Pitch Making

Part of Petroleum and Tar

Converting raw tar into pitch — the concentrated, refined form used for waterproofing, adhesion, and sealing.

Why This Matters

Tar and pitch are often spoken of interchangeably, but they are distinct products with different properties and applications. Tar is the raw product of wood pyrolysis or petroleum distillation — a complex liquid containing water, light volatile oils, phenols, and heavy hydrocarbon compounds. Pitch is what remains after you cook the tar to drive off water and light volatiles. It is more concentrated, harder, more water-resistant, and more durable than raw tar.

The distinction matters because many applications require pitch specifically. Raw tar is too thin and volatile for hull waterproofing — it seeps through seams rather than sealing them and evaporates within months. Pitch, being thicker and harder, fills gaps, stays in place, and lasts for years. Conversely, raw tar is better for applications like rope treatment and surface coating where penetration into fibers and wood grain is desired.

Pitch making is one of the oldest chemical manufacturing processes in human history. Archaeological evidence shows pitch production dating to at least 200,000 years ago, when Neanderthals produced birch bark pitch for hafting stone tools. The process is simple in principle but requires attention to detail — undercooked pitch is too soft, overcooked pitch is too brittle, and pitch heated carelessly catches fire.

Raw Materials

Pitch can be made from any tar source:

Wood Tar

• Pine tar: The most common source in forested regions. See Pine Tar for production methods. Produces a flexible, fragrant pitch ideal for marine and general waterproofing.
• Birch bark tar: Produces an exceptionally adhesive pitch. Historically used for tool hafting and small-scale bonding. Requires large quantities of birch bark.
• Other softwood tars: Spruce, fir, and larch tars all work, though yields and quality vary.

Petroleum-Derived Tar

Heavy petroleum fractions and residues can be cooked into pitch. Petroleum pitch tends to be harder and more brittle than wood-derived pitch but is excellent for road building, foundation waterproofing, and industrial applications.

Coal Tar

A byproduct of coal coking (heating coal in the absence of air to make coke for metallurgy). Coal tar pitch is extremely durable and water-resistant but contains more harmful compounds. Available only where coal is being processed.

The Pitch-Making Process

Equipment Needed

• Cooking vessel: A wide, shallow metal or ceramic pot is ideal. Wide and shallow gives more surface area for evaporation and easier stirring. A deep, narrow pot slows evaporation and makes it harder to monitor consistency.
• Heat source: A controllable fire or stove. You need steady, moderate heat — not fierce flames.
• Stirring tool: A long-handled wooden paddle or metal rod. Length matters — hot pitch splatters.
• Molds or containers: For the finished pitch. Clay pots, bark containers, or simply a flat stone surface.
• Fire suppression: A tight-fitting lid for the cooking vessel and a bucket of sand nearby.

Step-by-Step Process

1. Strain the raw tar

Before cooking, strain the tar through coarse cloth to remove wood chips, bark fragments, ash, and sediment. These inclusions create weak spots in finished pitch and cause sputtering during cooking.

2. Load the cooking vessel

Fill the vessel no more than half full. Tar froths and expands during cooking — a full vessel will overflow. An overflowing vessel of hot tar near a fire is an emergency.

3. Begin heating

Apply moderate heat. The tar should warm gradually, not come to a rapid boil. Target a gentle simmer, not a rolling boil.

4. First phase — water removal (30-60 minutes)

Water in the tar causes vigorous bubbling and spattering initially. Stir occasionally. The bubbling will subside as water evaporates. The tar will thin as it warms, then begin to thicken as water leaves.

5. Second phase — light volatile removal (1-3 hours)

After the water is gone, lighter tar oils begin evaporating. These are turpentine-related compounds. The tar darkens, thickens, and the smell shifts from sharp and resinous to deeper and more mellow. Stir regularly to prevent skin formation on the surface and to ensure even heating.

Fire Danger

The vapors released during this phase are highly flammable. If cooking over an open fire, ensure flames do not lap above the rim of the vessel. If the tar ignites, immediately cover the vessel with a tight-fitting lid to smother the flame. Do NOT add water — it will cause explosive spattering of burning tar.

6. Testing consistency

Periodically test the pitch by dripping a small amount from the stirring tool onto a cool surface (a stone or piece of metal). Let it cool for 30 seconds and assess:

• Too soft: Still sticky and deformable when cool. Continue cooking.
• Good (soft pitch): Sets to a firm but slightly flexible state. Can be dented with a fingernail. Good for caulking, rope treatment, and flexible waterproofing.
• Good (hard pitch): Sets rigid. Cannot be dented with a fingernail but does not shatter when tapped. Good for hull coating, sealing, and adhesive.
• Too hard: Shatters like glass when tapped or dropped. You have overcooked it. This can be rescued by melting again and adding back some raw tar or oil.

7. Pour or mold

When the desired consistency is reached, remove from heat and pour into molds or containers. Work quickly — pitch thickens rapidly as it cools.

Common mold forms:

• Balls or cakes: Pour into greased bowls or cupped leaves. Easy to store and transport.
• Sticks or cylinders: Pour into bamboo tubes, hollow reeds, or rolled bark. Convenient for applying directly to seams.
• Blocks: Pour into rectangular molds lined with sand. Good for long-term storage.
• Directly into storage pots: For bulk storage, pour into glazed ceramic jars.

Controlling Pitch Properties

The key variable is how long and how hot you cook the tar. This determines the final consistency.

Cooking Level	Time (typical)	Temperature	Consistency	Best For
Light cook	1-2 hours	120-150°C	Thick liquid, sticky	Rope coating, wood penetration
Medium cook	2-4 hours	150-180°C	Soft solid, flexible	Caulking, leather work
Full cook	4-8 hours	180-220°C	Hard solid, rigid	Hull coating, sealing
Over-cooked	8+ hours	220°C+	Brittle, glassy	Blending with softer materials to salvage

Additives for Modified Properties

For increased flexibility (marine pitch):

• Add 10-15% by weight of animal fat (tallow, fish oil) near the end of cooking
• Mix in 5-10% beeswax after removing from heat
• These prevent cracking in cold weather and allow the pitch to flex with hull movement

For increased hardness (construction pitch):

• Cook longer at higher temperature
• Add 5% sulfur (powdered, stirred into hot pitch) — this cross-links the molecules
• Mix in fine mineral powder (chalk, powite rock dust) as filler

For improved adhesion (bonding pitch):

• Add finely powdered charcoal (15-20% by weight)
• For birch pitch adhesive, add heated beeswax (10%)
• Resin from wounds on living pine trees can be stirred in for extra tackiness

For thinning (brush application):

• Add turpentine (spirits of turpentine recovered during tar making)
• Add kerosene or light petroleum fraction
• This creates a “varnish” consistency that can be brushed on surfaces

Reheating and Reworking

One of pitch’s great advantages is that it can be reheated and reworked indefinitely:

1. Break solid pitch into pieces
2. Place in a vessel and heat gently
3. It softens and becomes workable again
4. Add raw tar if it has become too hard
5. Add heat time if it is too soft
6. Pitch does not “expire” — properly stored, it lasts centuries

This means pitch scraps, failed batches, and recovered pitch from demolished structures can all be recycled. Nothing is wasted.

Yield Expectations

Cooking tar into pitch reduces volume significantly as water and volatiles evaporate:

Starting Material	Pitch Yield (by volume)	Pitch Yield (by weight)
Raw pine tar	50-70%	55-75%
Birch bark tar	60-75%	65-80%
Petroleum heavy fraction	80-95%	85-95%
Coal tar	50-65%	55-70%

From 10 liters of raw pine tar, expect 5-7 liters of finished pitch. The “lost” volume is water and turpentine (which you should capture with a condenser if possible — turpentine is valuable).

Quality Assessment

Good pitch meets these criteria:

• Color: Deep black or very dark brown — uniformly dark throughout
• Fracture: Clean break, not crumbly or granular
• Smell: Deep, pleasant tar smell — not acrid or burnt (burnt smell indicates overheating)
• Adhesion: When warmed to hand temperature, sticks to clean wood
• Water resistance: A piece placed in water for 24 hours shows no absorption or softening
• Flexibility (for marine pitch): A thin strip can be bent slightly without cracking at room temperature

Common Problems and Solutions

Problem	Cause	Solution
Pitch is too soft	Undercooked	Reheat and cook longer
Pitch is too brittle	Overcooked	Melt and add 10-15% raw tar or oil
Gritty texture	Debris in raw tar	Strain through cloth and remelt
Pitch has burnt smell	Overheated	Start fresh — burnt pitch has degraded compounds
Does not stick to wood	Surface contamination	Ensure wood is clean, dry, and warm
Cracks in cold weather	Insufficient flexibility	Add tallow or beeswax

The Chew Test

Historically, pitch quality was tested by chewing a small piece. Good pitch softens slowly in the mouth, becomes pliable, and has a characteristic tar flavor without bitterness. Bitter pitch has been overheated. While not recommended as a primary quality test, this traditional method actually works — pitch was commonly chewed in Scandinavian and North American cultures, and was believed to have dental health benefits from its antiseptic phenol content.