Wood Tar Production

Part of Petroleum and Tar

Producing tar from wood through destructive distillation — selecting wood, preparing materials, and running the process from start to finish.

Why This Matters

Wood tar is the most accessible petroleum-substitute a rebuilding community can produce. Unlike crude oil, which requires specific geological formations and extraction infrastructure, wood tar can be made anywhere trees grow. It requires no specialized equipment beyond a fire and an enclosed container. Every forested civilization in history — from Neolithic boat builders to Viking shipwrights to American frontier settlers — produced wood tar as an essential material.

The applications are immediate and critical. Tar waterproofs boats, roofs, ropes, and containers. It preserves timber from rot and insect damage, extending the useful life of structural wood by decades. Mixed with animal fat, it becomes a superior axle lubricant. Diluted with turpentine (itself a tar byproduct), it creates wood stain and paint. Heated and mixed with fibers, it becomes a powerful adhesive. Tar-soaked rope becomes waterproof caulking for sealing joints in boats, barrels, and cisterns.

Beyond direct use, wood tar production teaches the fundamental chemistry of destructive distillation — heating organic material in the absence of air to decompose it into useful fractions. This same principle applies to producing charcoal, coal gas, coke, and eventually more sophisticated chemical processes. Mastering wood tar production is a gateway skill for an entire branch of applied chemistry.

Wood Selection and Preparation

Best Species for Tar

Not all wood produces tar equally. Resinous softwoods yield the most tar per unit of wood:

Species	Tar Yield (% of dry weight)	Quality	Notes
Pine (heartwood)	15-25%	Excellent — thick, durable	Best overall choice; old-growth stumps are ideal
Spruce	10-15%	Good	Common, easy to process
Fir	8-12%	Good	Less resinous than pine
Larch	12-18%	Very good	Especially resinous heartwood
Birch (bark)	20-30% (from bark only)	Excellent — different character	Birch bark tar is thinner, used as adhesive
Juniper	10-15%	Good	Strong antiseptic properties
Hardwoods	3-8%	Poor for tar	Produce more wood vinegar instead

Fat Pine

The richest tar source is “fat pine” or “lightwood” — the resin-saturated heartwood of dead pine trees, especially old stumps that have stood for years after the tree died. The sapwood rots away while resin concentrates in the heartwood. A single fat pine stump can yield more tar than a whole green pine tree.

Harvesting and Preparation

For pine and softwoods:

1. Select dead standing trees — they have lower moisture content and often higher resin concentration
2. Fell and buck — cut into manageable lengths (50-80 cm)
3. Split into billets — split each round into pieces roughly 5-8 cm across. Smaller pieces produce tar faster because heat penetrates more quickly.
4. Remove bark — bark can be processed separately or included, but removing it gives cleaner tar
5. Air-dry — stack split billets in a covered area with good airflow for 2-4 weeks. Dry wood produces more tar because less energy is wasted evaporating water.

For birch bark:

1. Harvest bark — peel bark from dead or recently felled birch trees. Never strip bark from living trees in a ring (it kills them).
2. Roll tightly — roll bark sheets into tight cylinders and secure with cord
3. Dry — birch bark dries quickly; 1-2 weeks is sufficient

Quantity Planning

Estimate your wood needs based on the tar volume required:

• Waterproofing a small boat — 20-40 liters of tar = approximately 200-400 kg of pine wood
• Preserving 100 meters of rope — 5-10 liters = approximately 50-100 kg of wood
• Coating a roof (20 square meters) — 10-20 liters = approximately 100-200 kg of wood
• General community supply for one year — 100-200 liters = approximately 1-2 tons of wood

Simple Pit Method

The most basic tar production requires nothing more than a hole in the ground and a fire.

Setup

1. Dig two pits on a slope — a large upper pit (1 meter diameter, 0.5 meters deep) and a small lower pit (0.5 meter diameter, 0.5 meters deep), connected by a narrow channel (10-15 cm wide, sloping downward)
2. Line the channel with flat stones or clay to create a smooth surface for tar to flow along
3. Place a collection vessel in the lower pit — a ceramic pot or metal container
4. Cover the lower pit with flat stones, leaving only the channel entrance open. This protects the collected tar from the fire’s heat.

Loading and Firing

1. Fill the upper pit with prepared wood billets, stacked vertically
2. Cover the wood with a thick layer of green branches, leaves, or grass
3. Seal with earth — pile 10-15 cm of clay-rich earth over the green layer, leaving a small vent hole at the top
4. Light from the top — ignite the wood through the vent hole
5. Control the burn — the fire should smolder, not blaze. If flames appear, add more earth to reduce air supply. You want slow pyrolysis, not combustion.

Collection

• Tar begins flowing through the channel into the collection vessel after 3-6 hours
• The process runs for 8-24 hours depending on the quantity of wood
• Check the collection vessel periodically; replace it when full
• The tar emerges mixed with wood vinegar — a thin, sharp-smelling acidic liquid
• Allow the mixture to settle for 24 hours; tar sinks, wood vinegar floats on top
• Pour off the wood vinegar (save it — useful as a disinfectant, insect repellent, and soil acidifier)

Drum/Retort Method

If you have access to a metal drum or large metal pot, this method gives better yields and control.

Equipment

• A large metal container (50-200 liters) with a tight-fitting lid
• A small metal pipe (1-2 cm diameter) fitted through a hole near the bottom of the drum
• A collection vessel
• A fire pit or stone fireplace large enough to support the drum

Process

1. Drill or punch a hole near the bottom of the drum, just above the base
2. Insert the outlet pipe through this hole and seal around it with clay. The pipe should extend 30-50 cm outside the drum and angle downward.
3. Fill the drum with prepared wood billets, packed tightly
4. Seal the lid — clamp, weight, or wire the lid shut. Seal the rim with clay paste. The only opening should be the outlet pipe.
5. Build a fire around and beneath the drum. You are heating the wood from the outside without allowing air inside.
6. Maintain steady heat — the fire should be vigorous enough to heat the drum walls to the point where wood inside begins decomposing (300-500 C internal temperature)
7. Collect products — liquids begin dripping from the outlet pipe after 1-2 hours. First comes wood vinegar (thin, clear, acidic), then tar (dark, viscous).

Gas Collection

The gases produced during distillation are themselves flammable. If you extend the outlet pipe and light the gas emerging from it, it burns with a steady flame — this is wood gas. While not easily stored with simple technology, it can be burned directly for additional heating during the process, improving overall efficiency.

Separating Products

The liquid that drips from the retort is a mixture. Separate it into its components:

1. Settling — pour the liquid into a tall, narrow vessel and wait 12-24 hours. Three layers form:
   • Top: light oils and turpentine (thin, volatile, strong smell)
   • Middle: wood vinegar / pyroligneous acid (thin, acidic, brownish)
   • Bottom: tar (thick, dark, sticky)
2. Decanting — carefully pour off each layer in sequence
3. Further purification — if needed, reheat the tar gently to drive off remaining water and light fractions, producing a thicker, more durable product

Improving Quality and Yield

Wood Preparation Techniques

• Longer drying — air-drying wood for 3-6 months instead of 2-4 weeks noticeably improves yield
• Finer splitting — smaller pieces (3-5 cm across) produce tar faster and more completely than larger billets
• Pre-warming — stacking wood near the fire pit for several hours before loading drives off surface moisture
• Resin enrichment — scoring living pine trees and collecting the sap that flows out, then adding it to the wood charge, dramatically increases tar yield

Process Optimization

1. Temperature control — too hot and the tar decomposes into gas and carbon; too cool and the wood doesn’t fully break down. Aim for an internal temperature of 350-450 C (judged by the color and behavior of the smoke)
2. Slow and steady — a firing that takes 24 hours produces more tar than one that burns through in 8 hours. Patience is yield.
3. Double distillation — running the raw tar through a second, gentle distillation produces “Stockholm tar” — a refined, thin, penetrating tar that is far superior for wood preservation
4. Recycle the charcoal — the charcoal left after tar extraction is high-quality fuel. Use it in subsequent firings to improve temperature control, or save it for metalworking.

Byproduct Recovery

Wood tar production generates several valuable byproducts:

Byproduct	Description	Uses
Charcoal	Carbonized wood remaining in the kiln	Fuel for metalworking, cooking, water filtration
Wood vinegar	Acidic liquid condensing before tar	Disinfectant, insect repellent, soil amendment, mordant for dyes
Turpentine	Light volatile oil from resinous wood	Solvent, paint thinner, lamp fuel, cleaning agent
Wood gas	Non-condensable gases	Direct burning for heat during the process
Pitch	Tar heated to drive off volatiles	Waterproofing sealant, boat caulking, adhesive

Making Pitch from Tar

Pitch is tar that has been further heated to drive off water and light oils, producing a thicker, harder product:

1. Heat tar gently in an open vessel (outdoors, away from structures)
2. Stir continuously to prevent scorching and ensure even heating
3. Monitor consistency — dip a stick in the tar periodically. When it cools to a hard, brittle solid on the stick, the pitch is done.
4. Pour into molds — pitch can be poured into blocks for storage and transport
5. To use — reheat pitch to soften it, then apply as a sealant or adhesive

Pitch Fires

Heating tar to make pitch is one of the most fire-prone operations in all of pre-industrial chemistry. Hot pitch vapors are extremely flammable. Always heat pitch outdoors, keep sand and earth nearby for smothering fires, and never leave heating pitch unattended.

Scaling Up Production

Community-Scale Operations

For a community that needs regular tar supply:

1. Dedicated tar pit or kiln — build a permanent installation (see Tar Kiln Build)
2. Rotation schedule — fire the kiln every 2-4 weeks, cycling through available wood supplies
3. Wood coppicing — manage a woodland specifically for tar production by coppicing (cutting trees to stumps and harvesting regrowth on 7-15 year cycles). This provides a sustainable, indefinite supply of tar wood.
4. Specialization — tar production benefits from experienced operators. Designate 2-3 community members as tar makers who develop expertise over multiple firings.
5. Storage system — build proper storage facilities (see Storage Containers) to accumulate tar reserves for seasonal needs

Record Keeping

Track your production to optimize over time:

• Wood species and preparation method used
• Weight or volume of wood input
• Firing duration and conditions (weather, temperature observations)
• Volume of tar, wood vinegar, and turpentine collected
• Quality observations (viscosity, color, smell)
• Charcoal weight recovered

After 5-10 firings, patterns will emerge that guide you toward your best wood sources, optimal preparation, and ideal firing conditions for maximum yield.