Bond, Seal, and Protect: Choosing Aerospace Adhesives, Sealants, and RTV Silicones

Every aircraft is held together by chemistry as much as by fasteners. Structural adhesives carry load, sealants keep fuel and fire where they belong, and RTV silicones protect electronics from heat, moisture, and vibration. Bond, seal, and protect are the three jobs these materials do, and choosing the right product for each is a qualification decision, not a hardware-store substitution.

This guide walks through the three families featured in our July On-Demand lineup, what separates the chemistries, and how to match a product to the application. It is written for the engineers, MRO technicians, and procurement teams who need qualified materials with the documentation to back them.

Bond: Structural Adhesives

Structural adhesives distribute load across a joint instead of concentrating it at a fastener hole, which reduces weight, seals the bond line, and improves fatigue life. The right chemistry depends on the substrates, the load, and the service environment.

Epoxy Paste and Film Adhesives

Two-part epoxy pastes are the backbone of structural bonding, valued for high shear strength, environmental durability, and broad substrate compatibility. Film adhesives extend that performance to large bonded areas and honeycomb assemblies with controlled, consistent bond-line thickness.

• Loctite EA 9396 AERO A/B is a room-temperature-curing, two-part epoxy paste widely used for structural bonding and potting where elevated-temperature performance is required.
• 3M Scotch-Weld EC-2216 Gray B/A is a flexible, high-peel-strength epoxy known for toughness and vibration resistance across metals, composites, and plastics.
• Loctite EA 9658 NW AERO is a non-woven epoxy film adhesive for bonding and repair of composite and honeycomb structures where uniform bond lines matter.

Polyurethane Adhesives

Polyurethane adhesives bring flexibility and impact resistance where epoxies can be too rigid, making them a strong choice for dissimilar substrates and for bonding thermoplastics. The Uralane 5774-1 A/C and Uralane 5779-1 A/B systems are both qualified to Boeing BMS 5-105 and supplied in convenient 50 ml dual cartridges.

Thermoplastic bonding is a growing challenge as airframes adopt more of these materials, and it carries added pressure from tightening PFAS regulation. Huntsman's technical white paper reviews how the Uralane 5774-1 and 5779-1 systems support durable thermoplastic bonding while reducing PFAS regulatory risk. Download the thermoplastic bonding white paper to see the performance data.

Acrylic Structural Adhesives

Acrylic structural adhesives cure fast and bond well to a wide range of substrates with minimal surface prep. Click Bond CB200 is a two-part acrylic used with bonded fasteners and standoffs, letting technicians attach hardware without drilling holes that create stress risers and leak paths.

Explore the full range of qualified aerospace adhesives by chemistry and specification.

Seal: Aerospace Sealants

Sealants keep fuel contained, block fire and pressure paths, and protect joints from the environment. In aerospace they are qualified to demanding specifications because a sealant failure can ground an aircraft or worse.

Fuel Tank Sealants

Integral fuel tanks depend on polysulfide and related sealants that resist jet fuel, hold up to pressure and temperature cycling, and stay flexible for years. PPG PR-1440 B-1/2 is a two-part fuel tank sealant qualified to AMS-S-8802 and supplied in a Semkit for measured, waste-free mixing. Naftoseal MC-780 B-1 is a low-density fuselage and fuel tank sealant where weight savings matter.

Browse qualified aviation-grade fuel tank sealants by specification and cure profile.

Firewall and High-Temperature Sealants

Firewall sealants must maintain a fire and pressure barrier at sustained high temperature. Dapco 2200 is a primerless silicone firewall sealant that bonds directly to common firewall substrates, simplifying application while meeting firewall integrity requirements. See more qualified options on our aerospace sealants page.

Protect: RTV Silicones

Room-temperature-vulcanizing (RTV) silicones cure in place to a flexible rubber that protects electronics and assemblies from heat, moisture, vibration, and thermal cycling. They bond, seal, and insulate at once, which is why they appear across avionics, engine accessories, and electronic systems.

• Momentive RTV157 is a high-strength gray silicone adhesive sealant for high-temperature bonding and sealing.
• DOWSIL 3145 RTV is a clear, one-part adhesive sealant widely specified for bonding, sealing, and environmental protection of electronic assemblies.
• Momentive SnapSil RTV106 is a red, high-temperature one-part silicone that cures quickly and resists extreme heat.

One-part RTV silicones cure with ambient moisture and are ready to use straight from the cartridge, while two-part systems offer deep-section cure and faster throughput. Compare the full range of silicone adhesive sealants and silicone adhesives to match cure method and temperature rating to your assembly.

How to Choose Between Bonding, Sealing, and Protecting

Start with the function the joint has to perform, then narrow by substrate, environment, and specification.

• Need to carry structural load? Reach for a structural adhesive. Epoxy for maximum strength and rigidity, polyurethane for flexibility and thermoplastic bonding, acrylic for fast cure and bonded fasteners.
• Need to contain a fluid, gas, or fire? Reach for a sealant qualified to the governing spec, whether that is fuel tank integrity to AMS-S-8802 or firewall fire resistance.
• Need to protect electronics or absorb movement? Reach for an RTV silicone, matched to temperature rating, cure method, and dielectric requirements.
• Then confirm the spec. OEM and MIL specifications drive the final selection. Confirm the qualified product and packaging your program requires before you order.

Source Qualified Materials with the Documentation to Match

The difference between an industrial adhesive and an aerospace one is what you can prove about it. GracoRoberts supplies qualified adhesives, sealants, and RTV silicones with the certifications, inventory, and technical support required for OEM production and MRO operations.

Talk to our team to confirm qualification status for your platform, or review our certifications and quality page for documentation details.

Aerospace Adhesives and Sealants FAQs

What is the difference between an adhesive and a sealant?

An adhesive is formulated to bond substrates together and carry load across the joint. A sealant is formulated to fill and close a gap, blocking the passage of fluids, gases, or fire. Some products, such as RTV silicone adhesive sealants, do both.

What is RTV silicone used for in aerospace?

RTV (room-temperature-vulcanizing) silicone is used to bond, seal, and protect electronic assemblies, connectors, and engine accessories. It cures to a flexible rubber that resists heat, moisture, vibration, and thermal cycling, and many grades provide dielectric insulation.

Which adhesive is best for bonding thermoplastics?

Polyurethane adhesives such as the Uralane 5774-1 and 5779-1 systems are well suited to thermoplastic bonding, offering flexibility and durable adhesion. Huntsman's thermoplastic bonding white paper reviews their performance and their role in reducing PFAS regulatory risk.

What specification governs aircraft fuel tank sealants?

Integral fuel tank sealants are commonly qualified to AMS-S-8802 (formerly MIL-S-8802), which defines the class, application life, and cure time. Always confirm the class and specification called out for your application.

Can I use an industrial adhesive or sealant on an aircraft?

No. Certified platforms require materials qualified to the governing OEM or military specification and supported by traceable documentation. An industrial equivalent is not approved unless it holds the required qualification.