Meta description: Learn what asphalt plastic roofing cement is, where it works, how to apply it, and when a different roof repair material is the better choice.
Asphalt plastic roofing cement is a thick, asphalt-based sealant used for certain roof repairs and flashing details. It can help seal small gaps, secure roofing components, and patch localized damage, but it is not a universal leak fix or a substitute for replacing worn-out roofing. Choosing the right product—and following its label—matters because asphalt formulas, compatible surfaces, weather limits, and application methods vary. This guide explains what the material does, how to use it carefully, and when to call a roofing professional.
What Is Asphalt Plastic Roofing Cement?
Asphalt plastic roofing cement, often called plastic roof cement, asphalt roof cement, or roofing mastic, is a pliable, paste-like roofing material. Typical formulas use asphalt with mineral fillers and other additives. Some products contain reinforcing fibers; others are fiber-free. “Plastic” generally describes the material’s workable consistency, not a plastic-sheet ingredient or a guarantee of lasting flexibility.
The cement is commonly sold in cans or pails for trowel application and in cartridges for use with a caulking gun. Some formulas are labeled for wet-surface or emergency repairs, while others require a dry, clean surface. The package instructions determine what a specific product can do. Products with similar names may not have the same ingredients, approved uses, or application limits.
Roofing cement is different from asphalt shingles, roofing felt, and liquid roof coatings. It is a localized repair material, not a complete roofing system. It is also distinct from water-based or elastomeric coatings, which are generally spread over larger areas and have separate surface-preparation and coverage requirements.
Common Uses for Plastic Roof Cement
When the product label allows, asphalt plastic roofing cement may be used to seal small, localized areas or help secure roofing components. Common applications include:
- Sealing small gaps around flashing, roof edges, and certain penetrations.
- Embedding reinforcing fabric or roofing mesh over a small crack or seam, when the manufacturer specifies that method.
- Securing loose tabs or edges on compatible asphalt shingles as a temporary or product-approved repair.
- Patching limited damage in some built-up or modified-bitumen roofing assemblies.
- Sealing nail heads or fasteners in repair situations where the roof system and product instructions permit it.
Compatibility is essential. A cement made for asphalt roofing may not be suitable for every membrane, metal, plastic, painted surface, or existing coating. Some materials can soften, stain, or fail to bond when exposed to an incompatible sealant. Check the product label and, if needed, the roofing-system manufacturer’s guidance before applying it.
Roof cement is best viewed as a repair material for defined spots, not as a way to coat an entire roof or hide widespread deterioration. Applying a thick layer over a large area may trap moisture, complicate future repairs, or obscure damage without resolving the source of a leak.
How to Choose the Right Roofing Cement
Start with the roof material and the repair location. A product intended for asphalt shingles may not be approved for a rubber membrane, metal flashing, or a low-slope roof. Read the label for approved substrates, surface conditions, application temperature, drying or curing guidance, and any restrictions on use near gutters or roof drains.
Compare the product’s stated purpose with the actual problem. A cartridge may work for a narrow seam, while a trowel-grade cement may be more practical for a patch that needs reinforcement. Neither format makes a repair permanent by itself; the roof’s condition and the quality of the repair matter.
| Selection factor | What to check |
|---|---|
| Roofing material | Confirm that the formula is listed for the specific shingle, membrane, metal, or other surface. |
| Surface condition | Check whether the cement requires a dry surface or permits application to a damp one. |
| Repair size | Match the package format and intended use to the small area being repaired. |
| Weather limits | Review minimum and maximum application temperatures and rain-related instructions. |
| Safety information | Read the label and Safety Data Sheet for ventilation, protective equipment, and cleanup directions. |
For example, Henry’s product information describes a specific wet-patch sealant, while GAF’s roof cement information covers products with their own intended uses. These examples are not interchangeable instructions: the exact container label takes precedence.
How to Apply Asphalt Plastic Roofing Cement
Roof repairs involve fall hazards, and even a small patch can be unsafe on a steep, wet, icy, or fragile roof. If access is not secure or the damage is beyond a minor repair, a qualified roofing contractor is the safer choice. Do not climb onto a roof during rain, high winds, or other hazardous conditions.
Prepare the Repair Area
Identify the likely source of the leak before applying cement. Water can travel beneath roofing materials, so the visible ceiling stain may not be directly below the roof opening. Remove loose debris and any failed, detached material only if the product instructions call for it and the area can be accessed safely. Do not cover wet, deteriorated, or unstable materials unless the product is explicitly designed for those conditions.
Check the forecast and the product’s temperature and weather requirements. Many roof cements need suitable conditions to adhere and set. “Wet patch” on a label does not mean the product can be applied in every storm or over every wet surface; follow the specific directions.
Apply the Cement as Directed
Use a compatible trowel or caulking gun, depending on the product. Spread or tool the cement only over the specified repair area and at the recommended thickness. For a reinforced patch, use the type of fabric and layering method the manufacturer calls for. Extra material is not necessarily extra protection: oversized or overly thick patches can crack, hold debris, or interfere with drainage.
Keep roof drains, gutters, and ventilation openings clear. Do not apply cement where it could block water flow or cover a component that needs to move or be serviced. Let the repair set for the time stated on the label, and avoid walking on or disturbing it during that period.
Inspect the Result
After the product has had the stated time to set, inspect the area from a safe location. Watch for renewed water entry during suitable weather, but remember that a roof repair can require more than one inspection to confirm performance. If leakage continues, the cause may be elsewhere or the roofing assembly may need a larger repair.
Safety, Storage, and Cleanup
Roofing cement can be difficult to remove and may contain petroleum-derived ingredients. Avoid skin and eye contact, use the protective equipment specified on the product label, and provide ventilation when working in enclosed spaces. Keep containers away from flames, sparks, and other ignition sources if the label identifies the product as combustible or flammable. Never assume that all formulas have identical hazards.
Read the container label and Safety Data Sheet before use. The Occupational Safety and Health Administration’s hazard communication resources explain how chemical labels and Safety Data Sheets communicate workplace hazards. For a household repair, the product’s own safety instructions remain the practical source for its handling requirements.
Close containers tightly and store them as directed, away from children, pets, excessive heat, and ignition sources where applicable. Do not pour leftover cement, solvent, or cleanup material into a drain. Follow local rules and the manufacturer’s disposal instructions; some roofing products may require special handling.
Roofing Cement Versus Other Repair Materials
Roof cement is only one option for roof maintenance. The appropriate material depends on the roofing system, the size of the damaged area, and whether the underlying structure is sound.
| Material or repair | Typical role | Important limitation |
|---|---|---|
| Asphalt plastic roofing cement | Localized sealing or patching where the product is approved. | Not suitable for every roof material or widespread roof failure. |
| Roofing sealant in a cartridge | Small seams or joints specified by the manufacturer. | Adhesion and movement tolerance vary by formulation. |
| Liquid roof coating | Protective coverage over an eligible roof surface. | Requires system-specific preparation, coverage, and conditions. |
| Replacement shingles or membrane repair | Replacing damaged components or restoring a roof assembly. | May require a roofer to maintain proper installation and flashing details. |
A sealant can sometimes slow a leak, but it cannot restore rotten decking, failed flashing, extensive membrane damage, or a roof that has reached the end of its service life. A proper repair may require removing materials to inspect the layers underneath.
Common Mistakes to Avoid
- Using the wrong formula: A product intended for one roof type may not adhere to another or may damage the surface.
- Applying cement over unresolved damage: Covering a large crack, loose flashing, or deteriorated substrate can conceal the problem rather than fix it.
- Ignoring surface and weather requirements: Temperature, moisture, and cleanliness can affect adhesion and curing.
- Overapplying the material: Thick, broad layers may interfere with drainage and make later repairs harder.
- Working unsafely: A small repair is not worth the risk of a fall. Use a contractor when roof access is hazardous.
- Assuming a patch is permanent: Recheck the repair and investigate if water intrusion returns.
When to Call a Roofing Professional
Professional inspection is appropriate when a leak persists after a repair, multiple areas are damaged, the roof feels soft underfoot, shingles are widely missing, or flashing has separated from a chimney or wall. A contractor should also assess water intrusion near electrical fixtures, structural damage, or suspected mold, and any repair involving a steep or high roof.
In the United States, licensing and insurance requirements vary by state and locality. Homeowners can check local requirements, request proof of insurance, and obtain a written description of the proposed work. The estimate should explain whether the contractor plans to patch the surface, replace damaged roofing components, or inspect underlying materials.
Frequently Asked Questions
Is asphalt plastic roofing cement waterproof?
It is designed to help seal certain roofing repairs, but performance depends on the exact formula, surface, installation, and exposure. It should not be treated as a guarantee against leaks or as a replacement for sound roofing materials.
Can roofing cement be applied to a wet roof?
Only if the specific product is labeled for that condition and the manufacturer’s directions permit it. Some products require a dry surface. A wet roof can also be dangerously slippery, so product claims do not remove the need for safe working conditions.
Can it be used on shingles?
Some roof cements are approved for certain asphalt-shingle repairs, but the instructions and application method differ by product. Confirm compatibility and avoid applying material broadly across shingle surfaces.
How long does a roof-cement repair last?
There is no universal lifespan. Durability depends on the roof assembly, preparation, weather exposure, and whether the underlying defect was corrected. Persistent or returning leaks warrant further inspection rather than repeated surface patching.