How to Coat a Rusted Metal Roof with Silicone
If you’ve got a rusted metal roof, you already know the deal—left untreated, rust eats away at the metal, weakening it until you’re dealing with leaks, mold, and expensive damage. The good news? You can extend the life of that roof without a full tear-off. With the right prep and a few solid products, you can coat a rusted roof with silicone and make it watertight again.
Here’s a step-by-step guide to help you get it done.
Step 1: Don’t Skip Safety
This part isn’t optional. Wear non-slip shoes. Use a stable ladder. If you’re on a tall roof, use a harness. Don’t do this alone, and don’t do it if the roof is wet.
Step 2: Inspect the Roof and Clean It Up
Start by walking the roof and checking for:
· Heavy rust
· Loose or missing fasteners
· Holes or cracked seams
Use a wire brush or scraper to remove flaking rust and paint. You don’t need a perfect bare metal surface—but you do need a clean one. Tighten or replace any loose screws while you're up there.
Then clean the whole roof. Power washing is ideal—it gets rid of dirt, oil, mold, and debris. Let it dry completely before moving forward.
Step 3: Prime the Rust
Once the roof’s clean, hit the rusted areas with Rust Buster, a rust-inhibitive primer. This step slows down future corrosion and helps your silicone stick better. Follow the label for drying times.
Step 4: Seal All Seams and Fasteners
Use Heavy-Duty Silicone or Seam Slayer to cover every seam, fastener, and transition point. These spots are the first to leak, so take your time here. Give it 24 hours to cure before applying your top coat.
Note: If you skip prep or rush this step, your coating won’t last. Don’t cut corners.
Step 5: Apply the Silicone Top Coat
Now for the fun part. Stir your Silicone Top Coat thoroughly and apply it with a roller or brush. Work in sections, starting at the far end of the roof and moving toward your ladder. Follow the manufacturer’s specs for thickness—check our coverage guide here.
If the roof is in rough shape, consider a second coat for extra protection.
Step 6: Let It Cure
The coating will usually dry to the touch in a few hours, but full cure takes 24–48 hours depending on the weather. Keep off the roof during this time.
Final Thoughts
Rust doesn’t fix itself—and if you ignore it, you’re setting yourself up for major repairs down the road. A silicone coating system is a smart, affordable fix. It adds years of life, seals leaks, and keeps UV and water out. If you're handy and follow the steps, this is a project most homeowners or contractors can knock out without a problem.
Got questions? Reach out to your local CMC rep here.