Roofing Cement: What It Is, Types, Uses & Pro Application Tips

Walk into any roofing supply shop and you’ll find rows of heavy cans labeled “roofing cement,” “plastic cement,” or “wet patch.” For professional roofers, this thick, tar-like material is a go-to problem solver — used to seal flashing, bed shingles, and patch leaks. But roofing cement is also one of the most misunderstood products in roofing: incredibly useful in the right hands, and a recipe for bigger problems when misused.

In this guide, the GAF Certified roofers at Zuniga Roofing Inc. break down what roofing cement is, the different types, where it works (and where it doesn’t), how pros apply it, and when a DIY patch is fine versus when you should call a professional in Waukegan, Beach Park, or anywhere in Lake County and the greater Chicago area.

What Is Roofing Cement?

Roofing cement — also called asphalt plastic cement or mastic — is a thick, trowel-grade compound made from asphalt, mineral fillers, and fibers, blended with solvents that keep it workable until it cures. It comes in cans or tubes and has the consistency of very thick peanut butter. Once applied and exposed to air, the solvents evaporate and the cement hardens into a tough, water-resistant seal.

Unlike caulk, roofing cement is specifically formulated to bond to roofing materials: asphalt shingles, modified bitumen, metal flashing, masonry, and even damp surfaces (in the case of “wet patch” formulas). It stays slightly flexible after curing, which lets it move with the roof through Illinois’s dramatic temperature swings without cracking apart immediately.

Think of roofing cement as the duct tape of the roofing world — an incredibly handy repair material, but not a substitute for proper roofing components. A glob of cement can stop a leak today, but it can’t replace failed flashing or a worn-out shingle forever.

Types of Roofing Cement

Not all roofing cements are the same. Using the wrong type is one of the most common DIY mistakes. Here are the main categories you’ll encounter:

Asphalt Plastic Cement (General Purpose)

The standard trowel-grade cement. Used for sealing shingle tabs, bedding flashing, repairing blisters on flat roofs, and general patching. It’s the most versatile option and the one pros reach for most often. It must be applied to clean, dry surfaces for the best bond.

Wet-Surface / Wet Patch Cement

Specially formulated to adhere to damp or even wet surfaces — a lifesaver during emergency leak situations when you can’t wait for the roof to dry. Every roofer’s truck in Lake County carries wet patch during storm season, because leaks rarely schedule themselves for sunny days. If you’re dealing with active water intrusion right now, our emergency roof repair team uses professional-grade wet-surface products to stop the damage fast.

Flashing Cement

A heavier-bodied cement designed specifically for sealing and bedding metal flashing around chimneys, skylights, vents, and wall junctions. It typically contains more reinforcing fibers for extra strength at these high-stress transition points.

Rubberized / Polymer-Modified Cement

Enhanced with rubber polymers for superior flexibility and adhesion. These premium cements handle expansion and contraction better than basic asphalt cement, making them a smart choice for Illinois roofs that cycle between sub-zero winters and hot summers. They also tend to resist UV breakdown longer.

Comparing Roofing Cement Types

Type	Best For	Can Apply Wet?	Key Strength
Asphalt plastic cement	General repairs, shingle tabs	No	Versatile and affordable
Wet-surface / wet patch	Emergency leak stops	Yes	Bonds in wet conditions
Flashing cement	Chimneys, skylights, vents	No	Fiber-reinforced for high-stress joints
Rubberized / polymer-modified	Long-lasting repairs	Varies	Superior flexibility and UV resistance

Common Uses of Roofing Cement

Here’s where roofing cement earns its keep on real roofs:

• Sealing flashing: Bedding and sealing step flashing, counter flashing, and vent flashing where they meet shingles or masonry. This is the number one legitimate use.
• Securing shingles: Dabbing down lifted shingle tabs or wind-damaged shingles as a temporary or supplemental hold (proper nailing is still required).
• Patching small leaks: Troweling over cracks, punctures, and pinholes in flat roofing membranes or shingle surfaces as a stopgap repair.
• Sealing pipe boots and vents: Reinforcing the seal around plumbing vent flashings whose rubber boots have cracked with age — one of the most common leak sources we find during roof leak detection inspections in Waukegan.
• Repairing blisters and seams: Cutting open, drying, and resealing blisters on modified bitumen or built-up flat roofs.

How Professionals Apply Roofing Cement

Proper application is the difference between a repair that lasts years and one that fails by spring. Here’s how our crews do it:

• 1. Diagnose first. Never just smear cement over a stain. We trace the leak to its true entry point — water often travels several feet from where it shows up inside.
• 2. Prep the surface. Remove loose material, dirt, and debris. For the strongest bond, the surface should be clean and dry (unless using wet-patch formula). Pros often prime dusty or porous surfaces first.
• 3. Apply at the right temperature. Most cements apply best between about 40°F and 100°F. In cold Lake County weather, pros warm the cans so the cement spreads properly instead of tearing the shingles.
• 4. Trowel, don’t glob. Apply in smooth, even layers about 1/8-inch thick, feathering the edges. Thick globs crack as they cure; thin, well-feathered applications flex and last.
• 5. Reinforce when needed. For larger patches, we embed fiberglass or polyester reinforcing mesh into the wet cement — creating a much stronger, longer-lasting repair.
• 6. Address the root cause. Cement over failed flashing without fixing the flashing is just a countdown to the next leak. Real repairs fix the underlying problem.

DIY vs. Hiring a Professional

A small tube of roofing cement from the hardware store can handle minor fixes — but know the limits.

Situation	DIY With Roofing Cement?	Call a Pro?
One lifted shingle tab after a windstorm	Reasonable, if you’re comfortable on a ladder	If the roof is steep or two stories
Small, visible crack around a vent	Possible as a temporary seal	Recommended — the boot may need replacement
Active leak during a storm	Emergency wet-patch only, from inside the attic if possible	Yes — call for emergency repair
Multiple leaks or widespread sealant failure	No — symptom of a bigger problem	Yes — needs professional diagnosis
Anything involving flashing replacement	Not recommended	Yes — flashing is a skilled trade

Limitations of Roofing Cement

Honest talk: roofing cement has real limits every homeowner should understand.

• It’s not permanent. Even the best cement application is a repair, not a restoration. UV exposure gradually breaks down asphalt-based cement, so exposed applications typically need attention within a few years.
• More is not better. The infamous “tar blob” — a giant mound of cement slapped over a problem — actually traps water underneath and makes proper repair harder later. We remove these regularly.
• It can’t fix structural issues. Rotted decking, failed flashing systems, and worn-out shingles need real replacement, not a coating of mastic.
• Wrong product, wrong place. Standard cement on a wet surface, or interior caulk on a roof, will fail quickly. Matching the product to the conditions matters.
• It can void warranties. Slathering cement over a relatively new roof can complicate manufacturer warranty claims. When in doubt, call the contractor who installed it.

When to Call a Roofer in Waukegan or Lake County

Call a professional when the leak is active, the source isn’t obvious, flashing is involved, the roof is steep or high, or you’ve already tried a DIY patch and it didn’t hold. Water damage compounds fast — what starts as a $200 flashing repair becomes a $2,000 drywall, insulation, and decking job if ignored through a rainy season.

Zuniga Roofing Inc. serves Waukegan, Beach Park, Zion, Gurnee, North Chicago, and the greater Chicago area with honest inspections and lasting repairs. If water is coming in right now, don’t wait — our emergency roof repair team responds quickly to stop the damage, and our roof leak detection service pinpoints hidden entry points other contractors miss.

Frequently Asked Questions About Roofing Cement

How long does roofing cement last?

It varies widely with product quality, application, and exposure. A properly applied, reinforced patch in a sheltered spot can last several years; exposed cement in harsh sun may start cracking within a couple of years. Think of it as a repair material with a finite lifespan, not a permanent roofing system.

Can roofing cement stop a leak in the rain?

Wet-surface (wet patch) formulas are designed exactly for this — they bond to damp surfaces and can stop active drips as an emergency measure. Standard asphalt cement won’t adhere well to wet surfaces. Either way, treat it as a stopgap until a permanent repair can be made in dry conditions.

Is roofing cement the same as tar?

Not exactly, though the terms get mixed up. Traditional coal tar is rarely used on residential roofs today. Modern “roofing cement” is asphalt-based plastic cement — refined, fiber-reinforced, and formulated specifically for roofing repairs. It outperforms old-fashioned tar in flexibility and UV resistance.

Can I use roofing cement on shingles?

Yes, for specific purposes: sealing down lifted tabs, sealing around flashing, and small patch repairs. But never use it as a substitute for proper nailing, and avoid coating large shingle areas — it traps moisture, looks terrible, and shortens shingle life.

Why do roofers say not to just “tar over” a leak?

Because surface patches rarely address the true entry point. Water travels — the stain on your ceiling is often feet away from the actual breach. Pros diagnose the source (failed flashing, cracked boot, nail pops) and fix that, using cement as a sealing component of a proper repair rather than a cover-up.

Lap Sealant for RV Roofs

If you own an RV, travel trailer, or camper, you have seen the white, rubbery beads tracing the roof’s edges, vents, and skylights. That is lap sealant — a self-leveling sealant made for RV roof repair and maintenance — and it is not the same product as roofing cement.

Lap sealant vs. roofing cement: roofing cement is asphalt-based, and its petroleum solvents can soften or damage EPDM and TPO rubber membranes — what most RV roofs are made of. Lap sealant is formulated for rubber and fiberglass RV roofs. It flows from the tube and self-levels into a smooth, domed bead that seals seams, screw heads, roof edges, and vent flanges without attacking the membrane underneath.

When to use it: reseal whenever you spot cracked, lifted, or gapped sealant around roof penetrations, or after replacing a vent or skylight. Lap sealant is a maintenance product, not a structural repair — if the membrane is torn or the decking feels soft, the roof needs professional attention.

Surface prep and application: wash the area, wipe it down with mineral spirits or denatured alcohol, and let it dry. Scrape off loose or flaking old sealant, but leave well-adhered beads in place — lap sealant bonds to itself. Apply in dry weather when temperatures are above about 50°F, run a steady bead with a caulk gun, and let it self-level; a slightly raised bead sheds water better than a tooled-flat one.

Resealing frequency: inspect your RV roof sealant at least twice a year — before and after travel season — and after hailstorms or low-branch strikes. Plan on touch-ups roughly once a year. UV exposure slowly breaks sealant down, and catching hairline cracks early is far cheaper than repairing water damage inside the walls.

Unsure whether a cracked seam is a quick reseal or a bigger issue? Call Zuniga Roofing Inc. at (858) 399-8124 for honest advice and a free inspection.