Video · Leaks & repairs
How a Manufacturer Repairs Modified Bitumen
Watch “SOPREMA Modified Bitumen Membrane Repair Procedure” on YouTube (opens in new tab)
- Mod bit
What this video shows
SOPREMA, a major modified bitumen manufacturer, walks through its repair procedure for damaged mod-bit membrane. It's the professional benchmark to compare quick fixes against, useful for DIYers deciding what they can handle and for pros matching manufacturer requirements.
Key points
- Proper mod-bit repairs remove or open the damaged area, dry it, and add new membrane that overlaps sound material.
- Where new material bonds, the granules have to be removed or embedded first.
- Torch-applied repairs are pro-only work. Open flame on a roof is a leading cause of roofing fires.
- Roof cement plus fabric is a valid temporary or small-area fix, but it won't last as long as a membrane patch.
- Find out what's under the damage. Wet insulation means a bigger repair than a surface patch.
Products in this video
The products used or shown, or the closest match we could verify. Typical price ranges, not live prices.
Wet-or-dry roof cement · $20–$40
HenryHenry 208R Rubberized Wet Patch Roof Cement (HE208R042)
- Chemistry
- Asphalt
- Size
- 0.90 gal (1-gal can)
- Coverage
- About 12.5 sq ft per gallon at 1/8 in. thick
- Mod bit
- Built-up
- Rolled
- Metal
The emergency patch to keep in the garage: a rubberized asphalt cement that bonds to wet surfaces, even in the rain. Trowel it on thick and wide, and bed polyester fabric in it over anything bigger than a nail hole.
Read the fine print: Asphalt-based. Henry says to wait 30 days before coating over it, and it can bleed through white acrylic or silicone, so prime it with a bleed blocker or cut it out before a recoat. Not for EPDM rubber or PVC sheet roofs. Henry wants fabric on any hole wider than 1/4 in. or longer than 2 in.
Best for: Stopping an active leak on a mod-bit, built-up, rolled or metal roof
Check price on Amazon for Henry 208R Rubberized Wet Patch Roof Cement (HE208R042) (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
Plastic roof / flashing cement · $20–$40
GardnerGardner Wet-R-Dri All Weather Plastic Roof Cement
- Chemistry
- Asphalt
- Size
- 1 gal
- Mod bit
- Built-up
- Rolled
- Metal
An all-weather asphalt plastic cement for setting flashing, sealing laps and filling cracks on asphalt roofs. A solid alternative when the Henry is out of stock.
Read the fine print: Like every asphalt cement, it stays soft for weeks and stains white coatings. Don't topcoat it with acrylic or silicone until it has cured and been primed with a bleed blocker.
Best for: Flashing, laps and cracks on mod-bit, built-up and rolled roofs
Check price on Amazon for Gardner Wet-R-Dri All Weather Plastic Roof Cement (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
Polyester reinforcing fabric · $15–$35
HenryHenry 296 Polyester Repair Fabric, 4 in. x 150 ft
- Chemistry
- Other
- Size
- 4 in. x 150 ft
- Mod bit
- Built-up
- Rolled
- Metal
- Spray foam
- Acrylic-coated
- Silicone-coated
Thin, stretchy polyester you bed into roof cement or coating to bridge cracks, seams and flashing joints. It's the difference between a patch that splits in a month and one that lasts.
Read the fine print: Fabric goes into a wet base layer and must be fully covered by a top layer. Exposed fabric wicks water and breaks down in the sun.
Best for: Reinforcing patches, seams and flashing transitions
Check price on Amazon for Henry 296 Polyester Repair Fabric, 4 in. x 150 ft (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
Utility knife · $12–$22
StanleyStanley 10-777 FatMax Locking Retractable Utility Knife
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
Cuts fabric, membrane, cover tape and failed sealant. A locking blade matters when you're pushing through tough roofing material.
Read the fine print: Add a pack of hook blades for cutting membrane from the top without slicing what's underneath, and change blades often.
Best for: Cutting fabric, membrane patches and old sealant
Check price on Amazon for Stanley 10-777 FatMax Locking Retractable Utility Knife (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
Margin trowel · $10–$20
MarshalltownMarshalltown Margin Trowel, 5 x 2 in.
- Mod bit
- Built-up
- Rolled
- Metal
Small enough to scoop roof cement out of the can and work it into tight spots around flashing, and stiff enough to spread it 1/8 inch thick.
Read the fine print: Asphalt cement doesn't wash off with water. Keep mineral spirits and rags on hand for cleanup.
Best for: Applying roof cement and wet patch
Check price on Amazon for Marshalltown Margin Trowel, 5 x 2 in. (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
Leaks & repairs How to patch a flat roof leak On an asphalt-based flat roof (modified bitumen, built-up or roll roofing), a rubberized wet-patch cement such as Henry 208R can be troweled on even in the rain to stop a leak today. The lasting repair is a fabric-reinforced three-course patch, or on EPDM, TPO and PVC a patch of matching membrane, because asphalt cement damages rubber and PVC and ruins TPO for future welding. If you plan to coat later, Henry says to wait 30 days over its wet patch, and white coatings may need a bleed-blocking primer.Video by SOPREMA USA, embedded from YouTube. The summary, key points and cautions on this page are our own; SOPREMA USA doesn't endorse TheFlatRoofPro.com or the products listed. Roofing work for hire generally requires a licensed roofing contractor.