Roofing cement is a thick, asphalt-based paste used to seal leaks, patch cracks, and bond flashing on a roof. Most products sold as roofing cement are asphalt cutback cements meeting ASTM D4586, trowel-applied at about 1/8 inch thick, and cure in 24 to 48 hours. It is a repair material, not a roofing system: it buys time on a leak or holds a patch, but it does not replace proper flashing, underlayment, or new shingles. Homeowners reach for it because one $15 tub fixes a dozen small problems.
What is roofing cement?
Roofing cement is a trowel-grade compound of asphalt, mineral fillers, and reinforcing fibers, thinned with a petroleum solvent so it stays workable in a tub. It sets by solvent evaporation, gripping shingles, metal, masonry, and most membranes. The generic product is often labeled “plastic roof cement” or “flashing cement,” and quality grades reference ASTM D4586 (asbestos-free asphalt roof cement).
The nickname “the duct tape of roofing” fits: it is cheap, sticky, and forgiving. It is also frequently misused as a permanent fix, which is how a $15 patch turns into a $600 decking repair a year later. Treat it as a bandage, not a cure.
Types of roofing cement and roof sealant cement
There are five common formulations, and picking the wrong one is the most common mistake. Asphalt (plastic) roof cement handles most shingle and flashing repairs. Wet patch roofing cement bonds to damp surfaces for emergencies. Fibered, butyl, and silicone variants trade cost for flexibility or membrane compatibility. The table below maps each to its job.
| Type | Base | Best for | Typical cost (2026) | Watch out for |
|---|---|---|---|---|
| Plastic (asphalt) roof cement | Asphalt cutback, fibered | Shingle cracks, flashing beds, nail heads | $12 to $22 per gallon | Dry surface only unless labeled wet |
| Wet patch roofing cement | Asphalt emulsion or wet-grade cutback | Active leaks, damp or rained-on surfaces | $15 to $28 per gallon | Lower long-term adhesion than dry-set |
| Fibered / roofing tar cement | Asphalt with glass or cellulose fiber | Larger holes, seams, bridging gaps | $14 to $25 per gallon | Cracks if applied too thick |
| Butyl roof cement | Butyl rubber blend | Metal roofs, joints that move | $20 to $40 per gallon | Costlier, slower cure |
| Silicone / polyurethane sealant cement | Silicone or urethane | Flat/low-slope, UV exposure, ponding | $25 to $60 per gallon | Poor adhesion over old asphalt cement |
Asphalt-based cement should not be applied over EPDM, TPO, or PVC single-ply membranes: the solvents degrade the sheet. For those roofs, use a manufacturer-matched sealant or the compatible seam product. Our EPDM rubber membrane pricing guide covers what actually bonds to rubber. On standing-seam and corrugated panels, a purpose-made product beats asphalt cement; our guide to metal roofing sealant types and how to pick one explains why.
What is roofing cement used for?
Roofing cement seals penetrations and patches small breaches. The five jobs it does well are sealing around flashing, chimneys, and vents; re-bedding lifted shingle tabs; filling nail-hole and hairline cracks; bridging small membrane splits on low-slope roofs; and gluing down loose ridge caps. Each is a spot repair measured in inches, not a coating for the whole roof.
- Flashing seals: a bead behind step or counter flashing stops the wall-to-roof junction from wicking water. It backs up metal, it does not replace it.
- Vent and pipe boots: a ring around a cracked boot buys a season, but the boot itself is the fix. Roughly 30% of roof leaks trace to failed pipe boots.
- Shingle cracks and lifted tabs: a dab under the tab and a smear over the crack, pressed flat, reseals wind-loosened shingles.
- Emergency leak patch: troweled over a tarp seam or split, wet-patch grade holds through a storm until a real repair.
What it is not for: sealing whole valleys, coating an aging roof to “extend” it, or standing in for flashing on a new install. Those uses fail because cement is rigid once cured and cracks as the roof moves. When the problem is a leak with an unknown source, start with our roof leak repair guide to find it before you seal blind.
How to apply roofing cement
Apply roofing cement to a clean, dry surface with a trowel or putty knife, spread about 1/8 inch thick, work bottom to top on vertical surfaces, and let it cure 24 to 48 hours. Thickness is the detail most people get wrong: piling it on does not make a stronger seal, it makes one that skins over on top and stays soft underneath, then cracks. Thin, pressed, and feathered at the edges lasts longer.
- Clean the area. Remove debris, granules, old failed cement, and loose material. Adhesion is only as good as the surface under it.
- Dry it (or buy wet-grade). Standard cement needs a dry substrate. If the surface is damp and the leak is active, use wet patch roofing cement rated for it.
- Load the trowel. Scoop a golf-ball amount. Work small; the solvent flashes off and the tub skins over if you leave it open.
- Spread at 1/8 inch. Fill the crack or hole, then feather the cement 2 to 3 inches past the edge so water cannot track under the patch.
- Embed reinforcement for larger patches. For holes over an inch, press fiberglass mesh into a first coat, then cover with a second. This is how fibered cement bridges a gap without sagging.
- Work bottom to top on vertical faces. Around chimneys and walls, this keeps the cement from sliding and shingles the overlaps against gravity.
- Cure before rain. Skin time is often 2 to 4 hours; full cure is 24 to 48 hours depending on temperature and thickness. Check the label; most asphalt cements want application above 40°F.
For flashing work specifically, cement is the backup bead, not the seal itself. Get the metal detail right first: our guide to roof flashing types and installation shows where each piece goes and why flashing, not cement, is what stops most leaks.
Roofing cement vs roof sealant vs roofing tar
These three terms get used interchangeably but describe different products. Roofing cement is a thick trowel-grade asphalt paste for patching. Roof sealant is a thinner gun-applied caulk (often silicone or polyurethane) for narrow joints. Roofing tar is molten or emulsified asphalt used mostly on built-up flat roofs. The table sorts them.
| Product | Consistency | Applied with | Best joint width | Flexibility once cured |
|---|---|---|---|---|
| Roofing cement | Thick paste | Trowel / putty knife | Gaps, holes, wide beds | Low, becomes rigid |
| Roof sealant | Gun-grade caulk | Caulk gun | Narrow seams under 1/4 inch | High, stays elastic |
| Roofing tar (mastic) | Heavy liquid | Mop, brush, or trowel | Full-surface built-up work | Low, brittle in cold |
Rule of thumb: if the gap moves or is narrow, use an elastic sealant; if it is a hole or a bed for flashing, use cement; if you are laying or repairing a built-up flat roof, that is tar or mastic territory. Silicone sealant does not bond well over cured asphalt cement, so do not layer one on the other.
When roofing cement fails (and what to do instead)
Roofing cement fails when it is used as a permanent fix, applied too thick, put over an incompatible membrane, or asked to seal a joint that flexes. Cured asphalt cement is rigid, so a roof that expands, contracts, and vibrates in wind eventually opens hairline cracks in the patch, and the leak returns. Sun accelerates this: unprotected asphalt cement chalks and cracks under UV within a few seasons.
The honest limit: a cement patch on a shingle roof may last 1 to 3 years; on a moving metal seam or a membrane, far less. If you are re-cementing the same spot each year, the underlying flashing, boot, or shingle has failed and needs replacing, not re-sealing. A patch that keeps leaking is often the cheapest early warning that the real repair is overdue.
Roofing cement: frequently asked questions
What is roofing cement used for?
Roofing cement seals and patches small roof problems: it beds flashing around chimneys and vents, reseals lifted or cracked shingles, fills nail holes and hairline cracks, and bridges small splits on low-slope roofs. It is a spot repair material measured in inches, not a coating for a whole roof, and it backs up flashing rather than replacing it.
What is the difference between plastic roof cement and wet patch roofing cement?
Plastic (asphalt) roof cement is the standard fibered paste for dry-surface repairs like shingle cracks and flashing beds. Wet patch roofing cement uses a formula that bonds to damp or rained-on surfaces, making it the choice for active leaks and storm emergencies. Wet-grade trades some long-term adhesion for the ability to stick when the roof cannot be dried first.
How long does roofing cement take to dry?
Roofing cement usually skins over in 2 to 4 hours and reaches full cure in 24 to 48 hours, depending on temperature and how thick it was applied. Most asphalt cements need application above 40°F. Applying it too thick traps solvent underneath, so the surface skins while the interior stays soft and later cracks.
Is roofing cement a permanent fix?
No. Roofing cement is a temporary repair. Cured asphalt cement is rigid and cracks as the roof moves and heats, so a patch on a shingle roof may last 1 to 3 years and far less on flexing metal seams or membranes. If you re-cement the same spot yearly, the underlying flashing, boot, or shingle has failed and needs replacing.
Can you put roofing cement on a wet roof?
Only with wet patch roofing cement, which is formulated to bond to damp surfaces. Standard plastic roof cement needs a clean, dry substrate and will not adhere reliably to a wet roof. For an active leak during rain, a wet-grade product troweled over the split holds through the storm until a proper dry repair can be made.
Can I use roofing cement on a rubber or TPO membrane?
No. The solvents in asphalt roofing cement degrade single-ply membranes like EPDM, TPO, and PVC. Use a manufacturer-matched sealant or the compatible seam product for those roofs. Applying asphalt cement to a rubber or thermoplastic membrane can shorten its life and void the membrane warranty.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.