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Which coating goes on my flat roof?

Three questions. We'll tell you what works on your roof, what needs a primer first, and what will peel. It's based on manufacturer data sheets, not on what's on sale.

Compatibility at a glance

Rows are what's on the roof now. "Primer" means it works with the right primer or prep; "Caution" means practice varies, so read the note and the data sheet.

Roof nowSiliconeAcrylic (elastomeric)Polyurethane (urethane)SEBS (synthetic rubber)Fibered aluminumAsphalt emulsion
Modified bitumen Works with the right primer/prepWorks with the right primer/prepPossible, with caveatsWorks with the right primer/prepGood matchGood match
Built-up roof (tar and gravel) Works with the right primer/prepWorks with the right primer/prepPossible, with caveatsPossible, with caveatsGood matchGood match
Rolled roofing Works with the right primer/prepGood matchPossible, with caveatsPossible, with caveatsGood matchGood match
TPO single-ply Works with the right primer/prepWorks with the right primer/prepPossible, with caveatsWorks with the right primer/prepDon'tDon't
PVC single-ply Possible, with caveatsWorks with the right primer/prepPossible, with caveatsPossible, with caveatsDon'tDon't
EPDM rubber Works with the right primer/prepPossible, with caveatsPossible, with caveatsWorks with the right primer/prepDon'tDon't
Spray polyurethane foam Good matchGood matchGood matchPossible, with caveatsDon'tDon't
Low-slope metal Works with the right primer/prepWorks with the right primer/prepWorks with the right primer/prepGood matchGood matchPossible, with caveats
Already coated: silicone Good matchDon'tDon'tDon'tDon'tDon't
Already coated: acrylic Good matchGood matchPossible, with caveatsPossible, with caveatsDon'tDon't
Read every note

Modified bitumen

Rolls about 3 feet wide with overlapping seams where a little black asphalt squeezed out; the surface is usually covered in granules, sometimes smooth. Asphalt-based. Granulated cap sheets take coatings well; smooth sheets and new asphalt need a primer or weathering time to stop bleed-through.

  • Silicone: Works with the right primer/prep. Use a bleed-blocking primer over asphalt so the white topcoat doesn’t stain, and let new mod bit weather at least 30 days first.
  • Acrylic (elastomeric): Works with the right primer/prep. Granulated cap sheets often need no primer, but smooth SBS/APP sheets do, and fresh asphalt or roof cement should weather 30 days to a full summer first.
  • Polyurethane (urethane): Possible, with caveats. Pro urethane systems are approved over mod bit, but they need specific primers and trained applicators; not a homeowner match.
  • SEBS (synthetic rubber): Works with the right primer/prep. SEBS systems such as IKO’s are made for granulated mod bit, applied over the maker’s own primer.
  • Fibered aluminum: Good match. An asphalt-based aluminum coating is compatible with mod bit; granulated surfaces use more per square foot.
  • Asphalt emulsion: Good match. Compatible as a resaturant or base coat on smooth or granulated mod bit, but it is black and adds no heat reflection.

Built-up roof (tar and gravel)

A thick, layered black roof with gravel embedded in it, or a smooth black or aluminum-coated surface with no visible seams. Gravel must be removed before most coatings. Older BURs may be coal-tar pitch rather than asphalt, and asphalt cements are not compatible with coal tar, so identify it first.

  • Silicone: Works with the right primer/prep. Loose and embedded gravel must be removed first, then a bleed-blocking primer; wet insulation is common on old BURs, so survey before coating.
  • Acrylic (elastomeric): Works with the right primer/prep. Remove gravel, prime smooth or hot-mopped asphalt (Henry calls for asphalt emulsion first), and expect a heavy base coat with fabric on rough surfaces.
  • Polyurethane (urethane): Possible, with caveats. Some urethane systems list smooth BUR, but gravel removal, primers and pro application make it a contractor decision.
  • SEBS (synthetic rubber): Possible, with caveats. SEBS makers list BUR as a secondary substrate; gravel must go and the right primer is required.
  • Fibered aluminum: Good match. The traditional BUR finish, on smooth-surfaced BUR only; Henry excludes roofs with loose or embedded gravel.
  • Asphalt emulsion: Good match. Works on smooth asphalt BUR; confirm it isn’t coal-tar pitch, which asphalt products are not compatible with.

Rolled roofing

Thin, shingle-like mineral-surfaced strips about 3 feet wide, usually nailed with lap cement at the seams; common on sheds, porches and low additions. Asphalt-based and thinner than modified bitumen. Mineral surfaces soak up more coating than smooth ones.

  • Silicone: Works with the right primer/prep. Like any asphalt roof, use a bleed-blocking primer and seal exposed nail heads and laps before coating.
  • Acrylic (elastomeric): Good match. Henry lists mineral-surfaced roofing with no primer needed, but expect 2–3 gal per 100 sq ft on rough granules and let new roll roofing weather first.
  • Polyurethane (urethane): Possible, with caveats. Possible in a pro system, but rarely worth the cost on thin roll roofing that is near the end of its life.
  • SEBS (synthetic rubber): Possible, with caveats. SEBS is sold for granulated modified bitumen; confirm the maker lists standard roll roofing before using it.
  • Fibered aluminum: Good match. Henry lists prepared roll roofing as a fibered-aluminum surface; avoid areas that pond.
  • Asphalt emulsion: Good match. Compatible as a base coat or resaturant on asphalt roll roofing.

TPO single-ply

Smooth white (sometimes gray or tan) plastic-feeling sheet with heat-welded seams that show a small lip; no granules. Repairs are best heat-welded. Never smear asphalt cement on it: contaminated TPO cannot be welded later and the section usually has to be cut out.

  • Silicone: Works with the right primer/prep. Scrub off the weathered surface; most systems call for a single-ply primer (especially on TPO under about five years old) and an adhesion test.
  • Acrylic (elastomeric): Works with the right primer/prep. Approved with a single-ply primer in systems such as JM’s; JM also wants the membrane at least a year old before coating.
  • Polyurethane (urethane): Possible, with caveats. Some urethane base coats list TPO, but adhesion to slick thermoplastic is the risk; pro system with primer only.
  • SEBS (synthetic rubber): Works with the right primer/prep. SEBS systems such as Mule-Hide’s list TPO, applied over the maker’s primer.
  • Fibered aluminum: Don't. Asphalt-based aluminum isn’t made for thermoplastic single-ply, and asphalt contamination stops future heat-welded repairs.
  • Asphalt emulsion: Don't. Asphalt on TPO contaminates the membrane so it can no longer be welded; GAF says such areas should be removed and replaced.

PVC single-ply

Looks very much like TPO — a smooth, usually white sheet with welded seams. Records or the installer are often the only sure way to tell them apart. Plasticizers in PVC react with asphalt products, so keep roof cement off it. Coating approvals vary more on PVC than on any other membrane.

  • Silicone: Possible, with caveats. Approvals split: Henry and GAF list PVC for silicone, while JM approves only acrylic on PVC; use a product that names PVC and run an adhesion test.
  • Acrylic (elastomeric): Works with the right primer/prep. Use only an acrylic whose data sheet lists PVC, over a single-ply primer; many retail acrylics, including Henry 587, exclude PVC.
  • Polyurethane (urethane): Possible, with caveats. Plasticizer migration and adhesion vary by membrane; only in a manufacturer-approved pro system.
  • SEBS (synthetic rubber): Possible, with caveats. The SEBS systems we checked list TPO and EPDM but not PVC; get written approval from the maker first.
  • Fibered aluminum: Don't. Henry excludes PVC sheet roofs, and asphalt and PVC plasticizers react with each other.
  • Asphalt emulsion: Don't. Asphalt products are not compatible with PVC; GAF warns plasticizer migration can soften both materials.

EPDM rubber

Matte black (occasionally white) rubber that feels like an inner tube, with taped or glued seams. Petroleum products make EPDM swell and soften: no asphalt cement, wet patch or aluminum coating. Patch with EPDM primer and tape.

  • Silicone: Works with the right primer/prep. The most common EPDM coating, but EPDM must be scrubbed with an EPDM cleaner and usually primed, then adhesion-tested.
  • Acrylic (elastomeric): Possible, with caveats. Many acrylics (Henry 587, JM’s system) exclude rubber; a few allow it over an EPDM-specific primer, so use one only if its data sheet lists EPDM.
  • Polyurethane (urethane): Possible, with caveats. Some urethane base coats list EPDM, but it is a pro system with specific cleaners and primers.
  • SEBS (synthetic rubber): Works with the right primer/prep. SEBS systems such as Mule-Hide’s list EPDM, applied over the maker’s primer.
  • Fibered aluminum: Don't. Henry excludes rubber roofs, and asphalt oils make EPDM swell and soften.
  • Asphalt emulsion: Don't. GAF warns asphalt oils migrate into EPDM and cause softening and swelling; Henry excludes rubber roofs.

Spray polyurethane foam

Seamless, textured surface with an orange-peel look, slightly springy underfoot; the foam is tan or yellow where the coating is worn. Foam must stay coated because sunlight degrades it. Recoat with an elastomeric coating (acrylic, silicone or urethane) before the foam is exposed.

  • Silicone: Good match. A standard foam topcoat; recoat before bare foam is exposed and fill any damaged foam first.
  • Acrylic (elastomeric): Good match. A long-standing foam system (GAF publishes an acrylic-over-SPF spec), but use an acrylic rated for SPF — Henry 587 excludes foam — and avoid areas that pond.
  • Polyurethane (urethane): Good match. Urethane coatings are a common choice on foam, especially where people walk; pro application.
  • SEBS (synthetic rubber): Possible, with caveats. Not a standard foam coating; get the maker’s written approval for SPF first.
  • Fibered aluminum: Don't. Henry excludes SPF roofs; foam needs an elastomeric coating.
  • Asphalt emulsion: Don't. Foam roofs are protected with elastomeric coatings (acrylic, silicone, urethane), not asphalt.

Low-slope metal

Standing-seam or ribbed metal panels at a low pitch, with exposed fasteners on ribbed panels. Rust and fasteners are the job: wire-brush rust, prime it, and seal or replace backed-out fasteners before coating.

  • Silicone: Works with the right primer/prep. Clean bare or rusty metal and use a rust-inhibitive primer, then seal seams and fastener heads before the field coat.
  • Acrylic (elastomeric): Works with the right primer/prep. Older uncoated or rusty metal needs a rust primer first (Henry and APOC both require it); seal fasteners and seams.
  • Polyurethane (urethane): Works with the right primer/prep. Good on metal over the maker’s epoxy primer; it is a pro system.
  • SEBS (synthetic rubber): Good match. Metal is the main SEBS market; some products are made for metal with light surface rust.
  • Fibered aluminum: Good match. Fibered aluminum is listed for weathered galvanized metal; new galvanized gets a light asphalt primer first.
  • Asphalt emulsion: Possible, with caveats. Some emulsions list metal roofs, but black asphalt makes metal hotter, so it is mainly used as a base under a reflective coat.

Already coated: silicone

A rubbery, slightly soft coating that water beads up on and that often looks grayish from dirt; tape and caulk barely stick to it. Only silicone sticks to silicone. Repairs and recoats must be silicone, after cleaning and an adhesion test.

  • Silicone: Good match. Silicone bonds to silicone without primer after a thorough wash; do an adhesion test, and repair with silicone sealant and fabric.
  • Acrylic (elastomeric): Don't. Acrylic will not bond to cured silicone.
  • Polyurethane (urethane): Don't. Urethanes will not bond to cured silicone.
  • SEBS (synthetic rubber): Don't. Not a recoat option over silicone.
  • Fibered aluminum: Don't. Henry specifically excludes silicone-coated roofs.
  • Asphalt emulsion: Don't. Asphalt products will not bond to cured silicone.

Already coated: acrylic

A harder, paint-like white film that leaves white chalk on your fingers when weathered. Can take acrylic or silicone after a wash and adhesion test. Peeling or blistered coating has to come off first.

  • Silicone: Good match. A common upgrade over sound acrylic: wash off chalk, remove loose coating and test adhesion. After this, only silicone can follow.
  • Acrylic (elastomeric): Good match. Like-over-like: wash, scrape any peeling coating, test adhesion and apply two coats.
  • Polyurethane (urethane): Possible, with caveats. Possible only if the urethane maker approves it over the existing acrylic and adhesion tests pass.
  • SEBS (synthetic rubber): Possible, with caveats. Solvent-based SEBS over old acrylic needs maker approval and an adhesion test.
  • Fibered aluminum: Don't. Not a listed surface for the fibered aluminum we checked, and it throws away the white coating you already have.
  • Asphalt emulsion: Don't. Not a listed surface for asphalt emulsions, and it turns a reflective roof black.

Calculator

Now: how much will you need?

Ranges use typical manufacturer spread rates plus 10% for waste and seams. Your product's data sheet always wins.

Typical for acrylic (elastomeric): 2–3 coats.

You'll need about

22–33 gal

  • 5–7 five-gallon pails
  • 5–7 4.75-gal buckets

Buy the high number for a first coat on a weathered roof; most stores take back unopened pails.

Coatings we'd look at

Check the label against your roof type before you buy. Typical price ranges, not live prices.

Silicone roof coating · $230–$330

HenryHenry 887 Tropi-Cool 100% Silicone White Roof Coating

Chemistry
Silicone
Size
4.75 gal
Coverage
About 320 sq ft per 4.75-gal pail at Henry's rate of 1.5 gal per 100 sq ft (22 dry mils minimum)
  • Mod bit
  • Built-up
  • Rolled
  • Metal
  • Spray foam
  • Silicone-coated
  • Acrylic-coated

The silicone most homeowners can actually find on a store shelf: bright white, tolerates standing water better than acrylic, and rain-safe minutes after it goes on. Buy enough to hit the full thickness, because a thin silicone coat is money wasted.

Read the fine print: Once a roof is silicone, only silicone sticks to it later. No acrylic, asphalt cement or most tapes over it. Henry calls for a test area on asphalt roofs to check bleed-through and adhesion, and it's not for shingles. An opened pail starts curing from the humidity in the air, so don't plan on saving leftovers.

Best for: Recoating a sound mod-bit, built-up, metal or foam roof with long-lasting white silicone

Check price on Amazon

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Silicone roof coating · $280–$400

GacoGacoRoof 100% Silicone Roof Coating, White (GR1600)

Chemistry
Silicone
Size
4.75 gal (sold as 5 gal)
Coverage
100 sq ft per gal per coat (about 11 dry mils on a smooth surface); Gaco calls for at least two coats, more on textured surfaces
  • Mod bit
  • Built-up
  • Rolled
  • Metal
  • Spray foam
  • Silicone-coated
  • Acrylic-coated

A silicone that contractors use and that is also sold retail. Plan on two full coats to reach the film build Gaco specifies; like other silicones it handles ponding areas better than acrylic.

Read the fine print: Gaco says to recoat GacoRoof only with more GacoRoof, and to run its adhesion test (or prime with its E5320 epoxy primer) on aged asphalt to head off bleed-through. Not for shingles. It's solvent-based, so expect odor and keep it away from open air intakes while you work.

Best for: Full-roof silicone restorations where you'll put down two proper coats

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Acrylic elastomeric roof coating · $90–$160

Kool SealKool Seal Premium Elastomeric White Roof Coating (10-year)

Chemistry
Acrylic
Size
4.75 gal (5-gal pail)
  • Mod bit
  • Built-up
  • Rolled
  • Metal
  • Spray foam
  • Acrylic-coated

A budget-friendly, water-based white coating for roofs that drain well. Cleanup is soap and water, and you can recoat it with acrylic again in a few years, which is why many homeowners start here.

Read the fine print: Acrylics need a dry, warm window to cure. Rain or heavy dew on a fresh coat can wash it off. Acrylic won't bond to silicone, and on asphalt surfaces brown staining can bleed through unless you prime.

Best for: A budget white recoat on a well-draining mod-bit, built-up or metal roof

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Aluminum roof coating · $110–$190

HenryHenry 555 Premium Fibered Aluminum Roof Coating

Chemistry
Aluminum
Size
4.75 gal
Coverage
Henry's rates: 2 gal per 100 sq ft on mineral cap sheet, 1.5 gal on smooth asphalt surfaces, 1.25 gal on metal
  • Mod bit
  • Built-up
  • Rolled
  • Metal

The classic silver coat for asphalt roofs: fibered asphalt loaded with aluminum flake that reflects sun and shields the membrane from UV. It costs less than white elastomerics and gets along with the asphalt underneath.

Read the fine print: Apply it only to a dry roof. Henry says no rain or dew within 24–48 hours, and a damp surface turns it brown. It's asphalt-based, so a future white acrylic or silicone recoat will need a thorough cleaning and usually a primer. Stir it well, because the aluminum settles.

Best for: Low-cost reflective protection on mod-bit, built-up and rolled roofs

Check price on Amazon

Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure

Coating questions

Can I put acrylic over a silicone-coated roof?

No. Acrylic, asphalt and aluminum coatings do not bond to cured silicone. Once a roof is silicone-coated, plan on silicone for every future recoat and repair.

Which coating is best for ponding water?

Most silicone data sheets rate it for ponding water (Henry 887 says "permanent ponding water resistant"), but many warranties still require the roof to drain within 48 hours.

Do I need a primer?

Often. Smooth or fresh asphalt (mod bit, built-up, roof cement) usually needs a bleed-blocking primer under a white coating, and single-ply membranes such as TPO and EPDM need the primer the coating maker specifies. The matcher flags these as "works with the right primer/prep".

Can I coat over a fresh asphalt patch like a wet patch?

Not right away. Asphalt patching products need to cure and weather first; data sheets range from about 30 days to a full summer, and a bleed-blocking primer is usually still required. Check both products’ data sheets.

Want the long version? Read what coating goes on my roof, silicone vs. acrylic and how to coat a flat roof. Rather not do it yourself? Get quotes from licensed roofers.