What Roofing Tar Is Made Of: Composition and Uses

Roofing tar is a common waterproofing and sealing material used in roofing systems and construction. This article explains what roofing tar is made of, how it’s produced, the different types, performance characteristics, application methods, health and environmental concerns, and common alternatives. A clear understanding of roofing tar helps homeowners and professionals choose the right product and handle it safely.

Aspect	Key Points
Primary Ingredients	Petroleum distillates, coal tar, bitumen/asphalt, fillers
Types	Coal Tar Pitch, Asphalt (Bitumen) Tar, Organic Tars
Uses	Flashing, patching, seam sealing, ponding water areas
Health Concerns	PAHs, VOCs, skin/respiratory irritation
Alternatives	Modified bitumen, liquid rubber, silicone coatings

What Roofing Tar Commonly Contains

Roofing tar is primarily composed of hydrocarbon-based materials derived from either petroleum refining (asphalt/bitumen) or coal processing (coal tar). These base materials are blended with solvents, fillers, tackifiers, and sometimes polymers to modify performance. Additives control viscosity, UV resistance, flexibility, and curing behavior.

Coal Tar Pitch originates from the distillation of coal during coke production and contains a complex mixture of polycyclic aromatic hydrocarbons (PAHs), phenols, and heterocyclic compounds. Its high aromatic content gives coal tar excellent durability and resistance to chemical attack.

Asphalt/Bitumen comes from the vacuum residuum of crude oil refining. It is less aromatic than coal tar and typically contains saturates, aromatics, resins, and asphaltenes. Asphalt-based tars are widely used because they integrate better with modern roofing membranes and emit fewer hazardous PAHs.

Solvents, Fillers, And Additives

Solvents such as mineral spirits, kerosene, or other petroleum distillates are used to adjust viscosity for easier application. They evaporate after application, leaving the tacky tar to cure. Solvent content affects drying time and VOC emissions.

Fillers include mineral powders (e.g., calcium carbonate, silica) and sand to increase body, reduce cost, and alter thermal stability. Fillers also change adhesive and tensile properties.

Polymer Modifiers And Tackifiers like styrene-butadiene-styrene (SBS) or atactic polypropylene are sometimes added to improve elasticity, UV resistance, and low-temperature flexibility. Antioxidants, UV stabilizers, and flame retardants may also be incorporated for specific performance needs.

Types Of Roofing Tar And How They Differ

Coal Tar Pitch is darker, highly aromatic, and historically favored for flat roofs, especially where chemical resistance is required. It resists water, oils, and many industrial chemicals but contains higher levels of carcinogenic PAHs compared to asphalt.

Asphalt-Based Roofing Tar is derived from petroleum and is often labeled as roofing asphalt, bitumen, or tar-based roof cement. It is compatible with asphalt shingles and many membrane systems and generally has lower PAH content.

Cold-Applied Versus Hot-Applied products differ in handling. Cold-applied roof tars are solvent-based or water-emulsified for brush or trowel use. Hot-applied tars are heated to high temperatures for pouring or mopping and are more common with traditional built-up roof systems.

How Roofing Tar Is Manufactured

Coal tar pitch is produced by heating coal at high temperatures in the absence of air (coking), collecting volatile tars, and refining them to achieve a desired viscosity and composition. Final processing removes light ends and adjusts consistency.

Asphalt roofing tar production starts with vacuum residuum from crude oil refining. The residuum is air-blown or oxidized to change molecular structure and achieve the proper hardness and softening point for roofing applications. Blending with solvents, polymers, and fillers occurs to create tailored formulas.

Performance Characteristics And Why They Matter

Waterproofing and Adhesion are fundamental properties of roofing tar. The hydrocarbon matrix forms a continuous film that resists water infiltration and adheres to substrates, flashing, and fastener heads.

Flexibility And Thermal Movement determine whether a roofing tar will crack under temperature extremes. Polymer-modified tars provide greater elasticity and resist thermal cycling more effectively than unmodified tars.

UV Stability And Aging affect service life. Coal tar tends to resist UV-induced degradation better than raw asphalt, but polymer modifiers and coatings can significantly enhance asphalt-based tars.

Common Uses Of Roofing Tar

Patching And Flashing are the most common uses; roofing tar seals seams, nail penetrations, roof edges, and flashing areas where membranes meet vertical surfaces. Its tackiness ensures good adhesion in small repairs.

Built-Up Roofing Systems historically used layers of felt and hot-applied or mopped coal tar or asphalt to create multi-layer waterproof assemblies. Modern systems often replace coal tar with asphalt or modified bitumen.

Waterproofing Details such as vents, chimneys, and curbs often use roof tar as a primer or sealant in conjunction with membranes, metal flashing, or roof coatings to ensure long-term watertightness.

Application Methods And Best Practices

Surface Preparation is critical: surfaces must be clean, dry, and free of loose material or dust. Primers may be required for porous substrates to promote adhesion.

Cold-Applied Products are applied with trowels, putty knives, or brushes. For best results, follow manufacturer instructions regarding substrate temperature and solvent release time before covering.

Hot Mopped Systems require heating boilers and specialized applicators. Safety precautions are mandatory because hot tar can cause severe burns and fire hazards. Heating must be controlled to prevent overheating and degradation of the product.

Health, Safety, And Regulatory Concerns

Coal tar-based products contain PAHs, many of which are classified as carcinogenic or mutagenic. Prolonged skin contact or inhalation of fumes — especially during heating — increases health risks. Regulatory agencies in some regions restrict or discourage coal tar usage because of these concerns.

Volatile Organic Compounds (VOCs) are present in solvent-based tars and contribute to air pollution and indoor air quality problems if used improperly. Proper ventilation, PPE (gloves, goggles, respirators), and adherence to exposure limits are essential.

Disposal And Environmental Controls require attention: liquid and solid residues are considered hazardous in many jurisdictions due to PAH content and must be disposed of according to local hazardous waste regulations.

Environmental Impact And Sustainability

Coal Tar Environmental Concerns stem from PAH contamination in soil and water when spills occur or when roofing materials degrade. Coal tar-based sealants have been restricted for some municipal uses because they can wash into waterways and harm aquatic life.

Asphalt-Based Products generally present fewer acute toxicity concerns but still contribute to petroleum-derived waste and greenhouse gas footprints. Recycling asphalt shingles and using reclaimed materials can reduce environmental impact.

Low-VOC And Bio-Based Alternatives are increasingly available, including waterborne emulsions, rubberized coatings, and bio-asphalt blends that incorporate biomass-derived feedstocks for improved sustainability profiles.

Alternatives To Traditional Roofing Tar

Modified Bitumen Membranes combine asphalt with polymers (SBS, APP) to create flexible, durable sheets that replace many traditional tar applications and offer improved UV and thermal performance.

Liquid Rubber And Elastomeric Coatings are cold-applied, low-VOC options that create seamless waterproof layers ideal for details and ponding areas. They offer excellent elasticity and easy application.

Silicone And Polyurethane Roof Coatings provide long-term UV resistance and waterproofing for many roof types. These coatings are often used to extend the life of existing roofs without full replacement.

Choosing The Right Product For A Project

Match Product Chemistry To Need: use asphalt-based materials for compatibility with asphalt shingles and built-up systems; consider coal tar only where specific chemical resistance is required and where regulations permit its use.

Consider Long-Term Performance including UV exposure, thermal cycling, ponding water, and chemical contacts. Polymer-modified tars often last longer in demanding conditions.

Prioritize Safety And Environmental Regulations by checking local codes, VOC limits, and disposal requirements. Where possible, choose low-VOC, lower-PAH alternatives and ensure qualified professionals handle hot applications.

Frequently Asked Questions About Roofing Tar

Is Roofing Tar The Same As Roof Cement?

Roof cement is a type of roofing tar formulated for patching and flashing; it may be asphalt-based or coal tar-based and often contains solvents for cold application.

Can Roofing Tar Be Used On Shingles?

Small patching is common but broad application over shingles is not recommended because tar can alter shingle performance and aesthetics; use manufacturer-approved sealants for shingle repairs.

Is Coal Tar Still Allowed?

Regulations vary by state and municipality. Some places restrict coal tar for pavement sealants or certain roofing uses due to PAH concerns; always verify local rules.

How Long Does Roofing Tar Last?

Service life depends on formulation, exposure, and substrate. Properly applied polymer-modified products can last decades, while solvent-based patching tars may require maintenance every few years.

Practical Safety Checklist For Handling Roofing Tar

• Use appropriate PPE: chemical-resistant gloves, eye protection, long sleeves, and NIOSH-approved respirators for fumes.
• Ensure ventilation when using solvent-based tars indoors or in confined spaces.
• Control ignition sources during hot applications and store flammables away from open flames.
• Follow disposal rules for residues, containers, and contaminated absorbents per local hazardous waste regulations.