Waterproof sealant for metal: A handy guide

Get the facts on waterproof sealant for metal. Seams in metal roofing, siding, gutters, and other surfaces need periodic maintenance to stay leak-free. Save money by taking care of the job yourself. 

• Where and when to use waterproof sealant for metal
• How to use metal silicone sealant
• Best sealants for metal

Where and when to use waterproof sealant for metal

Highly durable and attractive, metal products are increasingly used in homes and businesses for roofing, siding, carports, storage buildings, and many other structures.

A key component of any metal system is the sealant between sheets or parts. If not properly sealed, leaks may develop around seams, joints, and fasteners, thus causing serious problems.

These areas have to be waterproof. This is generally done by using a waterproof sealant for metal. An excellent sealant will adhere permanently to metal and other surfaces, remain flexible, and resist drying out or cracking over time. Paintability is also a plus in many applications.

How to use metal silicone sealant

One of the most common types of sealant is metal silicone sealant. Silicone is highly waterproof, remains flexible, and adheres well. One drawback is that pure silicone is not paintable. However, paintable silicone blends are available.

Here are the steps to applying a silicone sealant, although the procedure is similar if you choose any of the other types of metallic sealants listed in the next section.

1. Always wear gloves and work in a well-ventilated area when using sealants.
2. Remove old sealant, rust, or loose paint with a scraper or putty knife and sandpaper.
3. Clean up by removing dust and dirt, then wipe the area to be sealed with mineral spirits to remove any greasy residue.
4. Using a caulk gun, apply the metal silicone sealant in an even bead along the seam or joint. Smooth out the sealant with a caulking tool or your finger.
5. Ensure that you have a continuous seal around the entire piece. Water can penetrate even the smallest gap.
6. Allow the waterproof sealant to completely cure before normal use or exposure to rain.

Best sealants for metal

While the most common metal sealant is silicone sealant, this is not your only option. Depending on the application, you may choose another waterproof sealant for metal with different characteristics.

Polyurethane metal sealants are paintable and can be a good choice. However, they are somewhat less resistant to UV light and extreme temperatures. This makes polyurethane less desirable for exterior projects.

Another option would be SMP (silane-modified polymers) sealant. SMP also forms a strong, waterproof bond to metal, but it is particularly elastic and abrasion resistant.

Epoxy can also be used as a waterproof metal sealant if you choose a compatible formula. Epoxy becomes extremely rigid when it cures and can fill large gaps without shrinking or cracking. It is also a strong adhesive. It will create a much stronger bond between two pieces of metal, or metal and an adjoining surface, than most other metallic sealants.

If your repair requires bonding capabilities, we recommend Loctite Epoxy Marine. This system consists of a resin and a hardener in a convenient dual syringe. Once mixed, a rigid, high-strength bond will form in 120 minutes. This epoxy will bond to metal, concrete, glass, pipes, wood, and most plastics, making it ideal for almost any repair project. This amazing adhesive will even cure under water, eliminating the need for the area to be dry before proceeding.

For small repairs, try Loctite Extreme Gel and have your job completed in just minutes. Due to its unique formula, this versatile glue can fill gaps and fuse many different materials. It stands up to vibration, impact, and UV light, and is water-resistant. Perfect for repairs indoors or out.