Material
What Is Asphalt Roof Cement? Properties, Performance, and Uses
Also called: roofing tar, plastic cement, flashing cement, roof mastic, asphalt mastic
Asphalt roof cement is a thick, bituminous compound used to seal, bond, and waterproof joints, flashings, and repairs on asphalt-based roofing systems.
In plain English
Asphalt roof cement is a thick, trowel-grade roofing material composed of asphalt, mineral fillers, and fibers, used to seal, bond, and waterproof joints, flashings, and repairs on asphalt-based roofing systems. It adheres to wet or dry surfaces and provides a durable, weather-resistant seal.
How asphalt roof cement works
Asphalt roof cement is a specialized bituminous compound formulated for sealing, bonding, and repairing various roofing components. Composed primarily of asphalt, mineral fillers, and reinforcing fibers, this dense, plastic material is engineered to adhere to a range of surfaces, including asphalt shingles, metal flashings, and masonry at critical roof areas such as ridges, eaves, valleys, and around penetrations. Its structure allows it to conform to irregular surfaces and fill gaps, providing a continuous, watertight barrier.
Functionally, asphalt roof cement is valued for its strong adhesive properties, flexibility, and resistance to weathering. It remains pliable after application, accommodating minor roof movement and thermal expansion without cracking. This performance is crucial for maintaining water drainage integrity along slopes and at vulnerable joints, preventing leaks caused by wind-driven rain or melting snow. The cement’s ability to seal around fasteners and flashing details enhances wind resistance and protects against moisture intrusion at roof edges and transitions.
Asphalt roof cement is commonly used in both new construction and roof repair, particularly on low-slope and steep-slope roofs where additional waterproofing is required at seams, laps, and terminations. Its application extends the service life of roofing systems by reinforcing vulnerable areas and ensuring the roof assembly remains structurally efficient and weather-resistant.
Why it matters for your roof
While useful for repairs, it is not a long-term solution for major roofing issues. It also affects how homeowners, contractors, and specifiers evaluate roof durability, cost, risk, and long-term value.
Benefits
WATERPROOF SEALING
Asphalt roof cement provides a durable, watertight seal that prevents moisture intrusion at flashing, joints, and penetrations.
ADHESION TO MULTIPLE SURFACES
It bonds effectively to asphalt shingles, metal, masonry, and other common roofing substrates, ensuring material compatibility.
WEATHER RESISTANCE
Formulated to withstand UV exposure, temperature fluctuations, and precipitation, asphalt roof cement maintains performance in harsh climates.
REPAIR VERSATILITY
Its pliable composition allows for quick patching of cracks, blisters, and minor leaks, supporting ongoing roof maintenance.
Limitations
UV DEGRADATION
Asphalt roof cement deteriorates under prolonged ultraviolet exposure, leading to cracking, embrittlement, and loss of adhesion over time.
TEMPERATURE SENSITIVITY
Performance declines in extreme cold or heat, causing reduced pliability, improper curing, or slumping on steep slopes.
CHEMICAL INCOMPATIBILITY
Incompatible with certain roofing membranes and materials, potentially causing softening, staining, or membrane degradation at contact points.
SHORT SERVICE LIFE
Asphalt roof cement typically offers a shorter lifespan than most primary roofing materials, requiring more frequent reapplication or repair.
Common problems
UV DEGRADATION
Prolonged ultraviolet exposure causes asphalt roof cement to dry out, crack, and lose adhesion, leading to premature failure.
CHEMICAL INCOMPATIBILITY
Asphalt roof cement can react adversely with certain single-ply membranes, resulting in membrane softening, blistering, or loss of waterproofing.
THERMAL CRACKING
Repeated thermal cycling causes asphalt roof cement to become brittle and develop cracks, allowing water infiltration at vulnerable joints.
POOR WEATHER RESISTANCE
Asphalt roof cement is susceptible to washout or erosion during heavy rain before curing, compromising long-term weatherproofing.
Where you'll see it
EMERGENCY LEAK PATCHING
Asphalt roof cement is ideal for quickly sealing small punctures or cracks in asphalt shingle roofs during active leaks.
FLASHING SEALANT
It is commonly used to bond and waterproof metal flashing joints where water intrusion is likely on sloped asphalt shingle roofs.
SHINGLE TAB ADHESION
Asphalt roof cement secures loose or wind-lifted shingle tabs, preventing blow-offs in high-wind or storm-prone regions.
GUTTER JOINT SEALING
It effectively seals joints and seams in metal gutters attached to asphalt shingle roofs, reducing the risk of water backup and rot.
Don't confuse it with
Not to be confused with similar roofing terms that sound related but perform a different role in the roof assembly.
- asphalt roof cement vs roofing tar
- asphalt roof cement vs polyurethane roof sealant
- asphalt roof cement vs butyl roof sealant
- asphalt roof cement vs flashing cement
Regional & climate notes
Most relevant in: Rain-heavy climates, Snow-heavy climates, Freeze-thaw climates, High-UV climates.
Frequently Asked Questions
What is asphalt roof cement and how is it used in roofing applications?
Asphalt roof cement is a thick, waterproof adhesive used to seal, repair, and bond roofing materials. It is commonly applied to patch leaks, seal flashing, and secure shingles on asphalt-based roofing systems.
What is asphalt roof cement used for in roofing applications?
Asphalt roof cement is used to seal, bond, and repair roofing materials, such as shingles and flashing. It provides waterproofing, fills small cracks, and secures loose components to prevent leaks and weather damage.
Why is asphalt roof cement important for roof repairs and maintenance?
Asphalt roof cement is important for roof repairs and maintenance because it seals leaks, fills cracks, and adheres roofing materials, providing a durable, weather-resistant barrier that helps prevent water infiltration and extends roof life.
How does asphalt roof cement affect the longevity and performance of a roofing system?
Asphalt roof cement provides temporary waterproofing and repairs for roofing systems, but overuse or improper application can trap moisture, cause cracking, and reduce overall roof longevity and performance. Proper use is essential for best results.
How can you evaluate the quality and performance of asphalt roof cement before application?
Evaluate asphalt roof cement by checking for uniform consistency, proper thickness, and absence of separation or lumps. Confirm it meets ASTM D4586 standards and is compatible with your roofing materials for optimal adhesion and weather resistance.
What factors can affect the performance and longevity of asphalt roof cement?
The performance and longevity of asphalt roof cement depend on proper application, weather exposure, UV radiation, temperature fluctuations, substrate compatibility, and the presence of moisture or debris during installation.
Related terms
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