Like fasteners or other small components of a metal roofing system, sealant might not seem like a significant piece of the puzzle.
Even though you might not see the sealant, it’s a critical part of the roof system, especially as a secondary defense against water intrusion.
Beyond offering the metal sheet and coil used in metal roofing systems, Sheffield Metals also offers sealant and other metal roofing accessories — making us a one-stop shop for everything needed to install a standing seam metal roof. On top of that, sealant plays a huge role in the engineering of our profiles, which is why we think knowing about the different uses and types of sealant is important.
In this article, expect to learn:
- What sealant is
- The types of sealants
- Application methods and special characteristics of different sealants
- Key considerations to remember about sealant
What is Sealant?
At its base level, sealant is “a material used for sealing something to make it airtight or watertight.” Or, it may also be considered a product to seal a space or joint between two materials. Sealant is often mistaken for an adhesive, even though it’s typically not used to bind two items together.
However, the term “sealant” is a general word that covers a multitude of products used in a variety of industries and applications. Some of the most common uses for sealant include:
- HVAC systems
- Automotive and aerospace applications
- Concrete and cement
- Floors and windows
While sealants are often similar to one another, each type has its specific characteristics and uses to keep in mind. For this article, we’ll be discussing the sealants specifically used in standing seam metal roofing applications.
Types of Sealant Used in Metal Roofing Systems
For metal roofing, there are two main types of sealant used regularly: gun caulking sealant and tape sealant. Let’s break down these two types and explain the characteristics and uses for each one.
Gun Caulking Sealant
This type of sealant typically comes in a tube that is loaded into a caulking gun. From there, the sealant can be applied accordingly to the metal roof system, which is typically outlined in the manufacturer’s installation details.
Gun caulk sealant is made from a few different materials, including:
- Silicone (may also be referred to as an “oxime-cured silicone sealant”)
For the most part, these materials are equal in their own right and work well in architectural metal roof and wall applications.
Also, you may notice that some sealants are referred to as one- or single-component sealants, meaning they’re composed of one base component and don’t need to be mixed with anything before application. This is especially helpful for metal roofing because it allows the installer to apply the sealant on the fly without interruption.
Curable vs. Non-curable Sealants
There are two distinct types of caulking sealants: curable and non-curable.
Curable - Curable sealants some out of the tube as a thick paste-like substance and will become harder and more rigid as it cures. For example, NovaFlex Metal Roof Sealant has a standard timetable related to curing:
- 5 days (40°F/60% relative humidity)
- 48 hours (75°F/50% relative humidity)
Non-curable - Non-curable gun caulking sealants don’t harden over time and remain wipeable for a specific period of time. For example, a hot-melt sealant is non-curable, which makes it more flexible and easier to use on a mechanically seamed metal roof profile where seaming is required.
Gun caulking sealants come in a wide variety of colors that match the colors of most paint system brands, such as Sherwin-Williams, PPG, or other coil coating suppliers. Or, many installers choose to use a clear sealant, as it works well on any color of a metal roof or wall application.
When to Use Gun Caulking Sealant
There are some specific metal roof installation situations where you will need to use a gun caulking sealant. Some scenarios may include:
- Any point where you have a metal-to-metal connection that's isn’t fastened off (i.e., z-closure sides).
- In between the panel seams.
- In spots where the metal is lapped, such as ridge caps, sidewalls, headwalls, metal flashing, and trim.
- At the top of a pipe boot, which should also include a pipe band to keep it from sagging.
- As a method to stop any anti-siphoning by the eave, which can happen as water runs down the roof and gets sucked up between the seams.
When NOT to Use Gun Caulking Sealant
While there are specific use cases for sealant, there are also scenarios where gun caulk is not recommended, such as:
- Points on the roof where metal could be used in the sealant’s place, such as flashing areas.
- In spots where the sealant is exposed, as it will eventually fail (especially in places of regular UV exposure).
- On or at gaps or voids in the roof system.
- On top of any fasteners.
It’s important to remember that using a sealant is not a “cure-all.” It’s meant to be a secondary defense and shouldn’t be the only component that keeps the roof system from leaking.
Testing & Standards
Sealants are tested and engineered to adhere to a variety of industry standards, which provides realistic expectations for how the product will perform once installed. While the test methods and specific guidelines may vary between different products, let’s run through a few common standards:
- Tensile strength (ASTM D412)
- Elongation (ASTM D412)
- Tear resistance (ASTM D624)
- Shore hardness / Durometer hardness (ASTM D2240)
- Joint seal designation (ASTM C920)
- Adhesion to glass, aluminum, and vinyl (ASTM D903)
- Adhesion and cohesion (ASTM C719)
- Federal Specification TT-S-001543A: “This specification covers the properties of a single-component, cold-applied silicone rubber base joint sealing compound (joint sealant) for sealing caulking and glazing applications in building areas and other types of construction.”
- Federal Specification TT-S-230C: “This specification covers the properties of a single component cold-applied synthetic rubber base joint sealant, chemically curing type, for sealing, caulking, or glazing application in buildings and other types of constructions.”
In addition to the specific requirements that the sealant itself must meet, gun caulking sealant also plays a part in the testing of entire metal roofing systems. For example, in the standard ASTM E2140 Water Submersion test, mechanically seamed panels with a low-slope are seamed together and then completely submerged under six inches of water for approximately six hours. Then, static water pressure is applied to the outside face of the roof panel, which tests the roof’s ability as a water barrier. This method evaluates the water barrier (not water-shedding) of hydrostatic roof systems with a pitch below 3/12.
The other significant category of sealant is tape sealant, otherwise known as butyl tape. This double-sided tape sealant comes in rolls of various sizes of thicknesses, beads, and widths. According to Triangle Fastener Corporation, butyl tape sticks to a variety of materials, including metal that has a PVDF (Kynar®) or SMP paint system.
As the name suggests, butyl tape is made from butyl, a synthetic rubber composed of the copolymer of isobutylene with isoprene.
Butyl tape is a flexible sealing material that won’t harden, doesn’t bleed or stain, and works well for nearly every type of roof application.
How to Apply Tape Sealant
Butyl tape creates a seal when met with compression.
For example, with a z-closure, there’s the base metal, then the butyl tape, and then another piece of metal. Once all three layers are together, the materials are compressed when fastened off every four inches on center. The last part of every four inches is critical because when you put a fastener through butyl tape, it compresses it out two inches on each side.
When to Use Tape Sealant
Butyl tape is used as the sealing material for the following installation situations:
- Metal-to-metal applications where the metal will be fastened off or screwed down.
- Anytime you have a z-closure (bottom)
- Anytime you have an offset cleat (bottom)
- Underneath a pipe boot, as it will be fastened down to the metal panel.
When NOT to Use Tape Sealant
There are also spots where it’s not suitable to use butyl tape, including:
- Whenever you’re not fastening or screwing down anything.
- On the sides of z-closures.
- Anywhere there isn’t compression that creates a seal for the butyl tape.
- In between panel seams, as butyl tape is too thick and does not allow a mechanically seamed profile to be double-locked (180 degrees).
Testing & Standards
Like gun caulking sealant, butyl tape goes through testing that it must adhere to or pass. Again, these test methods are brand-specific and may vary between manufacturers, but here are some common tests you might come across for butyl tape:
- Sag (AAMA 800)
- Elongation (ASTM C908)
- Peel adhesion (ASTM D3330)
- Tensile adhesive strength (ASTM C907)
- Specific gravity (ASTM D792)
- Staining - Will it stain a painted or unpainted surface? (ASTM D925)
- Water penetration / static water pressure (ASTM E2140)
Additionally, many butyl tapes are tested to meet Military and Federal Specifications. Check with your supplier if specific testing requirements are needed.
Considerations to Keep in Mind For Metal Roof Sealant
#1: Sealant is a secondary defense against water, not the primary defense.
The reason that sealant is added to a metal roof or wall system is to act as a secondary defense against water intrusion at flashing spots, laps, and penetration points. By no means should it ever be the first line of defense that keeps the roof from leaking.
#2: You shouldn’t see the sealant if you’re looking at the roof or wall.
Going along with the fact that sealant is not the first thing that keeps water out, you also shouldn’t be able to see the sealant if you’re looking at the roof. If you see sealant, it means the metal (the more reliable and durable material) isn’t the first thing water, UV, or other damaging elements will touch. Also, another red flag of improper sealant use is if you see big globs of it at any spot on the roof.
#3: Refer to the manufacturer’s installation details as to how and where the sealant should be installed.
Manufacturer’s installation details exist to give installers detailed drawings and instructions on how the components of a metal roof come together for installation. Sealant uses and recommendations are clearly outlined in most installation details. For some examples of where sealants or butyl tape are visible on a detail, take a look at the SMI 1.5” SnapLock 550 Plywood Installation Details.
#4: Make sure the sealant you’re using is directed by the manufacturer of the system or, at minimum, is designed for a metal roof or wall with specific paint finish.
As discussed earlier, sealant is a blanket term that consists of many different types for a variety of uses. It’s critical to make sure that the sealant and butyl tape you’re using is explicitly formulated for painted metal roof and wall panels. On top of that, make sure to verify that it’s compatible with the paint system, such as PVDF, SMP, or otherwise, as incompatible materials could lead to premature degradation, among other metal roof problems.
#5: If you’re caulking vertically, you might need to go back for a second time after it’s cured.
This consideration is specific, but it’s something we frequently see on projects. Vertical caulking is subject to stronger gravity than horizontally-applied sealant, and therefore might sag down before it cures. Make sure you’re aware of this and check to see if you need to go over it a second time.
Final Thoughts on Sealant
As you can tell, sealant is an integral part of a standing seam metal roof system, which is why knowing the specific use cases for both gun caulking sealant and tape sealant is helpful.
- Always make sure you’re using sealant specifically designed for painted metal panels.
- Sealant for the most part should not be overly visible or caked on.
- Do not use sealant as the primary defense against water intrusion.
- The best way to make sure you’re correctly using sealant is to verify with the manufacturer’s recommended installation details.
Sheffield Metals has spent nearly 25 years building a product line designed for architectural metal roofing and wall projects — including the gun caulking and tape sealants described in this article. We’ve partnered with reputable manufacturers, like NOVAFLEX and Triangle Fastener Corporation, to provide the high-performance sealants you need for your metal roof or wall application.
Contact us today to discuss your sealant needs with one of our knowledgeable metal roofing specialists!