When you strip away the outer layer of an aircraft, one thing you will be sure to find is sealant. During the manufacture and assembly of an aircraft, various sealants are used to protect key areas and components from corrosion, as well as exposure to high temperatures and chemicals such as hydraulic fluids and jet oils.
Aircraft sealants have different properties depending on the area of application they are designed for.
We maintain a diverse inventory for different purposes, including fuel tank sealants, fuselage sealants, access door sealants, window and canopy sealants and firewall sealants at Silmid.
Each aircraft sealant is also different in the way it cures. Information about curing for specific sealants may be found on the corresponding SDS/TDS.
Recent regulatory changes in the European Union have led to the phasing out of dichromate-cured aircraft sealant applications, with most manufacturers now opting to pursue manganese dioxide cured solutions that are REACH approved and safer for the user.
More often than not, sealant selection is driven by OEM specification. Major manufacturers such as Boeing, Airbus and Embraer have an approved list of sealants for each application based on rigorous testing, so it is important to ensure that the sealant choice you are making carries the correct approvals.
While selecting the right sealant is the first step, additional decisions need to be made that will affect the application of the sealant itself.
Sealants can generally be classified into 3 classes – A, B and C – although an S class does apply in some cases where a sealant can be sprayed.
Class A – Brush application, generally used on fasteners
Class B – Thicker consistency, used for fillet and injection seals
Class C – Thinner than Class B, used for fay sealing
Different aircraft sealant application times are important as the nature of the work being carried out will vary depending on application. Where there is a large surface to be covered, a longer application time is necessary to ensure that the first product applied does not cure before the application work has been completed. Shorter application times are essential for time critical work, where the seal needs to be almost immediate.
In MRO applications, cured aircraft sealant may need to be removed to allow access to all areas of the aircraft. Similarly, during manufacture, assembly and resealing applications, uncured or semi-cured sealants may need to be cleaned prior to releasing the part.
There are a number of accessories suited to the specific removal of aircraft sealant from Socomore and PPG Semco.
The packaging type will generally be concerned with two variables – volume of product required and the mixing process being used. Small volumes, for applications in multiple areas or by multiple users, are packaged into cartridge systems referred to as Techkits (manufactured by Techcon and generally used by 3M and Naftoseal) or Semkits (manufactured by Semco and used by PPG). These contain both the base and accelerator in one pack, and are mixed (either by hand or with the use of a mixing machine) using a piston rod sold as part of the kit.
For larger applications, or where a different mixing process is used, these products are supplied in separate tins (base and accelerator separate). These require closer attention to mixing ratios, as well as other application equipment including mixing sticks and dishes to hold the material).
PPG PR1440 B-1/2 150ml Semkit
3M AC-350 B-2 1USQ Kit
Naftoseal MC-650 Class B-1 130ml Techkit-130
Brand – The manufacturer who makes the specific sealant.
Product Number – This is the manufacturer’s name for the specific sealant product being used.
Class – This denotes the consistency of the product, and therefore the specific applications it should be used for.
Application Time – The length of time that the sealant is workable before curing.
Size – The volume of product contained in each pack.
Package Type – the type of packaging will determine the potential applications and mixing required.
An aircraft sealant plays a vital role in aviation safety, going far beyond simply bonding surfaces. These high-performance materials are engineered to protect critical components from corrosion, fluid intrusion, dust, and even fire spread—ensuring every flight meets rigorous safety and reliability standards.
Sealants also contribute to the structural integrity of the aircraft, reinforcing joints and surfaces subjected to constant vibration, pressure changes, and extreme temperature fluctuations. By selecting the correct sealants for aircraft, operators can significantly reduce long-term maintenance costs, prevent premature wear, and extend the service life of aircraft systems.
In addition to physical protection, aircraft sealants must comply with National Civil Aviation Authority regulations, meeting strict requirements for safety, durability, and environmental resistance. Their performance in high-stress zones—like fuel tanks, windshields, and engine compartments—is essential for maintaining airworthiness and reducing downtime.
The three most common types of sealant used in industrial applications are silicone, polyurethane, and acrylic. Each has unique properties suited for specific conditions. In aviation, however, polysulfide-based aircraft sealants are preferred due to their excellent fuel resistance and flexibility.
Sealants for aircraft are used in multiple areas including fuel tanks, access doors, windshields, canopies, firewalls, and fuselage joints. Their purpose is to provide protection from corrosion, leaks, vibrations, and temperature extremes.
Yes, most aircraft sealants are designed to fully cure within 72 hours under standard conditions. However, cure times may vary depending on the sealant class (e.g., Class A vs. Class B), application thickness, and environmental factors such as temperature and humidity. Always refer to the product's TDS for exact curing specifications.
Common causes of aircraft sealant failure include using expired materials, selecting the wrong sealant type for the application, and poor surface preparation. Ensuring proper cleaning, mixing, and adherence to OEM guidelines can help prevent these issues.
