Roofing emulsion is a water-based bitumen coating that dries to a black, flexible, waterproof film over an existing roof. It is one of the cheapest liquid coatings sold, running roughly $9 to $15 a gallon, or about $1 to $2.50 per square foot installed as part of a system. It is a base coat and dampproofer, not a finished membrane, and the word points to two different products depending on which side of the Atlantic you buy it.
Applied correctly, emulsion can buy a tired built-up or modified bitumen roof another 5 to 10 years for a fraction of a tear-off. Sold as a standalone long-term membrane, it disappoints. This guide separates the two meanings of the term, gives real coverage and cost numbers, and names the jobs emulsion is actually built for. It sits alongside the rest of our roofing basics guides.
What is roofing emulsion?
Roofing emulsion is asphalt (bitumen) broken into tiny particles and suspended in water with an emulsifier, usually bentonite clay. It brushes, rolls, or sprays on cold, then cures as the water evaporates and the asphalt particles fuse into one continuous black film. Because it carries no solvents, it is low-odor, non-flammable while wet, and cleans up with plain water.
That water base is the whole story of the product. There is no torch and no kettle, so it is safer to apply than torch-on felt and produces no disruptive fumes over an occupied building. The trade-off is that the film only forms as the water leaves, so emulsion needs warm, dry weather to cure and can wash off if rain hits it too soon.
Fibered vs non-fibered emulsion: which one to use
Non-fibered emulsion is smooth and thin, used to prime a surface, dampproof it, or act as the base coat under an acrylic topcoat. Fibered emulsion has glass or mineral fibers mixed in for body, so it builds thicker in one pass and bridges hairline cracks. As a rule, non-fibered goes down first or under other coatings, and fibered is the repair or surfacing coat.
| Type | What is in it | Best for | Typical coverage per coat |
|---|---|---|---|
| Non-fibered | Asphalt, water, clay emulsifier, no fibers | Priming, dampproofing, saturating polyester fabric, base under acrylic | 2 to 3 gal per 100 sq ft |
| Fibered | Non-fibered base plus glass or mineral fibers | Top or repair coat, bridging small cracks, resurfacing alligatored built-up roofs | 3 to 5 gal per 100 sq ft |
What surfaces does roofing emulsion bond to?
Roofing emulsion bonds to most asphalt-based and porous flat-roof surfaces. It is designed for low-slope commercial and outbuilding roofs, not pitched shingle roofs. On single-ply membranes and metal it depends on the specific product and a compatible primer, so check the manufacturer’s data sheet before you coat one of those.
- Built-up roofs (BUR) and coal tar pitch: the classic use, especially for resurfacing weathered or alligatored surfaces. See our guide to built-up roof repair for where a coating fits versus a patch.
- Modified bitumen: as a seal or restoration coat over an aged cap sheet.
- Gravel and mineral-surfaced roofs: after loose gravel is removed or spudded and the surface is primed.
- Concrete and masonry: as a dampproofer on decks, parapets, and foundation walls.
- Metal: only with a compatible rust-inhibiting primer, and usually as a base under a reflective topcoat.
Where it does not belong: as the finish on a sloped asphalt shingle roof, on a roof that holds standing water, or anywhere you need a manufacturer membrane warranty. Emulsion is a coating, not a warrantied system on its own.
US asphalt emulsion vs UK roofing emulsion: same word, two products
The term hides a real gap in expectation. In the United States, asphalt emulsion means a professional cold-applied restoration coating for flat commercial roofs, often built into a reinforced three-course system. In the United Kingdom and Ireland, roofing emulsion or black bitumen emulsion usually means a cheap DIY dampproofer and felt-roof paint sold in small tubs. Same chemistry, very different job.
| Question | US asphalt emulsion | UK roofing emulsion |
|---|---|---|
| Typical buyer | Commercial roofer or building owner | DIY homeowner |
| Typical use | Restoring a flat BUR or mod-bit roof, often reinforced with polyester and topcoated | Painting a felt shed or garage roof, sealing damp brickwork |
| Sold as | 5-gallon pails, 55-gallon drums, bulk totes | 2.5 to 5 liter tubs |
| Realistic expectation | 5 to 10 years alone, 15 to 20 in a reinforced system | A few seasons of dampproofing, not a membrane |
How much does roofing emulsion cost?
Roofing emulsion is the budget option among liquid coatings. Material runs about $9 to $15 per gallon in 5-gallon pails, dropping toward $4 to $8 per gallon in 55-gallon drums. As an installed system on a flat roof, expect roughly $1 to $2.50 per square foot, or about $100 to $250 per roofing square (100 square feet), depending on reinforcement and number of coats.
| Item | Typical price |
|---|---|
| Non-fibered, 5-gallon pail | $45 to $70 ($9 to $14 per gallon) |
| Fibered, 5-gallon pail | $50 to $80 ($10 to $16 per gallon) |
| 55-gallon drum (bulk) | $4 to $8 per gallon |
| Material only, per coat | $0.30 to $0.80 per sq ft |
| Installed system (pro) | $1.00 to $2.50 per sq ft |
Asphalt-based products track crude and bitumen prices, so pail costs move year to year with the BLS producer price data we track. For how emulsion compares on cost and lifespan against silicone, acrylic, and polyurethane, see our roof coating types and cost breakdown.
How long does roofing emulsion last?
On its own, an asphalt emulsion coat generally lasts 5 to 10 years before it needs recoating. Built into a reinforced system, with polyester fabric embedded between coats and a reflective acrylic or aluminum topcoat, the same base can reach 15 to 20 years. The topcoat matters because bare black emulsion absorbs solar heat and breaks down under UV faster than a coated surface.
Two things shorten its life. First, ponding water can slowly re-emulsify a water-based coating, so emulsion is a poor pick on roofs that hold water. Second, thin single passes with no reinforcement wear through at seams and cracks. The extra cost of polyester and a topcoat is usually what separates a 6-year job from a 16-year one.
How to apply roofing emulsion
Application is straightforward but weather-dependent. The film only forms as water evaporates, so you need a dry surface, air and roof temperatures above about 50 degrees Fahrenheit, and a clear forecast with no rain for at least 24 to 48 hours. Rushing any of those steps is the most common way emulsion jobs fail.
- Clean and dry the roof. Remove dirt, loose gravel, moss, and failed coating. Let the surface dry fully.
- Prime if needed. On dusty, chalky, or metal surfaces, apply the manufacturer’s primer first.
- Apply the base coat. Brush, roll, or spray a non-fibered coat at the rated 2 to 3 gallons per 100 square feet.
- Embed reinforcement at stress points. Lay polyester fabric into wet emulsion over seams, cracks, and flashings, then coat over it.
- Apply the surfacing coat. Once the base is cured, add a fibered coat, or a reflective topcoat if the spec or local cool-roof code calls for one.
- Let it cure. Full cure takes days, not hours. Keep foot traffic and water off until it is hard and dry.
When roofing emulsion is the wrong choice
Emulsion is cheap for a reason, and there are roofs where it costs more than it saves. Reach for a different system when any of these apply.
- Ponding water: standing water can re-emulsify the coating. Fix drainage or choose silicone instead.
- Pitched shingle roofs: emulsion is not a shingle finish or a substitute for reroofing.
- You need a warranty membrane: emulsion alone rarely carries a long manufacturer warranty.
- Cold or wet weather: below 50 degrees or with rain due, it will not cure properly.
- You want a cool roof with no topcoat: bare emulsion is black and absorbs heat, so it needs a reflective topcoat to meet cool-roof rules.
For sealing small cracks and flashings rather than coating a whole roof, a trowel-grade product often works better. Our guide to roofing cement and mastic covers where those beat a brush-applied emulsion.
Frequently asked questions
What is roofing emulsion used for?
Roofing emulsion is used to waterproof and restore existing flat and low-slope roofs, mainly built-up, modified bitumen, and gravel surfaces. It seals a weathered roof, levels minor irregularities, and serves as a dampproofer on concrete and masonry. It works as a base coat under acrylic, or as a repair coat when it contains fibers. It is not a finish for pitched shingle roofs.
Is roofing emulsion waterproof?
Once fully cured, roofing emulsion dries to a waterproof black film. It is not waterproof while still wet, and it needs dry weather and temperatures above roughly 50 degrees Fahrenheit to cure. On roofs that hold standing water, a water-based emulsion can slowly re-emulsify over time, so it performs best on surfaces that drain properly and, ideally, under a protective topcoat.
What is the difference between fibered and non-fibered emulsion?
Non-fibered emulsion is smooth and thin, used for priming, dampproofing, and as a base coat under acrylic. Fibered emulsion adds glass or mineral fibers, so it builds thicker in one pass and bridges hairline cracks, which makes it the better surfacing or repair coat. Many restoration systems use both: non-fibered to prime and saturate fabric, fibered to surface.
How long does asphalt emulsion roof coating last?
Applied on its own, asphalt emulsion typically lasts 5 to 10 years before recoating. In a reinforced system, with polyester fabric embedded between coats and a reflective acrylic or aluminum topcoat, the base can last 15 to 20 years. Lifespan depends heavily on drainage, coating thickness, reinforcement, and whether a topcoat protects the black film from UV.
How much does roofing emulsion cost?
Roofing emulsion costs about $9 to $15 per gallon in 5-gallon pails, and roughly $4 to $8 per gallon bought in 55-gallon drums. As an installed system on a flat roof, expect about $1 to $2.50 per square foot, or $100 to $250 per roofing square. Reinforcement fabric and a reflective topcoat add cost but extend the life significantly.
Can you apply roofing emulsion over felt or a wet roof?
You can coat sound bitumen felt with emulsion once it is clean and dry, which is a common DIY use on shed and garage roofs. You cannot apply it to a wet roof or in the rain. Emulsion cures only as water evaporates, so a damp surface or rain within 24 to 48 hours can stop it curing or wash it off entirely.
Is roofing emulsion the same as roofing cement?
No. Roofing emulsion is a thin, brush or spray-applied coating that covers large areas and cures by water evaporation. Roofing cement, or mastic, is a thick trowel-grade paste used to seal specific cracks, seams, and flashings. Emulsion coats and dampproofs a whole roof, while cement patches localized problems. Many repairs use both, cement at details and emulsion across the field.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.