Knowing how to waterproof metal roofing is a handy skill for any DIYer. More and more homeowners are skipping the contractor and waterproofing their metal roofs themselves with liquid rubber coatings. They're easy to use, affordable and reliable.
This guide covers the basics of waterproofing a metal roof: why it matters, what causes leaks, which DIY metal roof coating to use and how the job comes together.
Why Waterproofing a Metal Roof Matters
Metal roofs are known for their durability and long life, which makes them a worthwhile investment. But they still need protection from the elements. Over time, harsh weather wears down fasteners, causes rust and can compromise the structure of your roof.
Metal roof waterproofing means applying a protective coating over the surface of your roof. It goes on as a liquid and dries into a flexible, waterproof membrane. Here's what it does for you:
- Fights rust and keeps water out, the two biggest threats to a metal roof
- Helps protect against wind damage, which can lead to lost fasteners or loose panels
- Extends the life of your roof by preventing corrosion
- Refreshes the look of a roof that's starting to show its age
- Helps cut down on noise from rain and hail
What Causes Leaks in Metal Roofs?
Before you start waterproofing, find out where water is getting in. Common signs of a leaking metal roof include:
- Loose or missing fasteners
- Damaged panels
- Open headwalls or flashing
- Missing trim
- Gaps in seams
- Rust damage
Leave these alone and they can lead to serious water damage to your roof and the structure underneath it.
Choosing a DIY Metal Roof Coating
The right DIY metal roof coating depends on what your roof needs. Liquid Rubber makes two for metal roofs. Both go on with a brush, roller or sprayer. Once dry, they repel water and have very low water vapor transmission, so they fully seal the surface and keep moisture out.
MetalSafe Sealant
If rust is your main concern, go with MetalSafe Sealant. It's a bitumen-based sealant with built-in rust inhibitors, and it goes right over light surface rust with no primer needed. It bonds to galvanized steel, aluminum and copper, resists a wide range of chemicals and temperatures, and helps protect against hail, chipping and abrasion. The catch? It only comes in black.
Color Roof Sealant
Want color? Color Roof Sealant comes in nine color options, including clear. If your roof has any rust, prime those spots with a water-based rust primer or converter first.
Tin Roof Waterproofing
Got an older tin roof or a corrugated tin shed? MetalSafe Sealant works on those too. Most older "tin roofs" are actually corrugated galvanized steel or iron coated in a layer of tin, and MetalSafe is compatible with both. That makes it a solid pick for sealing old panels and stopping leaks.
A couple of things to watch for:
- Rust: If the tin has light, tight rust, you can paint MetalSafe right over it. Wire-brush away any loose, flaking rust or scale first.
- Seams and fasteners: Older tin roofs tend to shift, which causes leaks around the original nails, screws and overlapping seams. Bridge those joints with Seam Tape before you coat.
How to Waterproof a Metal Roof: The Quick Version
Whether you're working out how to waterproof steel, aluminum or tin roofing, the process is the same. Here's the overview:
- Inspect and repair. Tighten, add or replace loose fasteners and fix any damage you find.
- Clean the roof. Remove loose debris and rust, use Multipurpose Cleaner on tougher grime, then pressure wash.
- Let it dry completely. If the roof is still wet, the coating won't stick properly.
- Fill small cracks. Use Sealant & Adhesive Caulk on cracks and joints between 1/8 and 1/2 inch.
- Treat rust spots. Prime them if you're using Color Roof Sealant. MetalSafe doesn't need a primer over light rust.
- Bridge the seams. Apply Seam Tape over seams, joints, vents and flashing.
- Apply your coating. Use a brush, roller or sprayer, and let each coat dry before the next one.
For the full walkthrough, including dry times, coverage and how many coats to apply, check out our step-by-step guide: How to Seal a Metal Roof.
The Best Time to Waterproof Your Metal Roof
The best time to waterproof your metal roof is when temperatures stay between 50°F and 86°F (10°C and 30°C), out of direct sun, with no rain in the forecast for 24 hours. If you get morning dew, start early in the day. That gives each coat time to dry before the next morning.
Common Mistakes to Avoid
Waterproofing a metal roof is pretty easy, but a few mistakes can undo your hard work.
- Skipping prep. If the roof isn't clean and dry, the coating won't stick and won't protect it the way it should.
- Counting coats instead of using the full amount. Everyone applies coats at a different thickness, so the number of coats varies. Use the full amount of coating your project calls for and keep applying until it's gone.
- Going too heavy on a sloped roof. Stick with thinner, even coats on steeper roofs so the coating doesn't drip while it dries.
- Mixing products. Pick MetalSafe Sealant or Color Roof Sealant and stay with it. Don't combine the two.
Keeping Your Metal Roof Waterproof
Once your coating is dry, check it for gaps or thin spots. A flashlight helps in darker areas. After that, inspect your roof once or twice a year, ideally after winter, and keep it clear of debris. Plan on a refresher coat in about 5 years.
Wrapping Up
MetalSafe Sealant and Color Roof Sealant are reliable, cost-effective ways to waterproof your metal roof. They protect it from rust and weather damage and improve the look of your home. And you can do the whole job yourself.
Ready to get started? Use our Metal Roof Kit Builder to get everything you need for your project. Have questions? Reach out to our Product and Application Support Team through our Contact Us page.
Metal Roof Waterproofing FAQs
Do I need to remove rust before waterproofing a metal roof?
Only the loose stuff. Wire-brush away loose, flaking rust and scale. MetalSafe Sealant can go right over light, tight rust with no primer. If you're using Color Roof Sealant, prime any rust spots with a water-based rust primer or converter first.
Can I waterproof a metal shed with Liquid Rubber?
Yes. MetalSafe Sealant works on aging metal roofs and metal structures, including corrugated tin sheds. Prep and coat it the same way you would a roof.
Can I change the color of my metal roof while waterproofing it?
Yes. Color Roof Sealant comes in nine color options. There's also a clear option if you want protection without changing how your roof looks.
Is sealing a metal roof the same as waterproofing it?
Pretty much. Both mean protecting your roof from water. Seam Tape and caulk seal the seams, cracks and fasteners, and the coating waterproofs the whole surface. A complete job does both.
