By The Roofing Brief Team. Last reviewed: October 2026.
Roof coating materials fall into four main chemistry families, acrylic, silicone, polyurethane, and asphalt based, plus the ancillary materials that turn a bucket of coating into a system: primer, reinforcing polyester fabric, mastic, and sometimes granules. The material you pick is driven less by price than by two things: the substrate it has to stick to, and whether the roof holds water longer than 48 hours, the ponding limit printed on APOC’s 241 acrylic data sheet. On current maker data sheets, volume solids run from about 43% for a water-based asphalt emulsion to 97% for a 100% silicone, and that one number sets how many gallons reach a given film thickness.
Pick the wrong chemistry for the deck and the coating peels, blisters, or washes off inside a season: APOC’s 301 asphalt emulsion sheet, for example, says not to use it on TPO, PVC, EPDM or Hypalon. The tables here match each material to the substrate it bonds to, using published data-sheet values. For the cost-per-square-foot decision between the four mainstream options, see the roof coating types and cost breakdown, and for more background browse our learn about roofing library.
What are roof coating materials made of?
A roof coating is a liquid-applied, fluid membrane that cures into a continuous elastomeric film over an existing roof. Every coating is built from three parts: a resin or binder (the chemistry that gives it its name), a carrier (water or solvent that evaporates), and pigments plus fillers for color, reflectivity, and body. Solids content, the percentage left on the roof after the carrier flashes off, is measured by volume under ASTM D2697: APOC 252 acrylic lists 54% by volume and 66% by weight, so a 12 lb gallon leaves well under a gallon of film.
Higher solids means more cured film per gallon and fewer coats to reach target thickness. APOC 576 silicone lists 97 ± 3% solids by volume, so it lays down thick fast. APOC 252 acrylic lists 54%, meaning close to half of each gallon evaporates. That difference decides how many gallons a job actually needs.
Roof coating formulas and chemical composition by product
| Product (chemistry) | Carrier | Solids by volume | Weight per gallon | VOC (regulatory) | Source |
|---|---|---|---|---|---|
| APOC 252 (acrylic elastomeric) | Water | 54% | 12 lb | <50 g/L | APOC 252 TDS |
| APOC 576 (100% silicone) | Low-solvent, moisture cure | 97 ± 3% | 11.05 lb | <10 g/L | APOC 576 TDS |
| AldoThane 386 (single-component aliphatic urethane) | Solvent, moisture cure | 88% | Not listed in this table | <240 g/L | AldoThane 386 data sheet |
| APOC 301 (asphalt emulsion) | Water | >43% | 8.76 lb | <10 g/L | APOC 301 TDS |
| APOC 202 (fibered asphalt cutback) | Solvent | Not listed | 8.5 to 9.0 lb | 300 g/L max | APOC 202 TDS |
The main roof coating material types
Four chemistries cover most coating work, and the Roof Coatings Manufacturers Association names the same four as the most common types: acrylic, silicone, polyurethane, and asphalt based. A handful of specialty materials (butyl, SEBS, polyurea) fill niche substrates. The table below sorts them by base chemistry, carrier, and the roof each one fits best. RCMA also publishes reference material for most of these categories. Our roof coating comparison lines up solids, elongation, ponding resistance and cost for all four.
| Material | Base chemistry | Carrier | Best-fit substrate | Main limit |
|---|---|---|---|---|
| Acrylic | Water-based acrylic resin | Water | Metal, mod-bit, concrete, single-ply | Erodes under standing water |
| Silicone | Moisture-cure silicone | High solids, low solvent | SPF foam, ponding flat roofs, single-ply | Holds dirt, hard to recoat |
| Polyurethane | Aromatic base, aliphatic top | Solvent | SPF, decks with foot traffic | Higher cost, odor during cure |
| Asphalt emulsion | Asphalt in water | Water | Mod-bit, BUR, metal | Not for single-ply, dark unless top-coated |
| Asphalt cutback | Asphalt in solvent | Solvent | BUR, mod-bit | Strong odor, flammable wet |
| Aluminized asphalt | Asphalt plus aluminum flake | Solvent | Metal, mod-bit, BUR | Reflectivity fades as flake oxidizes |
| Butyl | Butyl rubber | Solvent | EPDM, single-ply | Limited color, niche supply |
| SEBS | Styrene block copolymer | Solvent | Metal roofs | Metal-focused, narrow use |
| Polyurea | Two-part spray polyurea | Plural-component | Concrete, plaza decks | Needs trained applicator and rig |
Acrylic coatings
Acrylic is the default for reflective, cool-roof work on sloped commercial metal and mod-bit roofs. It is water-based, low odor, and available in white and tints with high initial solar reflectance: APOC lists 0.85 for 241 and 0.90 (ASTM C1549) for 252, with an SRI of 115, a range covered in our cool roof energy savings report. Acrylic conforms to ASTM D6083. Its weakness is standing water: prolonged ponding softens and re-emulsifies the film, so APOC’s 241 sheet requires drainage that does not hold water longer than 48 hours, and 252’s sheet disclaims liability where ponding may prevail.
Silicone coatings
Silicone is the ponding-water material. It cures by reacting with humidity, stays flexible for years, and erodes far slower than acrylic without turning brittle. At the 71 sq ft per gallon coverage on APOC’s 576 sheet, one gallon lays down about 22.6 wet mils, or about 21.9 dry mils at 97% volume solids, and ASTM D6694 covers silicone over spray polyurethane foam. The catch is recoating: almost nothing bonds to cured silicone except more silicone, so a future restoration is locked into the same chemistry or a full strip. See our deeper look at silicone roof coating and our ranking of the best silicone roof coatings.
Polyurethane coatings
Polyurethane coatings carry the best impact and foot-traffic resistance of the common materials, which is why they suit decks, walkways, and roofs that see service traffic. Systems usually pair an aromatic base coat for build and adhesion with an aliphatic top coat that resists UV yellowing. Moisture-cured polyurethane over foam follows ASTM D6947. The AldoThane 386 data sheet shows the gap in toughness: 1,500 psi tensile strength and 325% elongation (ASTM D2370), against 365 psi for APOC 252 acrylic. The tradeoffs are solvent odor during cure (AldoThane lists VOC under 240 g/L, against under 50 g/L for 252) and a higher material cost than acrylic.
Asphalt-based coatings
Asphalt coatings are the legacy material for asphalt roofs: modified bitumen, built-up (BUR), and metal. Asphalt emulsion is water-based and mixes asphalt with clay or bentonite; asphalt cutback thins asphalt with solvent for cold or wet adhesion. Both are dark and non-reflective unless finished with an aluminized or acrylic top coat: APOC allows a reflective coat 7 days after its 301 emulsion and recommends waiting at least 45 days after its 202 fibered cutback. Asphalt coatings should not go over TPO, EPDM, or PVC single-ply; the 301 sheet rules out TPO, PVC, EPDM and Hypalon by name.
Which roof coating material bonds to which substrate?
Substrate compatibility decides whether a coating stays bonded. A material that grips bare metal may peel off cured silicone or dissolve an EPDM membrane. The APOC sheets show how specific the rules get: 252 and 576 both require rusty metal to be wire-brushed and primed with APOC 291, 576 suggests APOC 583 as a stain-blocking base over asphalt, and 252 asks for one summer season of cure before going over aluminum, asphalt or tar coatings. Use the matrix below as a first filter, then confirm against the maker’s data sheet.
| Substrate | Acrylic | Silicone | Polyurethane | Asphalt-based |
|---|---|---|---|---|
| Metal (galvanized, Galvalume) | Yes, primer often needed | Yes, with primer | Yes | Yes (aluminized) |
| SPF (spray foam) | Yes | Yes (D6694) | Yes (D6947) | Not recommended |
| Modified bitumen / BUR | Yes | Yes, with primer | Yes | Yes |
| TPO | Limited, needs primer | Yes, with primer | Yes | No |
| EPDM | With butyl primer | Yes, with primer | Limited | No |
| PVC | Limited, needs primer | Yes, with primer | Yes | No |
| Concrete | Yes | Yes | Yes | Yes |
| Asphalt shingles | Rarely, warranty risk | Not recommended | No | Limited, bleed-through |
Coating asphalt shingles is a separate question with its own tradeoffs: APOC’s 241 sheet says plainly “Do not use on shingle roofs,” and coating can conflict with a shingle maker’s warranty. Single-ply membranes can be coated to extend service life, but APOC 576 lists only aged TPO and aged EPDM, and single-ply jobs usually need a membrane-specific primer and a clean, sound surface first.
The full coating system: it is more than the bucket
A roof coating material rarely performs alone. APOC’s 252 sheet, for example, calls for one coat over all seams and joints, a one-hour cure, then two full coats over the whole roof, with leaks and cracks first repaired with polyester reinforcing fabric and APOC 264 roof cement. A typical restoration system stacks up in this order:
- Primer: a thin bonding layer matched to the substrate, such as APOC 291 on wire-brushed rusty metal. Weathered single-ply and cured silicone each need a different primer, or none, per the data sheet.
- Base coat: the first full-thickness pass that builds the membrane and carries most of the dry mils.
- Reinforcing fabric: polyester or fiberglass mesh embedded in wet coating over seams, penetrations, and flashings to bridge movement and add tensile strength.
- Mastic or sealant: a thick trowel-grade version of the coating used to detail drains, curbs, and fastener heads before the field coats go down.
- Top coat: the second full pass that reaches target thickness and delivers the final color and reflectivity.
- Granules (optional): broadcast into a wet top coat on walkways or for a granulated finish and added UV and foot-traffic protection.
How thick, how much: mils, coverage, and solids
Coating performance is measured in dry mils, the film thickness left after curing, not in gallons poured. Most manufacturer warranties tie their term directly to a minimum dry-mil thickness, so hitting the number is what protects the roof and the warranty. One US gallon spread over 1 sq ft is 1,604 wet mils thick (231 cubic inches over 144 square inches), so wet mils = 1,604 ÷ sq ft per gallon, and dry mils = wet mils × volume solids. The data sheets below land between about 20 and 35 dry mils for a full system.
Coverage runs roughly 1 to 1.5 gallons per 100 square feet per coat for a mid-20s mil target, though it varies with surface texture and solids content. A porous, granulated mod-bit roof drinks more material than smooth metal. Because water-based acrylic loses close to half its volume to evaporation, it usually needs more gallons than high-solids silicone to reach the same dry thickness. Our roof coating mil thickness chart runs that math by volume solids.
Worked example: wet to dry mils from the data sheets
| Product | Maker coverage | Wet mils | Volume solids | Dry mils | Source |
|---|---|---|---|---|---|
| APOC 252 acrylic, 2 coats | 1.5 gal per 100 sq ft per coat (3 gal total) | 24.1 per coat | 54% | 13.0 per coat, 26.0 total | APOC 252 TDS |
| APOC 576 silicone | About 71 sq ft per gal | 22.6 | 97% | 21.9 | APOC 576 TDS |
| AldoThane 386 urethane, 2 coats | 20 wet mils per coat (about 2.5 gal per 100 sq ft total) | 40 total | 88% | 35.2 total | AldoThane 386 data sheet |
| APOC 301 asphalt emulsion, 2 coats | About 350 sq ft per 5 gal per coat | 22.9 per coat | >43% | Over 9.9 per coat, over 19.7 total | APOC 301 TDS |
Dry mils are calculated here from each maker’s coverage and volume solids; real film thickness drops on rough or porous surfaces, which absorb extra material, so check with a wet-mil gauge during application; APOC 202, for example, needs 1.0 to 1.5 gallons per 100 sq ft on concrete against 1.0 on smooth built-up roofs.
Roof coating material properties from named data sheets
| Property | APOC 252 acrylic | APOC 576 silicone | AldoThane 386 urethane | Source |
|---|---|---|---|---|
| Tensile strength | 365 psi (ASTM D2370) | 250 psi | 1,500 psi (ASTM D2370) | Maker data sheets |
| Elongation | 463% initial, 131% after weathering | 315% | 325% | Maker data sheets |
| Initial solar reflectance | 0.90 (ASTM C1549) | 90 ± 1% | 81% (white) | Maker data sheets; check the CRRC directory for rated values |
| SRI (initial) | 115 | 115 | 101 (white) | Maker data sheets |
| Vapor permeability | <15 perms (ASTM D1653) | 3 perms | Not listed | Maker data sheets |
| Reference specification | ASTM D6083 | ASTM D6694 | Single-component moisture-cure urethane (ASTM D6947 covers this class over SPF) | ASTM |
Elongation and tensile values from ASTM D2370 and ASTM D412 are not interchangeable, so compare products only when the sheets cite the same method; APOC’s 576 sheet does not name its test method for those two values.
| Property | Acrylic | Silicone | Polyurethane |
|---|---|---|---|
| Solids by volume (named examples) | 54% (APOC 252) | 97% (APOC 576) | 88% (AldoThane 386) |
| Ponding-water tolerance | Low | High | Moderate to high |
| Foot-traffic resistance | Moderate | Low (slick when wet) | High |
| Recoat friendliness | Easy | Hard (silicone only) | Moderate |
| Reference spec | ASTM D6083 | ASTM D6694 | ASTM D6947 |
How to choose the right roof coating material
Match the material to the roof’s biggest problem, then confirm substrate compatibility and cost. The first test is the 48-hour drainage rule; the other thresholds in this table come from the data sheets and ASTM standards cited above.
| If the roof | Choose | Threshold or rule |
|---|---|---|
| Holds water longer than 48 hours after rain | Silicone | APOC 241 acrylic requires drainage within 48 hours; APOC 576 silicone is sold for ponding areas |
| Drains within 48 hours and needs maximum reflectance | White acrylic or silicone | 0.85 to 0.90 initial reflectance on the APOC 241, 252 and 576 sheets |
| Carries foot traffic or service carts | Polyurethane | 1,500 psi tensile (AldoThane 386) vs 250 to 365 psi for the silicone and acrylic examples |
| Is BUR or mod-bit on a tight budget | Asphalt emulsion, then a reflective top coat | Reflective coat 7 days after APOC 301; 45 days after APOC 202 |
| Is single-ply (TPO, PVC, EPDM) | Silicone or acrylic with the maker’s primer; never asphalt | APOC 301 excludes all single-ply; APOC 576 lists aged TPO and EPDM only |
| Is asphalt shingle | Usually no coating | APOC 241: “Do not use on shingle roofs” |
| Is spray polyurethane foam | Silicone or urethane | ASTM D6694 and ASTM D6947 are written for coatings over SPF |
- Ponding or slow drainage: silicone, which shrugs off standing water where acrylic erodes.
- Reflectivity and energy savings: bright-white acrylic or silicone; APOC lists 0.90 initial reflectance for both 252 and 576, and the Cool Roof Rating Council directory publishes rated initial and 3-year values.
- Foot traffic or impact: polyurethane, or a polyurethane top coat with broadcast granules.
- Asphalt roof on a budget: asphalt emulsion, ideally finished with a reflective top coat.
- Spray foam roof: silicone or polyurethane, the two chemistries written into the SPF coating standards.
Whatever the chemistry, the coating only performs if the roof underneath is sound and the drainage works. Every APOC sheet cited here requires a clean, dry surface, and 301 says not to apply if rain is expected within 24 to 48 hours. Coating is a restoration tool for a roof with life left, not a fix for a wet, failing deck: wet insulation found by a moisture survey has to be cut out and replaced first, and when saturation is widespread or the deck is compromised, compare the coating cost with replacement.
Frequently asked questions
What are the different types of roof coating materials?
The four main roof coating materials are acrylic (water-based, reflective, best for draining roofs), silicone (high solids, best for ponding water and spray foam), polyurethane (toughest against foot traffic), and asphalt based (emulsion or cutback for asphalt roofs), the same four the Roof Coatings Manufacturers Association lists as most common. Specialty materials include butyl for EPDM, SEBS for metal, and two-part polyurea for concrete decks.
What roof coating material is best for a flat roof with ponding water?
Silicone is the standard choice for flat roofs that hold standing water. APOC 576, for example, is sold for areas where ponding may occur, while APOC’s 241 acrylic sheet requires drainage within 48 hours. The tradeoff is that cured silicone is slick when wet and can only be recoated with more silicone, so future restorations are locked to that chemistry.
Do roof coatings need a primer?
Often yes, depending on the substrate. APOC’s 252 and 576 sheets both require rusty metal to be wire-brushed and primed with APOC 291, and weathered single-ply membranes like TPO and PVC, and cured silicone, usually need a substrate-specific primer too. The manufacturer data sheet is the authority: applying the wrong primer, or none where one is required, is a leading cause of early peeling.
What is elastomeric roof coating made of?
Elastomeric means the cured film stretches and returns without cracking: APOC 252 acrylic lists 463% elongation and APOC 576 silicone 315%. Most elastomeric coatings are acrylic or silicone, made of a resin binder, a carrier (water or low solvent) that evaporates, and pigments plus fillers for color and reflectivity. The elastomeric property lets the membrane flex with a roof that expands and contracts through daily temperature swings.
Can you coat any type of roof?
Most low-slope commercial roofs can be coated: metal, modified bitumen, built-up, spray foam, concrete, and single-ply with the right primer. Asphalt shingles are the main exception; APOC’s 241 sheet says not to use it on shingle roofs, and coating can conflict with a shingle warranty. The roof must also be structurally sound and dry, because coating a saturated or failing deck traps moisture rather than fixing the leak.
How many coats of roof coating do you need?
Most restoration systems use at least two coats, a base coat and a top coat, plus reinforcing fabric at seams and penetrations. APOC 252 acrylic, for example, needs two coats at 1.5 gallons per 100 sq ft each, about 26 dry mils in total, while AldoThane 386 urethane allows two coats at 20 wet mils or one at 32. Warranty terms are tied to the final dry-mil thickness, not the number of coats.