Tar roof repair means sealing a roof leak with an asphalt-based roofing cement, troweled over a clean, dry surface and reinforced with fabric. It works as a fast, low-cost stopgap on asphalt shingles, roll roofing, and built-up (tar and gravel) roofs. It is the wrong fix for EPDM rubber, TPO, and PVC membranes, where the petroleum in the tar breaks the material down. Expect a patch to buy you one to three years, not a permanent repair.
The catch with tar is not how you apply it. It is knowing which surface you are standing on, which product matches it, and how long the fix will actually hold. Get those three right and a tar patch is a legitimate emergency tool. Get them wrong and you spread a mess that voids a warranty and hides a bigger problem.
What roofing tar actually is in 2026
Most products sold as roofing tar today are not true tar. They are asphalt (bitumen) plastic roofing cement, a trowel-grade sealant that meets ASTM D4586, the standard for asbestos-free asphalt roof cement. True coal-tar pitch is now rare and used mainly in hot, industrial built-up roofing. When a homeowner buys a tub labeled roofing tar, roof cement, or wet patch, it is almost always cold-applied asphalt cement.
Cold-applied cement comes ready to use in a tub or a caulk tube. You spread it with a trowel or a caulk gun, and it cures as the solvents flash off. Common named products include Henry 208R Wet Patch, Black Jack All-Weather Roof Cement, Gardner, and Karnak 19. For the full breakdown of grades and how to apply each, see our guide to roofing cement types and how to apply them.
Hot tar is a different job. Asphalt or coal-tar pitch is melted in a kettle to roughly 400 to 500 degrees Fahrenheit and mopped onto low-slope built-up roofs. That is professional work, not a homeowner patch.
Tar, roofing cement, and wet patch: the terms untangled
Roofing tar, roof cement, and wet patch describe overlapping products with different jobs. Sorting them out matters because the wrong grade will not bond to a damp roof, and the wrong product will not stick at all. Here is what each term means and where it fits.
| Term | What it is | Best use | Bonds to a wet surface? |
|---|---|---|---|
| Roofing tar (generic) | Loose name for asphalt cement or coal-tar pitch | Marketing catch-all | Depends on the product |
| Plastic roofing cement (ASTM D4586) | Trowel-grade asphalt mastic | Flashing, seams, small holes | Dry surface only |
| Wet patch cement | Asphalt cement formulated for damp surfaces | Emergency leaks in the rain | Yes |
| Roof sealant or caulk | Elastomeric or polyurethane in a tube | Fine cracks, fastener heads | Product-specific |
| Hot tar or coal-tar pitch | Melted bitumen applied at 400 to 500 degrees | Built-up and tar-and-gravel roofs | No, pro application |
Which roofs tar works on, and which it ruins
Asphalt roofing tar bonds to other asphalt-based and porous surfaces and destroys single-ply rubber and plastic membranes. The petroleum solvents that make asphalt cement sticky swell and break down EPDM rubber, and they are incompatible with TPO and PVC, which need heat-welded or manufacturer-approved patches. Putting tar on a rubber or plastic flat roof can void the membrane warranty and widen the damage. This is the mistake most tar guides skip, so check your surface against the table before you open the tub.
| Roof surface | Asphalt tar or cement? | Why |
|---|---|---|
| Asphalt shingles (3-tab or architectural) | Yes, as a spot patch | Same asphalt chemistry, bonds well |
| Roll roofing (asphalt) | Yes | Asphalt base |
| Built-up, tar and gravel (BUR) | Yes | Designed around asphalt |
| Modified bitumen | Yes, with compatible cement | Asphalt base |
| Metal flashing and seams | Yes, as a sealant, used sparingly | Bonds to clean metal |
| Concrete or masonry | Yes | Porous, holds the cement |
| EPDM rubber | No, never | Petroleum swells and degrades the rubber |
| TPO | No | Needs a heat-welded or approved patch |
| PVC single-ply | No | Chemically incompatible |
| Wood shakes | Avoid | Traps moisture and rots the wood |
How to patch a roof leak with tar, step by step
On an asphalt shingle, roll, or built-up roof, a reinforced cement patch is a solid emergency fix. The process below uses standard plastic roofing cement on a dry surface. For the wider set of options beyond tar, our step-by-step roof leak fix covers when to patch and when to stop.
- Wait for dry weather. Standard asphalt cement bonds best between 40 and 70 degrees Fahrenheit on a dry surface. If the roof is wet and you cannot wait, switch to a wet patch cement.
- Find and clean the leak source. The entry point is often uphill of the interior stain, so inspect above the wet spot. Sweep off debris, loose granules, and dirt.
- Dry the area. Wipe it with a rag and remove any standing water. Asphalt cement will not grab a dirty, greasy, or wet surface.
- Trowel on the first coat. Spread a thin layer of cement, about one eighth of an inch, extending 2 to 3 inches past the damage on every side. Thin coats cure and flex. Thick blobs crack.
- Embed reinforcing fabric. Press polyester or fiberglass roofing membrane fabric into the wet cement over the repair. This is the step most DIY patches skip, and it is what keeps the patch from cracking apart.
- Apply the second coat. Trowel cement over the fabric until the mesh disappears, feathering the edges so water runs off instead of pooling.
- Seal nearby fasteners. Dab cement over any exposed nail or screw heads next to the repair.
- Let it cure. Most cements skin over in a few hours and fully cure in 24 to 72 hours, depending on temperature and thickness.
Patching a shingle tear or nail pop with tar
A torn tab or a popped nail is the most common asphalt shingle repair, and tar handles it in four steps. Work in warm weather when the shingle is pliable so you do not crack the tab.
- Lift the damaged shingle tab gently.
- Apply a coat of cement under the tear, then press the shingle back down.
- Re-nail the shingle if it lifted, driving roofing nails into sound decking.
- Cover the tear and each nail head with a top coat of cement.
Hot tar roof repair, and when it is a pro job
Hot tar roof repair means melting asphalt or coal-tar pitch in a kettle and mopping it onto a built-up or tar-and-gravel roof, then re-embedding gravel or a cap sheet. It repairs the same low-slope systems it built. Because it involves material near 400 to 500 degrees, open kettles, and fumes, it is a licensed contractor job, not a DIY patch.
Fewer crews still run hot kettles, and many have moved to cold-applied cement or torch-down modified bitumen for the same roofs. If you have a gravel-surfaced flat roof, read how these systems are built and fail in our guide to the tar and gravel roof before you decide between a patch and a recover.
How long a tar patch lasts, and what it costs
A tar or asphalt cement patch is a stopgap, not a permanent repair. On a sun-exposed roof, expect one to three years before UV makes the patch brittle and it cracks. In the field, tar patches on a two-year-old roof are already known to fail and leak again. Reinforced patches kept out of direct sun last longer. The materials are cheap.
| Item | Typical cost | Notes |
|---|---|---|
| Roof cement, 10.1 oz tube | $5 to $10 | Small cracks and fasteners |
| Roof cement, 1-gallon tub | $10 to $25 | Multiple patches |
| Wet patch cement, 1 gallon | $15 to $30 | Bonds to damp surfaces |
| Reinforcing fabric roll | $10 to $20 | Roughly doubles patch life |
| Pro hot tar spot repair | $300 to $1,000+ | Built-up roofs, licensed crew |
When you need a fix to hold only until a real repair, a temporary roof repair and tarping plan may protect the interior better than tar alone during a storm.
When tar will not save your roof
Tar covers a symptom. If the leak comes from failed flashing, widespread granule loss, rotted decking, or a roof near the end of its life, a patch hides the problem while water keeps moving inside the assembly. Repeated tar patches on the same roof are a signal that the roof needs a professional repair or replacement, not another coat.
Call a roofer instead of reaching for the tar when you see any of these:
- Multiple leaks appearing across the roof, not one clear spot.
- Decking that feels soft, spongy, or sags underfoot.
- Daylight visible through the deck from the attic.
- An asphalt roof past roughly 20 years of age.
- Leaks around chimneys, skylights, or valleys, which are usually flashing failures, not field damage.
For the wider picture on materials, systems, and when a patch is the right call, start at our roofing basics hub.
Frequently asked questions
Is roofing tar good for a roof leak?
Roofing tar, usually asphalt roof cement, can stop a roof leak quickly as a temporary fix on asphalt shingles, roll roofing, and built-up roofs. It is not a permanent repair, and it should not go on EPDM, TPO, or PVC membranes. Expect a reinforced patch to last one to three years before UV makes it brittle and it cracks.
How long does roof tar last?
A tar or asphalt cement patch typically lasts one to three years on a sun-exposed roof before it dries out, cracks, and leaks again. Patches reinforced with fabric and kept out of direct sun can last longer. Hot-applied tar on a built-up roof lasts far longer because it is part of the roof system, not a surface patch.
Can you put tar on a roof in the rain?
Standard asphalt roof cement will not bond to a wet surface and should be applied on a dry roof between 40 and 70 degrees. For an active leak in the rain, use a wet patch cement, which is made to stick to damp surfaces. Treat it as an emergency measure and redo the repair properly once the roof dries.
What is the difference between roofing tar and roofing cement?
In everyday use the terms overlap. Roofing cement is a specific trowel-grade asphalt mastic that meets ASTM D4586, sold in tubs and tubes for patching. Roofing tar is a looser term that can mean the same cold asphalt cement or true hot coal-tar pitch mopped onto built-up roofs. Most consumer roofing tar is asphalt cement.
Can you use roofing tar on a rubber roof?
No. Asphalt-based roofing tar and cement should never go on an EPDM rubber roof. The petroleum solvents swell and break down the rubber, which can widen the damage and void the membrane warranty. Rubber roofs need EPDM-compatible primer, seam tape, and patches, or a professional repair.
How much does hot tar roof repair cost?
A localized hot tar repair on a built-up or tar-and-gravel roof often runs about $300 to $1,000 or more, depending on the size of the area and roof access. Because it involves molten asphalt near 400 to 500 degrees and open kettles, it is a licensed contractor job rather than a DIY patch.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.