How to Repair an EPDM Roof: Cleaning, Priming, Patches and Cover Tape
Old rubber has to be scrubbed clean before any patch will stick. Find the leak, clean hard, prime, patch wide.
- Advanced
- 1 to 3 hours per repair
- Updated
The short answer
To repair EPDM, find the leak, scrub the area with a scrubbing pad and the manufacturer's cleaner until the rubber is clean and dull, apply primer, and cover the damage with a patch of cured EPDM or cover tape that extends at least 3 inches past it in every direction, with rounded corners. Roll it firmly. Do not use asphalt roof cement, which attacks rubber.
EPDM repairs are some of the simplest in roofing, provided the rubber is clean. The patch material is the same synthetic rubber as the roof, and self-adhering tapes and patches can cover a puncture or an open seam in an afternoon. What makes repairs fail is preparation. EPDM that has weathered for ten or twenty years has a chalky, oxidized surface that adhesives and tapes do not stick to until it is scrubbed.
The other problem is finding the leak. Water runs under adhered membrane and along the deck, so the stain is often far from the entry point. Check the usual places first: seams, T-joints, corners, pipe boots, edges and punctures from foot traffic, branches or tools. A patch on the wrong spot does nothing.
For how seams are made in the first place, see how to seam EPDM with seam tape. For leak tracing on any flat roof, see how to find a leak on a flat roof.
Tools
- Scrubbing pads or stiff brush
- Hand roller
- Scissors
- Utility knife
- Clean rags
- Primer brush or pad
- Hose for testing
Materials
- EPDM cover tape or cured EPDM patch with splice tape
- Primer and cleaner for weathered EPDM
- Uncured flashing for odd shapes
- Lap sealant for edges
- Termination bar and sealant for edge repairs
Safety first
- Wet EPDM is very slippery, and old EPDM can be chalky and slick. Wear clean, soft-soled footwear, and never repair on a wet or frosty roof.
- Cleaners and primers are flammable and fumes are harmful. Keep flames away and ventilate.
- A leak can mean rotten decking. Probe before you kneel, and step on framing lines. WorkSafeBC fall protection applies at 3 metres (about 10 feet) and wherever a fall of any height could cause serious injury.
Step by Step
Step 1: Find the leak and check the roof's condition
Start at the stain and work upslope. Inspect seams, T-joints, corners, pipe boots, edges and any punctures. A dry day is best, because open edges and gaps show. If the source is not obvious, water testing in sections from low to high isolates it.
Look at the overall roof. A few isolated defects on a supple roof are a repair job. Widespread cracking, brittle rubber, open seams across the roof and saturated insulation mean replacement is the honest answer.
Step 2: Clean the area thoroughly
Weathered EPDM has a layer of dirt, chalking and oxidation. Scrub it with a scrubbing pad and the recommended cleaner, wiping with clean rags in one direction, until the rubber is clean and the wipes come up free of black. Clean an area at least 2 inches wider than the patch on every side.
Do not use gasoline, mineral spirits or petroleum solvents on EPDM. They swell and damage the rubber.
Step 3: Dry the area and check the substrate
Water under the membrane must be dealt with. If a puncture has let water into insulation, the insulation may be wet and the patch will trap it. A small area can be dried, but widespread wetness calls for cutting out the wet insulation or replacing the section.
Patch only on a dry surface, above the tape and primer minimum temperature, commonly about 5 degrees Celsius.
Step 4: Prime the repair area
Apply a thin, even coat of primer with a clean pad over the area that the patch will cover, extending slightly past it. Prime the back of the patch too if the product calls for it. Let it dry to the touch, typically 5 to 20 minutes.
Do not touch the primed area. Dirt and oil stop the bond.
Step 5: Apply the patch or cover tape
For punctures and small tears, self-adhering cover tape or a cured EPDM patch with splice tape is used. Cut the patch with rounded corners, because square corners lift. It should extend at least 3 inches past the damage in every direction. Peel the film, press the patch down, and roll hard with a hand roller from the centre out.
Seal the edge with lap sealant if the manufacturer calls for it. For larger tears, a bigger patch or a replacement section is needed.
Watch out: Do not use asphalt roof cement or bituminous patching products on EPDM. Petroleum attacks the rubber and the repair fails.
Step 6: Repair open seams and lifted edges
For an open seam, fold back the top sheet, scrub and prime both faces, lay new splice tape, and roll it. If the old seam is too weathered, a cover strip of tape-backed EPDM over the seam is an option. See how to seam EPDM with seam tape.
For a lifted edge at a wall or drip edge, re-adhere the membrane, re-fasten the termination bar and reseal the top. See how to terminate EPDM at edges and walls.
Step 7: Address shrinkage at edges and penetrations
Over years, EPDM can shrink slightly, and a membrane that was installed with tension at a corner or an edge pulls away from the wall or curb. The fix is to release the membrane, re-adhere it with slack, and re-flash with a pre-formed corner or uncured flashing patch. See how to flash inside and outside corners on EPDM.
Shrinkage that keeps recurring is a sign the membrane is aging out.
Step 8: Test the repair and plan a follow-up inspection
Run water over the repair for several minutes and check inside. Photograph the work and mark it on a sketch of the roof. After the next heavy rain, go back and check the edges of the patch. Keep drains clear, because ponding stresses a repair faster than new work.
When Repair Stops Making Sense
- Brittle, cracked or crazed rubber across the field: the membrane is at the end of its life.
- Wet insulation: patching the top traps moisture and the roof will not dry.
- Seams opening across the roof: the tape or the sheet has failed overall.
- Repeated patches in the same place: the detail or the deck is the problem.
- Roof at 25 to 30 years old with many defects: replacement is usually the better value.
Fraser Valley Notes
Autumn is the best time for repair, before long wet weather sets in, and a dry spell in late winter is another window. Moss and needle debris hold water against patches and seams, so clean them off and keep drains clear. Tape and primer need a dry, mild day, so do not patch a roof in the rain just to stop a drip.
Common Mistakes
- Skipping the scrub. Weathered rubber is chalky and the patch peels within a season.
- Asphalt roof cement. It attacks EPDM and the patch fails.
- Patches under 3 inches of lap. The patch lifts at the edge.
- Square patch corners. They lift first and let water in.
- Patching over wet insulation. The roof never dries and the damage spreads.
- Ignoring the cause. A patch on a ponding roof or at a moving pipe fails again.
When to Call a Professional
If the leak cannot be found, if insulation is wet, if seams are opening along many feet or if the roof is old and brittle, call a roofer. They can judge whether repair makes sense and, where it does not, plan replacement.
If you are replacing an EPDM roof, see how to install a fully adhered EPDM roof for what the new roof involves.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Flat Roofing and Torch On service or the towns we cover.
How to Repair an EPDM Roof: Questions
Can you patch an EPDM roof yourself?
Small punctures and tears can often be patched with EPDM cover tape or a cured EPDM patch, provided the old rubber is scrubbed clean, primed and dry and the patch extends at least 3 inches past the damage. Finding the real leak source, dealing with wet insulation and repairing seams and flashings are harder, and are best left to a roofer.
Why will tape not stick to old EPDM?
Old EPDM develops a chalky, oxidized surface and collects dirt, which blocks adhesive. It must be scrubbed with a scrubbing pad and the manufacturer's cleaner until the rubber looks clean and dull, then primed. Even then, very old or brittle rubber may not hold a patch, which is a sign the roof is near the end of its life.
Can you use roof cement on EPDM?
No. Asphalt based roof cement and tar products contain petroleum that attacks EPDM rubber, softening it and causing repairs to fail. Use EPDM cover tape, splice tape with primer, or a cured EPDM patch, and sealants approved by the membrane manufacturer. Asphalt repairs already on a roof should be cleaned off before patching.
Why is my EPDM pulling away at the edges?
EPDM can shrink slightly over time, and a membrane installed with tension at edges, corners or pipes pulls away as it shrinks. Loose terminations and failed adhesive add to it. The repair is to release the tension, re-adhere the membrane with slack, re-fasten the termination bar and re-flash the corner. Repeated shrinkage means the membrane is aging.
Related Guides
All EPDM Rubber Roofing guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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