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Fire barrier caulk: top picks
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Best overall 3M3M Fire Barrier CP 25WB+ Caulk
Intumescent caulk that expands up to 8x when exposed to heat, providing excellent fire and smoke seal for through-penetrations. Water-based, low odor, and easy to apply.
- Excellent fire resistance
- Low odor, water-based
- Easy to apply and clean up
- Requires thick application for deep gaps
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Best for high-traffic areas HILTIHilti CP 671 Firestop Acrylic Sealant
Durable, paintable acrylic sealant with high flexibility. Suitable for dynamic joints and penetrations, tested for air leakage and smoke.
- High flexibility
- Paintable and durable
- Good for dynamic joints
- Slightly longer curing time
- Higher price point
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Best value TremcoTremco Tremstop 6A Acrylic Firestop Sealant
Affordable acrylic latex firestop sealant with UL classified ratings for various penetrations. Easy application and cleanup with water.
- Cost-effective
- UL classified
- Easy water cleanup
- Less flexible than silicones
- Not for large gaps
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Best silicone sealant USASEALINGSTI SpecSeal 40-21 Silicone Firestop Sealant
Premium silicone firestop sealant with high elongation and adhesion. Ideal for joints and penetrations requiring flexibility and movement capability.
- High flexibility and movement
- Excellent adhesion
- Long service life
- More expensive
- Requires primer on some surfaces
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Best for electrical boxes RectorsealRectorseal Fire Barrier Putty Pads
Pre-formed intumescent putty pads for electrical outlets and switch boxes. Easy to install behind cover plates to maintain fire rating.
- Simple peel-and-stick installation
- No mixing or curing
- Effective for small cavities
- Limited to specific applications
- Not a general caulk
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Best for irregular gaps 3M3M Fire Barrier MP+ Moldable Putty
Moldable putty that can be shaped by hand to seal irregular penetrations and voids. Re-enterable for future cable changes.
- Highly moldable
- Re-enterable
- No drying time
- Not paintable
- May sag if too thick
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Best budget pick HILTIHilti CP 620 Firestop Acrylic Sealant
Economical acrylic sealant with UL listings for common penetrations. Good for interior use where moderate flexibility is needed.
- Budget-friendly
- UL listed
- Low VOC, water-based
- Less movement capability
- Not for exterior use
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Best for high-movement joints SpecSealSpecSeal Series SS2001 Silicone Firestop Sealant
Two-part silicone sealant with +100% movement capability. Designed for seismic and high-flexibility joints in fire-rated assemblies.
- Extreme movement capacity
- Fast cure time
- Excellent durability
- Expensive
- Requires mixing gun