenols, cresols, and guaiacols. These compounds give wood tar its antiseptic properties and its distinctive smoky smell. Coal tar, by contrast, is a byproduct of processing coal at high temperatures. At least 75% of coal tar consists of polycyclic aromatic hydrocarbons (PAHs), a class of compounds linked to increased cancer risk with prolonged exposure. Wood tar contains far fewer PAHs, which is why it has a much longer history of safe topical and practical use.
When most people talk about “making tar,” they mean wood tar, specifically pine tar or birch tar. Coal tar is an industrial byproduct that requires coking ovens and isn’t something you’d produce at home.
Choosing Your Wood
Pine and birch are the two most common sources. Pine tar comes from the resinous heartwood and roots of pine trees. The natural resins in pine, which contain compounds called diterpenoids, produce a tar that’s sticky, waterproof, and mildly antiseptic. It has been used for centuries to seal boats, preserve rope, and treat skin conditions.
Birch tar comes from birch bark and has a different chemical profile. It was the adhesive of choice in prehistoric Europe. Archaeologists have found birch tar on stone tools dating back tens of thousands of years, used to glue flint blades to wooden handles. Birch tar tends to be harder when cool and was historically valued more as a glue than a sealant.
For a first attempt, pine is easier to work with. Fatwood (the resin-saturated heartwood found in old pine stumps) produces the highest yield because it’s already loaded with flammable resins.
The Basic Pit Method
The simplest traditional method uses two containers and a fire. You need a metal can or clay pot with a small hole in the bottom, a collection container buried below it, and a heat source around the upper container.
Start by filling the upper container tightly with small pieces of your chosen wood or bark. Pack them as densely as possible to limit the amount of oxygen inside. Seal the top with a lid, clay, or mud, leaving only the small hole at the bottom open. This hole allows the liquid tar to drip down into the collection vessel below.
Dig a small hole in the ground and place your collection container (a tin can or jar) inside it. Position the packed upper container directly over the hole so the drip point lines up with the collector. Then build a fire around and on top of the upper container. The goal is to heat the wood to roughly 300 to 400 degrees Celsius without letting it catch fire. This slow baking drives out the volatile compounds, which condense and drip down as raw tar.
The process takes several hours depending on the size of your setup. A small tin-can version might run for 3 to 4 hours. You’ll know it’s working when you see dark liquid collecting below and smell the sharp, smoky odor of wood gases.
The Double-Container Method
A more controlled approach uses two stacked metal containers, like paint cans or large food tins. Punch several small holes in the bottom of the upper can. Fill it with tightly packed wood, then invert it over the lower (empty) collection can. Seal the seam between them with clay or mud to keep oxygen out.
Bury the lower can partway in the ground to keep it cooler, which helps the tar condense. Build your fire around and over the upper can only. The heat breaks down the wood above, and the resulting gases travel downward through the holes, cooling as they enter the lower container and condensing into liquid tar.
This method gives you better separation between the tar and the wood remnants (which become charcoal in the upper can). You’ll also end up with usable charcoal as a byproduct.
Separating Tar From Wood Vinegar
Raw tar collected from pyrolysis is actually a mixture. It contains true tar (the thick, dark, resinous liquid you want), wood vinegar (a watery, acidic liquid also called pyroligneous acid), and sometimes a heavier residue called pitch.
These separate naturally based on temperature. In industrial settings, the pyrolysis gases first pass through a high-temperature condenser set above 80°C, where the tar condenses out as a liquid while the lighter wood vinegar remains as gas. The vinegar then condenses at a much lower temperature, below 20°C. At home, you won’t have this level of control, but you can still separate the two after collection.
Let your raw collection sit undisturbed for a day or two. The tar, being heavier and more viscous, sinks to the bottom. The wood vinegar, which is thinner and lighter in color, floats on top. You can carefully pour or siphon off the vinegar layer. The wood vinegar itself is useful as a garden pest deterrent and soil amendment, so don’t discard it.
Refining and Thickening
Fresh tar is often thinner than you’d expect. To thicken it into a more usable consistency, gently reheat it in an open container over low heat. This evaporates remaining water and light volatile compounds, leaving behind a thicker, stickier product. Keep the temperature low and stir frequently. If you overheat tar, it can ignite, so patience matters here.
If you continue heating tar past the point of thickening, you eventually drive off nearly all the volatile compounds and produce pitch: a brittle, glass-like solid at room temperature that becomes moldable when warm. Pitch was the primary waterproofing material for wooden ships for centuries.
Common Uses for Wood Tar
Pine tar has been used in medicine for over 2,000 years, first described by Hippocrates in ancient Greece. Commercial pine tar products are available over the counter in many countries and are used to relieve itching and inflammation from eczema, psoriasis, seborrheic dermatitis, and insect bites. Products sold in Australia, for example, contain up to 2.3% pine tar in formulations safe for use on the entire body, including the face. The FDA classifies coal tar (at regulated concentrations) as safe and effective for treating dandruff, seborrhea, and psoriasis, though wood tar and coal tar products are not interchangeable.
In veterinary medicine, pine tar is a traditional antiseptic and hoof care product for horses and cattle. Poultry farmers apply it to chickens to discourage pecking injuries. For outdoor and woodworking applications, pine tar mixed with linseed oil creates a traditional finish for wooden boats, fences, and log cabins that repels water and resists decay.
Safety During Production
The biggest risk when making tar is fire. You’re heating flammable materials surrounded by an open fire, and the gases produced are themselves combustible. Work outdoors on bare ground, away from structures, dry grass, and overhanging branches. Keep water or a fire extinguisher nearby.
The smoke and fumes produced during pyrolysis contain PAHs, which are harmful with repeated or prolonged exposure. The National Institute for Occupational Safety and Health has concluded that long-term occupational exposure to coal products, including their tars and pitches, increases the risk of lung and skin cancer. Wood tar produces fewer PAHs than coal tar, but the smoke is still irritating and worth avoiding. Work upwind, and don’t lean over the setup to check progress. If you make tar regularly rather than as a one-time project, wearing a respirator rated for organic vapors is a reasonable precaution.
Skin contact with raw tar can cause irritation in some people. Wear gloves when handling the finished product, and keep it off your skin until it’s been diluted or refined for its intended purpose.