Mike Wray
The right insulation can be a gamer changer!
Choosing the right fire resistant sealant is critical for maintaining fire compartmentation, achieving regulatory compliance, and protecting building occupants. Whether you are working on a commercial office, residential development, healthcare facility, or industrial project, selecting the correct firestop solution can significantly impact both safety and long-term building performance.
One of the most common questions specifiers and contractors ask is:
Should you use silicone or acrylic fire resistant sealants?
The answer depends on several factors, including joint movement, environmental exposure, substrate compatibility, and fire resistance requirements.
This guide explains the key differences between silicone and acrylic firestop sealants, where each performs best, and which top-performing products are available from National Insulation Supplies.
What Is a Fire Resistant Sealant?
Fire resistant sealants are passive fire protection materials designed to seal joints, gaps, and service penetrations in fire-rated walls and floors. Their primary purpose is to prevent the spread of:
- Flames
- Smoke
- Heat
- Toxic gases
These sealants help maintain the integrity of fire compartments during a fire event and are commonly tested to standards such as EN 1366 and BS 476.
Why Choosing the Correct Sealant Matters
Using the wrong firestop sealant can lead to:
- Failed fire inspections
- Reduced fire compartment performance
- Structural vulnerability
- Increased smoke spread
- Compliance issues
Modern buildings often contain moving joints, mixed substrates, HVAC systems, cable penetrations, and façade gaps that require specialised sealants with specific movement and durability properties.
Silicone vs Acrylic Fire Resistant Sealants
The two most widely used firestop sealant types are acrylic and silicone.
Acrylic Fire Resistant Sealants
Acrylic firestop sealants are water-based products designed for internal firestopping applications where moderate movement capability is required.
Advantages of Acrylic Sealants
- Easy to apply
- Paintable finish
- Cost-effective
- Excellent acoustic sealing
- Good adhesion to common construction materials
- Suitable for most internal linear joints
Limitations
- Less suitable for high-moisture environments
- Lower UV resistance
- Reduced flexibility compared to silicone systems
Best Applications
- Internal wall joints
- Cable penetrations
- Pipe penetrations
- Plasterboard systems
- Concrete and masonry joints
A popular acrylic solution is the Nullifire FS702 Intumastic Fire Resistant Acrylic Sealant 310ml, which offers up to 4 hours of fire resistance and up to 30% movement capability.
Silicone Fire Resistant Sealants
Silicone fire resistant sealants provide greater flexibility and durability, making them ideal for movement joints and external applications.
Advantages of Silicone Sealants
- Superior elasticity
- Excellent weather resistance
- UV resistant
- Long-term flexibility
- Better performance in damp conditions
- Suitable for dynamic joints
Limitations
- Typically higher cost
- Some products may require specialist paint systems
Best Applications
- Expansion joints
- Curtain wall systems
- Window and door perimeter seals
- External façades
- High-movement joints
- Damp or humid environments
The Nullifire FS703 Fire Resistant Silicone Sealant is widely used for linear joints and movement gaps, offering up to 4 hours fire resistance and excellent elasticity.
Acrylic vs Silicone Fire Sealants: Comparison Table
| Feature | ||
|---|---|---|
| Base Material | Water-based acrylic | Neutral cure silicone |
| Flexibility | Moderate | High |
| Movement Capability | Up to 30% | Up to 25% |
| Paintable | Yes | Limited depending on paint |
| UV Resistance | Moderate | Excellent |
| Moisture Resistance | Moderate | High |
| Internal Applications | Excellent | Excellent |
| External Applications | Limited | Excellent |
| Acoustic Performance | Up to 55 dB | Excellent acoustic sealing |
| Fire Resistance | Up to 4 hours | Up to 4 hours |
| Best For | Internal penetrations & joints | High-movement & external joints |
Key Factors to Consider Before Choosing a Firestop Sealant
1. Fire Rating Requirements
Always verify the required fire resistance period:
- 30 minutes
- 60 minutes
- 90 minutes
- 120 minutes
- Up to 240 minutes
Products like FS702 and FS703 are tested to EN 1366 standards for up to 4 hours fire resistance.
2. Joint Movement
Movement capability is one of the most important considerations.
- Acrylic sealants perform well in static or moderate movement joints.
- Silicone sealants are better for dynamic and high-movement applications.
3. Environmental Exposure
Choose silicone sealants for:
- External façades
- Weather exposure
- Wet environments
- UV-exposed joints
Use acrylic systems for controlled internal environments.
4. Acoustic Performance
Many firestop sealants also improve sound insulation.
The FS702 acrylic system provides acoustic sealing up to 55 dB.
5. Substrate Compatibility
Check compatibility with:
- Concrete
- Steel
- Masonry
- Plasterboard
- Aluminium
- Composite panels
Best Fire Resistant Sealants Available at National Insulation Supplies
Best Overall Acrylic Firestop Sealant
Nullifire FS702 Intumastic Fire Resistant Acrylic Sealant 310ml
The FS702 is ideal for internal construction joints, cable penetrations, and compartment wall systems. It provides strong acoustic sealing and can accommodate movement while maintaining fire integrity.
Key Features
- Up to 4 hours fire resistance - Tested to EN 1366-4, EN 1366-3 and BS 476 Pt 20-22
- Up to 30% movement capability (during fire test)
- Suitable for flexible walls and rigid walls & floors
- Used for sealing FB750 Intubatt
- Acoustics up to 55 dB
- Air tight up to 600 Pa
- Optifire® and Optifire®+ unique traceability identifiers
Best Silicone Firestop Sealant for Movement Joints
Nullifire FS703 Fire Resistant Silicone Sealant - All Types
A flexible fire-rated silicone sealant designed for high-movement joints, façade systems, and weather-exposed applications. FS703 is particularly effective in external joints and applications where flexibility and weather resistance are essential. Its UV resistance and long-term elasticity make it ideal for modern façade systems.
Key Features
- Up to 4 hours fire resistance - Tested to EN 1366-4
- Tested in gaps 10 - 220 mm
- Ideal for joints in rigid walls & floors, windows & door frames
- Airtight up to 600 Pa
- Superior elasticity
- Excellent tooling properties
- UV & weather resistance
- 25% Movement capability according to BS EN ISO 11600
- 20% movement when used with FJ203 as a weather seal
Best High-Expansion Intumescent Sealant
Nullifire FS702 Intumastic Fire Resistant Acrylic Sealant - All Types
FS702 Intumastic is a water-based acrylic sealant that cures to form a firm yet flexible fire seal. It is suitable for use in various construction joints, offering up to 30% movement capability while providing excellent acoustic and air sealing properties.
Product Comparison Table
| Feature | ||||
|---|---|---|---|---|
| Sealant Type | Acrylic | Silicone | Hybrid | Acrylic |
| Best Application | Internal joints | External & movement joints | Multi-purpose | Penetrations & joints |
| Fire Resistance | Up to 4 hours | Up to 4 hours | High-performance | Up to 4 hours |
| Flexibility | Moderate | High | High | Moderate |
| UV Resistance | Moderate | Excellent | Good | Moderate |
| Paintable | Yes | Limited | Usually yes | Yes |
| Acoustic Performance | Excellent | Excellent | Good | Excellent |
| Internal Use | Yes | Yes | Yes | Yes |
| External Use | Limited | Excellent | Good | Limited |
Installation Best Practices
To achieve proper fire performance:
- Follow tested system specifications
- Maintain correct seal depth and width
- Prepare substrates correctly
- Use backing materials where required
- Ensure compatibility with surrounding materials
- Avoid mixing untested systems
Incorrect installation can compromise compartmentation even when using certified products.
Conclusion
Choosing the right fire resistant sealant depends on your project’s fire rating requirements, movement conditions, environmental exposure, and substrate type.
- Choose acrylic sealants for internal, cost-effective firestopping applications.
- Choose silicone sealants for flexibility, weather resistance, and movement joints.
- Consider hybrid systems for multi-purpose modern construction applications.
Using tested and certified systems from trusted manufacturers such as Nullifire can help improve safety, compliance, and long-term building performance.
FAQs
1. What is the difference between acrylic and silicone fire sealants?
Acrylic fire sealants are best for internal applications and are usually paintable and cost-effective. Silicone fire sealants provide greater flexibility, UV resistance, and weather durability.
2. Which fire resistant sealant is best for movement joints?
Silicone firestop sealants are generally better for movement joints because they maintain flexibility over time.
3. Can fire resistant sealants be used outdoors?
Yes. Silicone and hybrid fire resistant sealants are commonly used for external applications due to their weather and UV resistance.
4. Are acrylic firestop sealants waterproof?
Most acrylic systems are water-resistant but are primarily intended for internal environments.
5. How long do fire resistant sealants last?
When properly installed, many firestop sealants provide long-term performance for the lifespan of the building system.
6. Do fire resistant sealants stop smoke as well as fire?
Yes. Many firestop sealants are designed to prevent both smoke and flame spread.
7. Are fire resistant sealants tested to industry standards?
Yes. Quality products are tested to standards such as EN 1366, EN 13501, and BS 476.