When evaluating construction sealants, one specification appears repeatedly in project documents, technical data sheets and architectural drawings:

ASTM C920.

Many buyers mistakenly assume ASTM C920 is simply another quality certificate. It is not.

Instead, ASTM C920 is one of the world’s most recognized performance standards for elastomeric joint sealants. It establishes how a sealant should perform under movement, weathering, adhesion and durability tests—not what chemistry it uses.

Understanding ASTM C920 helps distributors recommend suitable products, contractors avoid premature joint failure, and engineers select sealants capable of surviving decades of building movement.

This guide explains ASTM C920 in plain language.

What Is ASTM C920?

ASTM C920 is the Standard Specification for Elastomeric Joint Sealants, published by ASTM International.

Rather than specifying silicone, polyurethane or MS polymer chemistry, the standard evaluates performance.

A sealant meeting ASTM C920 has demonstrated acceptable performance through standardized laboratory testing including:

• Joint movement capability
• Adhesion after aging
• Elastic recovery
• Weather resistance
• Durability
• Low-temperature flexibility
• Cyclic movement performance

Because it evaluates performance instead of chemistry, different sealant technologies can comply with ASTM C920 if they pass the required tests.

Why ASTM C920 Matters

Modern buildings constantly move due to:

• Thermal expansion
• Wind loads
• Structural settlement
• Traffic vibration
• Seismic activity
• Material shrinkage

A sealant that cannot accommodate movement eventually experiences:

• cracking
• cohesive failure
• adhesive failure
• water leakage
• façade staining
• costly maintenance

ASTM C920 provides a common engineering language that allows architects and contractors to compare products objectively.

Understanding ASTM C920 Classification

ASTM C920 identifies sealants using four primary categories.

Category	Meaning	Example
Type	Number of components	Type S (single-component)
Grade	Flow characteristics	Grade NS
Class	Joint movement capability	Class 25 / 35 / 50
Use	Intended substrates or applications	Use NT, M, G, A, O

Type: Single or Multi-Component

Type S

Single-component sealants.

Advantages:

• Ready to use
• No mixing errors
• Faster installation
• Lower labor cost

Common examples include:

• Neutral cure silicone
• MS polymer sealants
• One-component polyurethane

Most construction weatherproof sealants belong to this category.

Type M

Multi-component sealants.

Advantages:

• Controlled curing
• Suitable for factory production
• Preferred in some structural glazing applications

They require accurate mixing before application.

Grade: Non-Sag or Self-Leveling

Grade NS (Non-Sag)

The most common construction grade.

Suitable for:

• Vertical joints
• Curtain walls
• Window perimeters
• Wall joints
• Facades

The sealant remains in place without flowing.

Grade P (Pourable or Self-Leveling)

Designed for horizontal joints.

Typical applications include:

• Parking decks
• Pavements
• Airport runways
• Bridge joints

Class: Movement Capability

The movement class is often the most important specification.

It indicates how much expansion and contraction a cured sealant can tolerate while maintaining adhesion.

ASTM Class	Joint Movement
Class 12.5	±12.5%
Class 25	±25%
Class 35	±35%
Class 50	±50%
Class 100/50	Special applications

Example:

A 20 mm joint using a Class 50 sealant can repeatedly move between:

• 10 mm expansion
• 10 mm compression

without failure.

Higher movement capability generally means longer service life in dynamic joints.

Understanding ASTM C920 Use Designations

The “Use” designation identifies suitable substrates.

Use	Suitable Materials
NT	Non-traffic joints
T	Traffic joints
M	Mortar
G	Glass
A	Aluminum
O	Other approved substrates

Many premium construction sealants carry multiple use classifications.

Which ASTM C920 Class Should You Choose?

Class 25

Suitable for:

• Residential windows
• Standard façades
• Interior movement joints

Typical movement:

Moderate.

Class 35

Recommended for:

• Curtain walls
• Commercial buildings
• Large façade systems
• High-rise construction

Offers increased safety against thermal movement.

Class 50

Designed for demanding applications:

• Seismic zones
• Expansion joints
• Super-tall buildings
• Bridges
• Infrastructure

Class 50 sealants provide the highest commonly specified movement capability.

Typical Applications by ASTM C920 Class

Application	Recommended Class
Residential windows	Class 25
Curtain wall perimeter	Class 35
Expansion joints	Class 50
Bridge joints	Class 50
Seismic buildings	Class 50
Precast concrete	Class 35–50

ASTM C920 Does Not Specify Chemistry

One common misconception is that ASTM C920 requires silicone.

It does not.

Products meeting ASTM C920 may include:

• Neutral cure silicone
• Polyurethane
• Silane-modified polymer (MS Polymer)
• Hybrid sealants

The standard evaluates performance, allowing engineers to select the chemistry that best suits the project requirements.

Selecting the Right Sealant for High-Movement Buildings

For projects involving large façade movement, infrastructure or curtain walls, movement capability becomes one of the primary selection criteria.

INGADA’s MS Weatherproof Sealant Series includes solutions engineered for demanding movement requirements:

Product	ASTM Movement Class	Typical Application
MS-625	Class 25	Precast panels, standard expansion joints
MS-635	Class 35	Curtain walls, bridges, seismic joints
MS-650	Class 50	Super-tall buildings, major infrastructure, high-movement joints

These products are designed with paintable, low-VOC, solvent-free MS polymer technology while targeting ASTM C920 performance requirements for weatherproof sealing applications.

Frequently Asked Questions

Is ASTM C920 mandatory?

Many commercial and infrastructure specifications reference ASTM C920 because it provides standardized performance requirements for elastomeric joint sealants. Whether it is mandatory depends on the project specification and local building codes.

Is ASTM C920 better than ISO 11600?

Neither standard is universally “better.” ASTM C920 is widely specified in North America and many international commercial projects, while ISO 11600 is commonly referenced in Europe and other regions. Many premium sealants are tested to both standards.

Does ASTM C920 guarantee long service life?

Compliance indicates that a sealant has passed standardized laboratory performance tests. Actual service life also depends on proper joint design, substrate preparation, installation quality, environmental exposure, and maintenance.

Does ASTM C920 only apply to silicone?

No. Silicone, polyurethane, MS polymer and other elastomeric sealants can all comply with ASTM C920 if they meet the required performance criteria.

Final Thoughts

ASTM C920 is more than a certification—it is a performance benchmark that helps engineers, contractors and distributors compare sealants on objective criteria such as movement capability, adhesion and durability. By understanding the standard’s Type, Grade, Class and Use classifications, specifiers can select products that match the real movement demands of façades, expansion joints and infrastructure.

For high-movement construction projects, choosing a sealant with the appropriate ASTM C920 class can significantly reduce maintenance risks and extend the service life of the joint.

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