Choosing an aerospace corrosion-inhibiting sealant

The short answer

A corrosion-inhibiting sealant seals a joint and carries an inhibitor that protects the metal inside it. A corrosion-inhibiting compound is a thin displacing fluid or film sprayed into cavities and lap joints — it protects, but it does not seal. A corrosion-inhibiting primer is a coating layer that goes under paint. They solve overlapping problems in completely different ways, and specifying one where the manual calls for another is a common and expensive error.

The three families, and what each is actually for

Sealants do structural or environmental work. They fill and seal a joint — a fay surface, a fillet, a fuel tank seam, a windshield edge — and stay flexible through thermal cycling. The corrosion-inhibiting versions add a pigment that passivates the metal in the joint. This is what you want where two dissimilar metals meet, or anywhere moisture can sit in a seam.

Corrosion-inhibiting compounds (often written CIC) are thin, penetrating and usually soft-film. They creep into a lap joint or a closed cavity you cannot seal, displace water and leave a protective film. They are maintenance products, reapplied on a schedule — not a permanent seal, and not structural.

Primers are part of the paint system. A corrosion-inhibiting primer bonds to prepared metal and puts an inhibiting layer under the topcoat. It protects a surface; it does not fill a gap.

The test that separates them in practice: is there a gap to close, a cavity to flood, or a surface to coat? Those three answers map to the three families.

Reading the class code on a sealant

Polysulfide sealants are usually ordered with a suffix such as B-2 or B1-2. It is not a catalogue code — it describes how the product is supplied and how long you have to work with it.

• The letter is the class, which governs consistency and application method. Broadly, the

brushable and sprayable grades sit in one class and the extrudable fillet and fay-surface grades in another.

• The number is the application life in hours — roughly how long the mixed material stays

workable.

So two tins with the same base number and different suffixes are the same chemistry with different handling. Pick the class from how you are applying it and the application life from how long the job takes; a two-hour material on a job that needs four is wasted material and a bad joint. Confirm the exact class and application life against the product datasheet — the convention is general, the numbers are product-specific.

Chromate or non-chromate

Traditional corrosion-inhibiting sealants and primers used chromate pigments, which work extremely well and are hexavalent-chromium based. Regulatory pressure has pushed the industry steadily toward non-chromate alternatives, and most sealant families now offer both — you will see products explicitly labelled non-chromate alongside their chromated equivalents.

Two practical points. First, the two are not drop-in interchangeable: the approval on your maintenance documentation is for a specific product, and a non-chromate substitute needs its own approval. Second, if you operate into or out of Europe, check the regulatory position before you standardise on a chromated product for the long term.

What to specify when you order

• The spec, not the brand. Aerospace sealants are ordered to a specification; the brand is

what satisfies it. Send the spec and the class.

• The class and application life — B-2 and B1-2 are different orders.
• Cure and storage state. Many of these ship frozen or with a limited shelf life, and the

remaining life on arrival is a real acceptance criterion.

• Batch documentation. For a shelf-life-limited material, the batch and its dates are the

whole point of the paperwork.

Frequently asked

Is a corrosion-inhibiting compound a substitute for sealant?

No. A compound protects a joint it can penetrate; it does not seal one. Where the manual calls for a sealed joint, a compound will not deliver it.

Can I use a fuel tank sealant as a general-purpose sealant?

Fuel tank sealants are formulated for continuous fuel immersion, which is a harder requirement than most joints need. It is usually the wrong economics rather than the wrong chemistry — but the approval still has to cover the application.

Why does the same sealant appear with several suffixes?

Same chemistry, different class and application life. Choose by how you are applying it and how long you need to work.

How is shelf life handled on arrival?

Ask for remaining shelf life on the quote, not just at delivery. For frozen materials the cold chain matters as much as the date, and both should be documented.

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Sourcing corrosion-inhibiting sealants, compounds or primers? Angad Aviation sources sealants, corrosion-inhibiting compounds, conformal coatings and primers from the manufacturers maintenance teams already specify — including non-chromate grades — with batch documentation and traceability. Browse sealants, coatings and chemicals & consumables, or send us a spec and class and we will quote it.