A Complete Guide to A, B & C Classes in PPG Aerospace Sealants

• PR1440 B2
•  PS870 B1/2
•  PR1440 A2
•  PR1776 C12

Understanding the Letter: A vs B vs C (Sealant Class)

The letter designation is commonly referred to as the sealant class.

It defines the consistency (viscosity), flow characteristics, and intended application method of the material once mixed.

A-Class – Brush / Fay Sealing Grade

A-Class sealants are:

•  Lower viscosity
•  Brushable
•  Designed to wet surfaces easily
•  Capable of forming thin, uniform films

Typical applications:

•  Fay sealing between structural components
•  Lap joints
•  Internal structural sealing
•  Pre-assembly sealing before fastener installation

If the sealant needs to spread easily across mating surfaces, A-Class is typically specified.

B-Class – Fillet / Non-Sag Grade

B-Class sealants are:

•  Paste-like consistency
•  Non-slump / non-sag
•  Applied via Semkit cartridges or bulk kits
•  Designed to hold bead or fillet shape

Typical applications:

•  Aircraft fuel tank sealing
•  External fillet bead
•  Rivet encapsulation
•  Gap filling
•  Heavy maintenance checks

This is the most commonly used sealant class in aerospace MRO.

C-Class – Self-Levelling / Flowable Grade

C-Class sealants are:

•  Very low viscosity
•  Self-levelling
•  Designed to flow into cavities and channels

Typical applications:

•  Integral fuel tank channels
•  Complex structural geometries
•  Areas where gravity flow improves penetration

If the sealant needs to flow into tight areas rather than hold a bead, C-Class is typically required.

Understanding the Number: 1/4, 1/2, 1, 2, 12, 24

The number refers to application life (work-life) at standard laboratory conditions (typically 25°C).

Application life = how long the mixed material remains usable.

Short Work-Life Variants

These are ideal when:

• Small repair areas are involved
•  Fast turnaround is required
•  Technicians are working in defined sections

B1/4 and B1/2 variants are common in AOG maintenance.

Medium Work-Life Variant

This is one of the most widely used options in heavy maintenance.

A B2 sealant allows:

•  Larger sealing areas
•  More controlled application
•  Reduced technician time pressure

Extended Work-Life Variants

Typically used in:

• Aircraft production lines
•  Large structural assemblies
•  Major fuel tank builds

These provide:

• Long operational windows
•  Multi-shift usability
•  Reduced material waste in large assemblies

Less common in routine MRO, but essential in OEM manufacturing.

Temperature Impact (Often Overlooked)

Work-life ratings are based on controlled laboratory conditions (~25°C).

In real-world hangars and production environments:

• Higher temperatures reduce working time
•  Lower temperatures extend working time

For example:

A B1/2 applied in a hot hangar may behave closer to a B1/4.

Correct variant selection is especially important for global operators working across varied climates.

Practical Example

For a typical corrosion-inhibitive fuel tank sealant:

• B1/2 → Small tank repair
•  B2 → Larger panel reseal
•  C12 → OEM channel sealing
•  A2 → Structural mating surface sealing

The core chemistry remains the same — but handling characteristics differ significantly.

Why the Suffix Matters

Selecting the wrong class or work-life can result in:

• Premature curing before job completion
•  Material waste
•  Rework and repeat labour
•  Reduced efficiency
•  Delayed aircraft return-to-service

In aerospace maintenance, labour cost and downtime typically exceed material cost, making correct selection critical.

Final Summary

When reviewing a PPG aerospace sealant code:

Letter (Class) = Consistency and application method

• A = Brushable / fay sealing
• B = Non-sag / fillet sealing
•  C = Self-levelling / flowable

Number = Application life

• 1/4 → ~15 minutes
• 1/2 → ~30 minutes
• 1 → ~1 hour
• 2 → ~2 hours
• 12 → ~12 hours
• 24 → ~24 hours

The suffix is not a minor detail — it determines how effectively the sealant can be applied and managed in real maintenance or production environments.

Supporting Aerospace, OEM & MRO Operations

At ConRo, we support aerospace operators and manufacturers with:

• Correct sealant class and work-life selection
•  Batch traceability and certification
•  Shelf-life visibility (DOE displayed online)
•  Same-day despatch where stock is available
•  Global hazardous and temperature-controlled shipping

If you're reviewing sealant specifications or optimising material selection, our technical team can assist.

info@conro.com
+44 (0)208 953 1211
www.conro.com

ConRo — Where Precision Meets Delivery.