How to Seal Corrugated Metal Roof Seams: Complete 11-Step Professional Guide (2025)

Step 1: Safety First - Set Up Fall Protection

Why this matters: Falls from roofs are the #1 cause of construction deaths. Corrugated metal is especially slippery when wet or dewy.

• • Install roof anchors or use chimney anchor strap system
• • Wear full-body harness connected to lifeline
• • Use ladder standoff to prevent gutter damage
• • Work with a partner (someone on ground level)
• • Check weather: NO work if rain, high winds (15+ mph), or ice predicted

Step 2: Inspect All Seams and Identify Problem Areas

Walk the entire roof and document every seam that needs attention. Look for:

• • Cracked or missing sealant: Indicates UV degradation or failed application
• • Rust stains or corrosion: Water has been penetrating (needs rust treatment)
• • Lifted or separated panels: Wind damage or thermal movement
• • Gaps wider than 1/4": Require backer rod before sealing
• • Standing water pools: Drainage issue (needs addressing before sealing)

Pro tip: Take photos with your phone and mark problem areas with chalk or removable tape for reference.

Step 3: Remove Old, Failed Sealant Completely

New sealant won't bond properly over old, degraded material. This is the most time-consuming step but critical for success.

• • Use a putty knife or 5-in-1 tool to scrape away old caulk
• • For stubborn sealant, apply mineral spirits and let sit 10-15 minutes
• • Use wire brush to remove residue from metal surface
• • For large areas, use drill with wire cup brush attachment (faster)
• • Clean out seams completely—any residue prevents new sealant adhesion

Step 4: Address Rust and Corrosion (Critical for Coastal Roofs)

Myrtle Beach's salt air accelerates rust at seam fasteners and edges. Sealing over rust guarantees failure.

• • Light surface rust: Remove with wire brush, then apply rust converter primer
• • Moderate rust: Use angle grinder with wire wheel to remove, then prime
• • Severe rust (holes or deep pitting): Panel replacement required (not DIY-able with sealant)
• • Apply rust-inhibiting metal primer to bare areas (let dry per manufacturer specs)
• • For fastener rust: Consider replacing rusted screws with stainless steel or coated fasteners

Product recommendation: Rust-Oleum Rust Reformer converts rust to stable surface (apply before sealant).

Step 5: Clean and Degrease All Seam Surfaces

Sealant requires a clean, dry surface for proper adhesion. Coastal roofs accumulate salt residue, algae, and industrial pollutants.

• • Mix TSP (trisodium phosphate) or metal roof cleaner per label directions
• • Scrub seam areas with stiff brush and cleaner solution
• • For grease/oil contamination: Use degreaser (Simple Green, Purple Power)
• • Rinse thoroughly with clean water (garden hose)
• • Let dry completely—at least 24 hours in humid Myrtle Beach climate

Step 6: Apply Metal Roof Primer (Highly Recommended)

While not always required, primer significantly improves sealant adhesion and longevity—especially on painted or coated metal.

• • Choose primer compatible with your sealant (check manufacturer specs)
• • Apply thin, even coat along seam areas using brush or foam applicator
• • Let dry per label (typically 30 minutes to 2 hours)
• • Don't skip this on Kynar/PVDF-coated metal—primer is essential

Recommended: Titebond Metal Roof Primer or Geocel Pro-Prime (both tested for coastal applications).

Step 7: Install Backer Rod for Wide Gaps (If Needed)

Gaps wider than 1/4" require backer rod to prevent sealant from sagging and to improve adhesion.

• • Measure gap width and select backer rod 1/8" larger than gap
• • Push backer rod into seam using putty knife or blunt tool
• • Rod should sit 1/4" to 1/2" below surface (not flush)
• • Creates proper sealant depth and prevents "three-sided adhesion" (causes failure)

Step 8: Apply Sealant Using Proper Technique

This is the critical step where most DIY failures occur. Follow these professional techniques:

Application Method

• • Temperature window: Apply when surface temp is 55°F-90°F (check with IR thermometer)
• • Cut nozzle angle: 45-degree angle, opening sized to match seam width
• • Bead size: 1/4" to 3/8" bead for most corrugated seams
• • Application speed: Steady, consistent pressure and movement (not too fast or slow)
• • Overlap: If stopping mid-seam, create 1" overlap when resuming

Sealing Pattern for Corrugated Roofs

1. Horizontal seams (panel overlaps): Apply continuous bead along top and bottom edges of overlap
2. Vertical seams (end laps): Seal both sides where panels meet
3. Fastener heads: Apply small dab over each exposed fastener
4. Ridge caps: Seal where ridge cap meets panels on both sides
5. Flashing transitions: Seal where metal meets flashing at walls, chimneys, vents

Step 9: Tool and Smooth Sealant Immediately

Tooling creates proper seam adhesion and prevents water from wicking under sealant edges.

• • Within 5-10 minutes of application (before skinning over)
• • Use plastic spoon, popsicle stick, or professional sealant tool
• • Smooth sealant into seam with firm, consistent pressure
• • Ensure sealant contacts both sides of seam (critical for waterproofing)
• • Remove excess sealant with rag dampened in mineral spirits
• • Create slight concave profile (edges higher than center)—sheds water better

Don't use your finger to smooth—body oils can contaminate sealant and reduce adhesion.

Step 10: Inspect and Touch Up Any Gaps

Walk the entire roof once more and check your work carefully.

• • Look for voids, air bubbles, or thin spots in sealant
• • Check that all seams have continuous bead coverage
• • Verify sealant adheres to both sides of every seam
• • Touch up any missed fasteners or transition points
• • Look from ground level—sometimes gaps are more visible from different angles

Step 11: Allow Proper Cure Time Before Rain Exposure

This is where many coastal projects fail—unexpected afternoon thunderstorms during cure.

• • Minimum cure time: 24-48 hours before rain (check product label)
• • Full cure time: 7-14 days for maximum strength
• • Temperature matters: Cure time increases in cold weather, humidity slows cure
• • Check 48-hour weather forecast before starting project
• • If rain is forecast within 48 hours, delay project or use fast-cure sealant