Video · Coatings
A DIY Silicone Coat Over Modified Bitumen
- Mod bit
What this video shows
A do-it-yourselfer coats a modified bitumen roof with Henry's 100% silicone. It's a real-world look at one of the most common Florida flat-roof restorations, white silicone over an aging mod-bit cap sheet, from a homeowner's point of view instead of a manufacturer's.
Key points
- Mod bit is a good candidate for silicone if the membrane is still well attached and dry underneath. Coating won't fix wet insulation or blisters.
- Granulated surfaces soak up more coating than smooth ones, so budget extra material beyond the textbook coverage rate.
- Clean thoroughly and let it dry. Silicone bonds poorly to dust, loose granules and chalky residue.
- Test a small area first. Brown staining in the white means asphalt is bleeding through and you need a bleed-blocking primer.
- Decide before you start: after silicone, every future repair and recoat has to be silicone too.
Products in this video
The products used or shown, or the closest match we could verify. 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 for Henry 887 Tropi-Cool 100% Silicone White Roof Coating (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Roof cleaner / coating prep · $25–$50
Rust-OleumRust-Oleum One-Step Roof Prep Cleaner, 1 gal
- Size
- 1 gal
- Mod bit
- Built-up
- Rolled
- Metal
- Spray foam
- TPO
- EPDM
- Acrylic-coated
- Silicone-coated
A roof-specific cleaner for getting dirt, chalk and mildew off before a coating goes on. Most coating failures trace back to prep, and this is the cheap part of the job.
Read the fine print: Rinse completely and let the roof dry, because cleaner residue blocks adhesion. Follow the label for dilution and protecting plants, and check that your coating maker accepts it as prep.
Best for: Washing a roof before priming or coating
Check price on Amazon for Rust-Oleum One-Step Roof Prep Cleaner, 1 gal (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Asphalt bleed-blocking primer · $100–$300 (depends on pail size)
Tropical Roofing Products (TRP)TRP #996 Eterna-SIL Premium Bleed Blocker
- Mod bit
- Built-up
- Rolled
A primer that seals asphalt surfaces so brown oils don't stain up through a white silicone topcoat. TRP is a Florida coatings maker, and this is a step pros don't skip on older mod-bit and asphalt-patched roofs.
Read the fine print: Use it with the silicone system it's designed for, and wait the maker's dry time before topcoating. Fresh asphalt cement and wet-patch repairs still need to cure before you prime over them.
Best for: Priming mod-bit, built-up or asphalt-patched roofs before silicone
Check price on Amazon for TRP #996 Eterna-SIL Premium Bleed Blocker (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Roller cover (3/4 in. nap) · $6–$12
WoosterWooster Pro/Doo-Z 3/4 in. Nap Roller Cover, 9 in. (RR644-9)
- Size
- 9 in.
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
A shed-resistant 3/4-inch nap holds enough thick roof coating to work it into granules and rough surfaces. Buy several, because silicone ruins roller covers and you won't be cleaning them.
Read the fine print: For heavy silicone, some pros step up to a 1-inch nap. Either way, swap the cover when it mats down instead of trying to stretch it.
Best for: Rolling acrylic or silicone coatings and primers
Check price on Amazon for Wooster Pro/Doo-Z 3/4 in. Nap Roller Cover, 9 in. (RR644-9) (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Wet mil gauge · $7–$15
GenericWet Film Thickness Gauge, hex comb (1–118 mil)
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
A cheap stainless comb you press into fresh coating to read wet mils. It's how you know you're putting down what the data sheet calls for instead of guessing, and how a homeowner can check a contractor's work.
Read the fine print: Wet mils aren't dry mils. Use the coating's spec sheet to convert, since water-based acrylics shrink more than silicones as they cure. Wipe the gauge clean after every reading.
Best for: Checking coating thickness as you roll
Check price on Amazon for Wet Film Thickness Gauge, hex comb (1–118 mil) (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Read the full guide
Coatings What coating can go on my flat roof? Start with what's on the roof now. Asphalt roofs (modified bitumen, built-up and roll roofing) take most coatings but need a bleed-blocking primer under white silicone. EPDM rubber takes silicone after an EPDM cleaner and primer but never asphalt products, and TPO and PVC need a single-ply primer and a coating whose label names them. Spray foam takes acrylic, silicone or urethane, and a silicone-coated roof accepts only more silicone.Video by Handywoman, embedded from YouTube. The summary, key points and cautions on this page are our own; Handywoman doesn't endorse TheFlatRoofPro.com or the products listed. Roofing work for hire generally requires a licensed roofing contractor.