8.5 Roof Repair Techniques by System

8.5 Roof Repair Techniques by System

Section 8.3 answers where is the leak and what does the code allow. This section answers how do you actually fix it. The CR-42 blueprint devotes four questions to Repairs and Reroofing, and repair questions are almost always system-specific: the correct patch for an EPDM seam is wrong for TPO, and the correct blister repair for BUR has no analog in tile. Repair is also the highest-volume work in the Arizona market, because a desert roof usually fails at details long before the field membrane is spent.

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1. Triage: Temporary, Interim and Permanent

The universal precondition applies to every permanent repair: the substrate must be dry. Patching over trapped moisture guarantees a blister, and it is the workmanship defect the ROC most reliably confirms on inspection.

[!WARNING] Never use asphalt roof cement as a permanent repair on a single-ply membrane. Asphaltic products attack EPDM, and they are incompatible with TPO and PVC welds. A black mastic smear on a white membrane is the visual signature of a repair that will fail and will void the warranty.

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2. Built-Up Roofing

Blisters. A blister is a pocket of entrapped air or moisture between plies or between the membrane and substrate. Sound, unbroken blisters that are not in a traffic path are frequently left alone and monitored — cutting them creates a repair where none was needed. Broken or leaking blisters are repaired by:

1. Cutting an X through the blister to the sound substrate, not through it
2. Folding back the flaps, removing all wet felts and dried mastic, and letting the area dry
3. Priming with ASTM D41 primer where bare substrate is exposed
4. Setting the flaps back into hot asphalt or cold adhesive
5. Installing a two-ply patch with staggered dimensions — the first ply extending at least 6 inches beyond the cut in all directions, the second at least 12 inches — with rounded corners on both
6. Surfacing to match, re-embedding gravel where applicable

Splits and ridges. Splits usually track over an insulation joint or a deck joint and indicate a movement problem, not a membrane problem. Repair the split with the same two-ply staggered patch, but first ask why it split: a recurring split over the same joint calls for an area divider or a properly detailed expansion joint per Section 7.4.

Fishmouths, alligatoring and slippage. Fishmouths at ply laps are cut, mopped and patched. Alligatoring of a smooth-surfaced BUR indicates the flood coat has oxidized and is a candidate for the restoration coatings in Section 5.5. Felt slippage on slopes signals an asphalt with too low a softening point for Arizona — the ASTM D312 selection discussion in Section 5.1.

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3. Modified Bitumen

Patch with the same membrane type and the same application method as the original: torch-applied APP is patched with torch-applied APP, self-adhered SBS with self-adhered SBS. Requirements that show up on exams:

• Round the corners of every patch — square corners concentrate stress and peel
• Extend the patch a minimum of 6 inches beyond the damage in all directions
• Prime the existing surface where granules or oxidation would prevent bond, or scrape granules back and use a granule-embedding compound
• Verify bleed-out at the patch perimeter on torched and mopped work — a visible bead of bitumen proves the lap is sealed
• Where a patch crosses an existing lap, treat the resulting T-joint with the 45-degree corner cut described in Section 5.2
• Torch work triggers the full CERTA protocol and the two-hour fire watch from Section 8.2

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4. Single-Ply Membranes

Single-ply repair depends entirely on identifying the polymer first. Getting this wrong destroys the roof.

EPDM (thermoset)

1. Clean the area with the manufacturer's splice cleaner, not solvent of convenience
2. Apply seam primer and let it flash off to the specified tack
3. Apply seam tape and roll it firmly, or use a self-adhered cover strip
4. The patch must extend at least 3 inches beyond the damage in every direction, with rounded corners
5. Apply lap sealant to all cut edges of the patch
6. Use uncured (non-reinforced) EPDM flashing for irregular shapes such as pipe bases and corners, because it stretches into contours that cured sheet cannot

TPO and PVC (thermoplastic)

1. Clean per the manufacturer; for PVC and weathered TPO, use the specified cleaner to remove the weathered surface layer
2. Hot-air weld the patch, by robotic welder for long runs or hand welder with a silicone roller for detail
3. Manufacturers commonly require a minimum 1½-inch continuous weld width
4. Round every corner of the patch and extend it well past the damage
5. Probe the entire weld with a blunt, rounded tool to find skips and cold welds
6. Pull daily test coupons — 1-inch-wide strips cut across the weld — and confirm a film-tearing bond, in which the membrane tears before the weld separates
7. Adjust the welder for ambient temperature, wind and membrane age; a setting that welded correctly at 6:00 a.m. will scorch at 2:00 p.m. on an Arizona roof

Compatibility Rules

• TPO cannot be welded to PVC. They are both thermoplastic but chemically incompatible.
• PVC plasticizers migrate. Never patch PVC with EPDM, asphaltic products or non-PVC-compatible sealants.
• EPDM cannot be heat welded at all; it is a thermoset and must be adhered.

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5. Spray Polyurethane Foam and Coated Roofs

1. Probe the perimeter of the damage to find the extent of wet foam — a moisture meter or a simple screwdriver probe reveals soft, saturated foam
2. Cut out all wet foam back to dry, sound material and to the substrate where necessary
3. Bevel the cut edges so the new foam feathers into the existing surface with no ledge to collect water
4. Re-spray to match the existing thickness, keeping the profile smooth
5. Recoat the repair and a generous overlap area to the specified dry mils using the same chemistry already on the roof — remembering the rule from Section 5.5 that only silicone bonds to silicone
6. Broadcast granules into the wet coating at walkways and service areas

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6. Tile

Arizona's dominant steep-slope system, and the one with the most misunderstood repair logic. The tile is the shedding surface; the underlayment is the waterproofing. A leak under an intact tile field is almost always an underlayment or flashing failure, and replacing tiles will not fix it.

To replace a broken tile:

1. Work from the ridge down so overlying tiles can be lifted without breaking them
2. Lift the tile in the course above and the tiles on either side, propping them with wedges
3. Remove or cut the fastener holding the broken tile — a slater's ripper or a hacksaw blade reaches nails under the course above
4. Slide the broken pieces out, inspect the underlayment beneath, and repair the underlayment before proceeding
5. Slide the replacement in and fasten it, or where the head cannot be nailed, secure it with a nose clip, storm clip or copper wire tie
6. Confirm the headlap and side lap match the surrounding field

Because concrete tile colors change over time and profiles are discontinued, salvage tiles from an inconspicuous area — a rear slope or under a future solar array — and place the new, unweathered tiles there.

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7. Asphalt Shingles

1. Work in cool morning temperatures. Warm shingles tear; cold shingles crack. Mid-morning is the compromise.
2. Break the factory sealant bond with a flat bar, working from the course above downward
3. Remove eight nails: the four fastening the damaged shingle, plus the four in the course above that penetrate its top edge
4. Slide the damaged shingle out and the replacement in, aligning the exposure and the butt line
5. Renail in the correct nailing zone, then renail the course above
6. Hand-seal with a quarter-sized dab of ASTM D4586 asphalt roof cement under each tab. Excess cement is a defect, not extra insurance — a heavy bead prevents the shingle from lying flat and causes blistering and buckling.

Match the shingle by product line and color lot where possible; weathering means a perfect match is rarely achievable, which is a conversation to have with the owner before the repair, not after.

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8. Metal Roofing

• Backed-out fasteners are the number-one metal repair. Replace with oversize-diameter screws and new EPDM-bonded washers — never simply retighten a stripped hole, and never add sealant over a loose screw.
• Panel seams and end laps are repaired with butyl tape inside the lap and mechanical fastening, not with a surface bead of caulk.
• Patches must be the same alloy and coating as the panel. A steel patch on an aluminum roof, or a copper patch on galvanized, creates the galvanic cell described in Section 4.3 and will corrode a hole through the panel.
• Rust is treated back to sound metal, primed with a compatible rust-inhibitive primer, and stripe-coated; heavily perforated panels are replaced, not patched.
• Sealant-only repairs fail. Every sealed joint should also be mechanically locked or riveted, as covered in Section 7.4.

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9. Flashings, Pitch Pans and Documentation

Pitch pans (sealant pans) are the highest-maintenance detail on any roof and the most common source of repeat leaks. Refill by removing the failed sealant to the bottom of the pan, cleaning the penetration and pan walls, filling with a two-part pourable sealer, and crowning the finished surface so water sheds off rather than pooling. Where the design permits, replace the pitch pan with a welded or fabricated flashing instead.

Documentation and warranty. Before touching a roof under a manufacturer's no-dollar-limit warranty, verify who is authorized to repair it. NDL and system warranties almost always require a manufacturer-certified contractor and prior notification; an unauthorized repair — even a technically correct one — can void coverage on the entire roof. Photograph the defect, the prepared substrate and the completed repair; record materials, lot numbers and weld or bleed-out verification. That record is the contractor's defense during the two-year ROC complaint window under A.R.S. § 32-1162.

Repair Selection Quick Reference