Roof Sealing

Part of Petroleum and Tar

Using tar and pitch products to create durable, waterproof roofs for buildings of all types.

Why This Matters

A leaking roof degrades everything beneath it. Water dripping onto wooden framing causes rot. Moisture on stored food causes spoilage and mold. Damp living spaces breed illness. A single winter with a leaking roof can destroy supplies that took an entire growing season to accumulate. In a rebuilding scenario, waterproof roofing is not a comfort — it is a survival requirement.

Traditional roofing materials — thatch, wooden shingles, slate, and clay tiles — all have vulnerabilities to water infiltration. Thatch must be steeply pitched and regularly maintained. Shingles curl and split over time. Even slate and tile roofs leak at joints, valleys, and penetrations. Tar and pitch products address these vulnerabilities by providing a continuous, impermeable membrane that seals every gap, joint, and fastener hole.

The development of tar-based roofing in the early 19th century was a major construction advance. Flat roofs became practical for the first time, since they no longer depended on steep pitch to shed water. Built-up roofing — layers of fabric and tar — could waterproof any surface at any angle. These same techniques are fully achievable with the materials and tools available to a rebuilding society.

Roofing Materials You Can Produce

Tar and Pitch

The primary waterproofing agent. Use pine tar, petroleum residue, or coal tar pitch — any will work, though each has characteristics suited to different approaches:

Material	Best For	Advantages	Disadvantages
Pine pitch	Over wood substrates	Flexible, bonds well to wood, easy to repair	Softens in extreme heat
Petroleum residue	Flat and low-slope roofs	Very durable, cheap if petroleum available	Can be brittle in cold
Coal tar pitch	Heavy industrial roofs	Most water-resistant, self-healing	Strong odor, harder to apply

Roofing Fabric

The reinforcement layer between tar coats. Options:

• Burlap/hessian: Widely available from plant fibers, strong enough for roofing
• Canvas: Excellent if available — heavier weave provides better reinforcement
• Reed or grass mats: Woven mats from reeds, cattails, or grass — the most accessible option
• Wool felt: Traditional roofing material — wool fibers compress into a dense, absorbent mat that holds tar well
• Salvaged fabric: Any tightly woven, heavy fabric works

Gravel and Sand

Protective surface layer that shields the tar from UV degradation and physical damage.

Built-Up Roofing (BUR) — The Standard Method

Built-up roofing creates a waterproof membrane by alternating layers of tar and fabric. This is the same principle used in commercial flat roofing for over 150 years.

Preparing the Roof Deck

1. The deck must be solid, smooth, and dry. Plank decking, plywood (if salvaged), or tightly laid boards work well.
2. Fill any gaps between boards with thin strips of wood or caulking. The membrane will bridge small gaps, but large ones invite failure.
3. Sweep clean — any debris under the membrane creates pressure points that puncture eventually.
4. If the deck is damp, wait for dry weather. Moisture trapped under the membrane cannot escape and causes blistering.

Layer-by-Layer Application

Base coat:

1. Heat tar or pitch until it flows freely (100-130°C)
2. Mop or brush a thin, even coat over the entire deck surface
3. Work in sections small enough that the tar stays hot during application
4. This coat seals the wood and provides adhesion for the first fabric layer

First fabric layer:

1. Roll out fabric directly onto the wet base coat
2. Press down firmly with a roller, board, or by walking on it
3. Overlap adjacent strips by at least 10 cm (4 inches)
4. Stagger the overlaps — avoid having all seams line up in the same place
5. The fabric should be fully saturated — no dry spots

Second tar coat:

1. Mop hot tar over the first fabric layer, saturating it completely
2. Use enough tar that a thin pool forms on the surface
3. Work out any wrinkles or air pockets in the fabric

Second fabric layer:

1. Apply as before, but offset the seams from the first layer by at least 15 cm
2. This ensures that no single point on the roof has less than two layers of reinforcement

Third tar coat:

1. Saturate the second fabric layer as before

Optional additional layers: For maximum durability, continue alternating fabric and tar. Three fabric layers (a “4-ply” roof) is standard for commercial quality. Two layers is adequate for most residential applications.

Surface protection:

1. While the top tar coat is still hot and sticky, spread clean gravel or coarse sand evenly across the entire surface
2. Press into the tar with a board or roller
3. This gravel layer protects the membrane from UV radiation, physical damage, and thermal cycling
4. Use pea-sized gravel (5-10 mm) — too large sits loose, too small washes away

Hot Application Temperature

Apply tar at the lowest temperature that allows good flow and saturation. Tar applied too hot soaks through the fabric and fails to build adequate membrane thickness. Tar applied too cold does not penetrate the fabric and creates poor inter-layer bonding. Test on a scrap piece of fabric first — the tar should soak partway through but not drip through.

Pitched Roof Applications

For steeply pitched roofs (shingle, thatch, or tile), tar and pitch serve as sealants rather than primary membranes.

Under Shingles

1. Apply a base layer of tar-saturated fabric to the roof deck before installing shingles
2. Focus on vulnerable areas: valleys, ridges, eaves, and around any penetrations (chimneys, vents)
3. This provides a secondary waterproof layer if shingles fail

Valley Lining

Roof valleys — where two roof planes meet — concentrate water flow and are the most common leak point:

1. Cut fabric strips wide enough to extend 30 cm up each roof slope from the valley center
2. Saturate with hot tar and lay in the valley
3. Apply a second saturated layer offset from the first
4. Install shingles or tiles over the valley lining, leaving the center clear for water flow

Flashing Alternatives

Where a roof meets a wall, chimney, or other vertical surface, water must be directed away from the joint:

1. Cut fabric strips long enough to run 15 cm up the vertical surface and 15 cm onto the roof
2. Apply hot tar to both surfaces
3. Press the fabric into the tar, forming a right angle
4. Apply additional tar over the fabric
5. Apply a second fabric strip offset from the first
6. This tar-and-fabric flashing is not as durable as metal flashing but is effective and easily renewed

Flat Roof Design Considerations

Flat roofs sealed with tar require careful design to avoid water ponding:

Drainage

• No roof should be truly flat. Provide at least a 1:50 slope (2%) toward drainage points
• Install scupper openings or drain pipes at low points
• A ponding area on a flat tar roof will eventually penetrate any membrane
• After rain, inspect for standing water and correct any ponding areas by building up the low spots with additional tar and gravel

Expansion Joints

• Large flat roofs should have expansion joints every 10-15 meters to accommodate thermal movement
• Create joints by leaving a 5 cm gap in the membrane, bridged by a loose flap of tar-soaked fabric that can flex with movement
• Without expansion joints, the membrane will crack at the weakest point

Maintenance and Repair

Annual Inspection

Every spring (after freeze-thaw cycles) and autumn (before winter rains), inspect your tar roof:

1. Walk the entire surface looking for:

   • Cracks in the tar surface
   • Bare spots where gravel has displaced, exposing tar to UV
   • Blisters (bubbles in the membrane indicating trapped moisture)
   • Ponding areas
   • Lifted edges or seams
   • Deterioration around penetrations

2. Repair cracks: Clean the area, apply hot tar, lay a fabric patch extending 10 cm beyond the crack on all sides, and cover with more hot tar and gravel.

3. Fix bare spots: Sweep clean and apply a fresh coat of tar with gravel.

4. Address blisters: Cut an X through the blister with a knife, peel back the flaps, let any moisture dry, press the flaps back into hot tar, and patch over with fabric and tar extending beyond the cut.

Expected Lifespan

Roof Type	Layers	Expected Life	With Maintenance
2-ply BUR	2 fabric + 3 tar	10-15 years	20-25 years
3-ply BUR	3 fabric + 4 tar	15-20 years	25-35 years
4-ply BUR	4 fabric + 5 tar	20-30 years	30-50 years

Material Quantities

For planning purposes, per 10 square meters of roof:

Material	2-Ply Roof	3-Ply Roof
Tar/pitch	25-35 liters	35-50 liters
Fabric	22-25 m² (including overlaps)	33-37 m²
Gravel	200-300 kg	200-300 kg

Working Safely on Roofs

Tar roofing combines two significant hazards — hot material and height.

• Burns: Hot tar causes severe, deep burns. Wear heavy gloves, long sleeves, closed shoes (not sandals), and eye protection. Carry tar in buckets only half-full to prevent sloshing.
• Falls: Do not work on wet or icy roof surfaces. Use safety ropes if available. Have a spotter on the ground.
• Fumes: Hot tar releases irritating vapors. Work upwind of the application area. Take breaks if you feel dizzy or nauseated.
• Fire: Keep firefighting sand on the roof. Never leave heating tar unattended. Keep the tar-heating station on the ground, not on the roof. Haul hot tar up in small, manageable quantities.

Never Heat Tar on the Roof

Heat tar on the ground and carry it up in small buckets. A fire in a tar kettle on a roof can rapidly ignite the roof itself and the building below. Keep the heating operation on bare ground, well away from the building, with sand and a lid ready.