Roofing discussions and local services.
Is This Salt Residue or Corrosion in My Roof Flashing?
Discussion options
I’m trying to determine whether the white crust and dark pitting on coastal roof flashing are mostly surface salt deposits or signs that the metal is failing.
The flashing is approximately 8 years old, but I’m not sure whether it’s aluminum, galvanized steel, or another alloy. The affected areas are around the chimney and a wall-to-roof junction on the ocean-facing side. There’s also some discoloration below one joint, although I haven’t found damp sheathing or interior staining. The roof was exposed to a strong recent storm, and a nearby section has stainless fasteners while the flashing may be galvanized.
- Does white crust usually clean off as salt residue, or can it accompany galvanic corrosion?
- How much pitting or joint movement is enough to justify replacing the flashing rather than cleaning and monitoring it?
- Could the staining below the joint indicate an active leak even if the attic is currently dry?
- What’s the safest way to identify the flashing metal and inspect the joint without damaging the roof covering?
I’m mainly trying to separate a maintenance issue from a repair that needs a roofer or more detailed inspection.
2 replies
A dry attic doesn’t rule out an active or intermittent leak. Water from that wall-to-roof joint can run along the flashing or framing, then evaporate or exit elsewhere before it produces interior staining. Since there’s already discoloration below the joint, I wouldn’t assume the white material is only salt residue.
After a dry period, a roofer can perform a controlled hose test, starting below the joint and working upward while someone checks the underside. Avoid spraying upward under the flashing or using a pressure washer. The test should be stopped if water appears, and the joint should be inspected for open seams, lifted edges, failed sealant, and pitting through the metal. Surface crust that wipes off after gentle rinsing is less concerning, but pitting, movement, or a seam that admits water points toward repair or replacement rather than monitoring alone.
The hose test may help locate an active leak, but it won’t answer the metal-condition question.
- White crust can be salt, corrosion product, or both. Galvanic contact between stainless fasteners and galvanized flashing can accelerate zinc loss, especially in a coastal environment.
- Don’t scrape aggressively or probe with a screwdriver. That can puncture already-thinned metal and make the test misleading.
- A roofer can identify the material from an inconspicuous exposed edge, fastener relationship, or coating pattern. They should also check whether pitting has reduced the metal enough to flex, perforate, or pull away at the joint.
- If the discoloration below the joint remains after drying, treat it as a reason for closer inspection even if the attic is currently dry. A hose test can find water entry, but it can’t establish that the flashing is structurally sound.
Join the conversation
Share your experience or ask a follow-up question.