How to Waterproof a Metal Roof? Steps, Tools and Products

Written By Adam Paul - Waterproofing Expert

A metal roof can be waterproof by following the below 7 steps successfully in order to prevent water leaking from roof joints, seams, screw holes, panel connections, valleys, and flashings. 

7 Steps to Waterproof a Metal Roof

1. Clean the metal roof
2. Tighten the loose fasteners
3. Power wash the metal roof surface
4. Seal the gaps and loosen the metal roof
5. Waterproof the metal roof valleys
6. Waterproof the metal roof flashings
7. Apply the waterproofing layer and coatings

You should use essential tools and instruments, and recommended products for waterproofing the metal roof. A metal roof can be damaged due to hit by physical force, cut using sharp objects, spread of corrosive substances, and temperature fluctuations. 

These damages can cause wear, tear, and loosening the waterproofing membrane on the metal roof. Hence you should apply suitable waterproofing sealant, coaitng on the metal roof. Not only should you waterproof metal roofs, but you should also ensure waterproofing for concrete roofs using a recommended method.

7 Steps to Waterproof the Metal Roof?

You should follow the below 7 steps to waterproof the metal roof.

1. Clean the Metal Roof

Before starting metal roof waterproofing, you should clean the top of the metal roof using a broom to remove leaf litter, dust and other hard debris on the metal roof. You should clean the metal roof valley and flashing to remove all the solid debris on the surface.

2. Tighten the Loose Fasteners

After cleaning the metal roof, you should make sure to tighten, add, or replace all loose fasteners on the roof. Tightening the fasteners will prevent unwanted movement between roofings that can lead to potential leaks after waterproofing the roof.

3. Power Wash the Roof Surface

Next, clean the roof surface to remove any loose or flaking material. Because of flaking materials, any dust or debris left on the surface can reduce adhesion between the roof surface and the waterproofing layer. Hence, the strongest recommendation is power washing for larger areas. You can use acetone for smaller surfaces.

4. Seal the Gaps and Loosenings on the Metal Roof

After the power washing, you can clearly see visible damages such as corrosion areas, loosening nuts and screws, opened seams and joints, and loosening holes and joints. 

You should use seam tape to seal all gaps greater than 1/8 of an inch. When applying the seam tape on the gaps of a roof, you should not pull or stretch it. You should allow the tape to fall onto the surface and then apply pressure with a roller to increase adhesion. 

You can use metal-safe caulking gel to seal the gaps less than 1/8 of an inch. After metal safe gell is applied on the metal roof surface, you should tool down using a brush to ensure a smooth surface and complete coverage. You should seal all the seams around vents, flashings, and protrusions properly using seam tape before applying the overall coating.

5. Waterproof Metal Roof Valley

You should waterproof the metal roof valleys and flashing to improve the water protection from the roof. You should keep more than 6 inches under the top running panel of the roof valley. If the roof is large and has a lower inclination, you should use a recommended sealant or tape between the valley panel and the top water running panel of the roof. 

You should use a screw seal for the screws.

You should not place the screws close to the valley. When the water is flowing on the valley, it can leak through the screws.

6. Waterproof Metal Roof Flashing

If the old flashing has been damaged and leaked, you should install flashing on the metal roof when it meets the walls. You should follow the below 8 steps to waterproof the flashing. 

1. Clean away the old flashing and tar
2. Fasten ferrying stripes to hold the screws
3. Fasten the spacers temporarily to get the right height
4. Set the trim at the correct height and mark the brick where you need to cut
5. Cut the bricks using a masonry blade
6. Clean the dust and start flashing from the widest point
7. First, mark and cut the flashing from the end wall, then side walls, and later, the top of the wall. Keep the flashing space at least 5” from the wall. You should test everything before caulking.
8. Finish the fashing from bottom to top and caulking. 

7. Apply the Waterproofing Layer on the Metal Roof

After sealing all the damages, roof valley and flashing you should apply the waterproof sealant on the metal roof. You can apply a waterproofing layer directly on the light rust metal roof without priming or sandblasting. Small metal roofs can be applied to a waterproofing layer using a brush. But for the larger metal roofs, you can use a spray system to increase the speed and efficiency. 

You can apply a liquid rubber topcoat for reflectivity or if a specific color is required or desired. You should always allow proper drying time for the prepared areas before applying the next coating. The Metal Safe sealant will turn from brown to black when it's dry. Keep in mind that using excess material during the application will prolong drying time.

What Tools and Materials are Needed for Metal Roof Waterproofing?

Safety Tools - Gloves, Helmet, Safety harness (if working at heights), Non-slip shoes

1. Power tools: Screwdriver (manual or electric), Circular saw (for cutting metal panels if needed)
2. Sealant application tools: Caulking gun, Putty knife or spatula for spreading sealant
3. Roofing nailer - Pneumatic or cordless roofing nail gun for fastening metal panels securely on the roof
4. Metal shears: For cutting metal sheets or panels to fit specific areas on the roof
5. Corrosion-resistant screws: Corrosion-resistant screws designed for metal roofing applications
6. Measuring tools: Tape measure, and Level
7. Brushes and rollers: Applicators for applying primers, coatings, or sealants on the metal roof surface
8. Pressure washer: To clean the metal surface before applying waterproofing materials on the metal roof
9. Roofing membrane or underlayment: Depending on the specific waterproofing method, you may need a roofing membrane or underlayment material.
10. Ladder or scaffolding: Depending on the height and structure of the roof, a ladder or scaffolding may be necessary for access.
11. Cleaning supplies: Rags or sponges for metal roof cleaning surfaces
12. Solvent or cleaner for removing dirt, grease, or old sealant
13. Roofing adhesives: Adhesives compatible with metal roofing materials for securing seams and joints.
14. Flashing materials: Metal flashing to reinforce vulnerable areas like valleys and joints.

What Waterproofing Products can be Used for Metal Roof Waterproofing?

You can use these 7 most used and recommended waterproof products for metal roof waterproofing. Before you use these products, you should pay attention to the manufacturer's guidelines. 

How to Damage a Metal Roof?

A metal roof can be damaged due to these main 4 reasons.

1. Applying a physical force: The metal roof can be damaged by physical force. Due to the physical forces on the roof, the panel can bend, and water will not be removed properly from the floor. Over time, bending or damaged areas can rust easily.
2. Using a sharp objects: Use sharp tools such as knives or screwdrivers to scratch or puncture the surface of the metal roof.
3. Apply corrosive substances: Apply corrosive substances such as acids or strong chemicals to the metal roof, which can cause it to corrode and weaken over time.
4. Expose to extreme temperatures: Expose the metal roof to extreme heat or cold, which can cause it to expand or contract rapidly, leading to potential damage.

Is Concrete Roof Better than Metal Roof?

A concrete roof is not better than a metal roof when considering the waterproofing of the roof. Concrete roof waterproofing needs expert knowledge, time and money. But a metal roof can be waterproofed more easily than a concrete roof. More than that, metal roofs are lightweight, easy to install, have longer lifespans, and are easier to maintain than concrete roofs. 

But you can waterproof the concrete roof using this step-by-step guide. The Aqviz team has included all detailed tools, methods, products, tips, and tricks about concrete waterproofing in this guide. You can reach us before you start your DIY concrete roof waterproofing project.