STI SpecSeal WF310

Latex based, high solids firestop caulk. Seals penetration openings in wood frame construction against the spread of fire, smoke and combustion byproducts. When exposed to elevated temperatures, WF300 expands rapidly to seal off voids left by the burning or melting of combustible materials.

Expands 5 times original volume
Will not shrink when dried
Adheres to common construction materials

SKU: 22969

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The STI SpecSeal WF310 is a professional-grade intumescent firestop caulk engineered specifically for wood frame construction. Unlike standard caulks that simply fill gaps, this latex-based sealant actively responds to fire conditions. When temperatures reach approximately 350°F, the material expands up to five times its original volume, sealing off voids left by melting plastic pipes or burning combustibles. This intumescent action maintains the fire barrier integrity of your rated assemblies when it matters most.

What sets the WF310 apart from general-purpose firestop sealants is its formulation for wood frame applications. Wood shrinks. Buildings settle. In seismic zones, structures move. The WF310 cures to a flexible membrane that accommodates these movements while maintaining its seal. The high-solids formula applies smoothly overhead without sagging, bonds aggressively to lumber and gypsum board, and won’t shrink or separate after drying. It’s water-based for easy cleanup during installation, yet fully water resistant once cured.

Tested to ASTM E814 (UL 1479) and CAN/ULC-S115, the WF310 is the basis for UL-listed firestop systems with ratings up to 2 hours. It’s also FBC System Compatible, meaning it’s been tested and approved for use with FlowGuard Gold, BlazeMaster, and Corzan piping systems.

Key Features

Intumescent Protection

Expands up to 5x volume at 350°F to seal voids left by melting or burning penetrants

UL Certified

Tested to ASTM E814 (UL 1479), CAN/ULC-S115, and ASTM E84; systems rated up to 2 hours

Flexible When Cured

Accommodates wood shrinkage, building settlement, and seismic movement

Installer Friendly

Water-based formula applies with standard caulking gun; cleans up with water before cure

Durable Finish

Water resistant and paintable when dry; won’t shrink, crack, or re-emulsify

Low Emissions

GREENGUARD Gold certified; 28 g/L VOC meets LEED v3 and SCAQMD Rule 1168

Electrical

CODE-COMPLIANT CABLE AND CONDUIT SEALING

Seals annular spaces around electrical conduit, wire bundles, and cable penetrations in fire-rated wood frame walls and floor/ceiling assemblies. Tested for use in UL-listed through-penetration firestop systems for electrical applications.

Plumbing

COMPATIBLE WITH COMMON PIPE MATERIALS

Firestops penetrations for copper, steel, PVC, CPVC, ABS, and PEX piping. FBC System Compatible with FlowGuard Gold, BlazeMaster, and Corzan systems. Ideal for sealing drain, waste, vent, and supply lines through rated assemblies.

HVAC & Mechanical

DUCTWORK AND MECHANICAL PENETRATIONS

Seals gaps around HVAC ducts, refrigerant lines, and mechanical penetrations in fire-rated wood frame construction. Works in head-of-wall joints and perimeter gaps detailed in tested firestop systems.

Retrofit & Maintenance

REPAIR AND RESEALING EXISTING INSTALLATIONS

Restores fire barrier integrity during tenant improvements, renovations, or maintenance work. Use to repair damaged firestop installations or reseal after adding or removing penetrants per original approved designs.

Frequently Asked Questions

What fire rating does WF310 provide?

The WF310 is the basis for UL-listed firestop systems with ratings up to 2 hours. The specific rating depends on the assembly type, penetrant, and installation details per the tested UL system.

Is this firestop caulk paintable?

Yes. Once cured, you can paint it to match surrounding surfaces. It’s also water resistant after drying and won’t re-emulsify.

Can I use it with plastic pipe?

Yes. It’s FBC System Compatible with FlowGuard Gold, BlazeMaster, and Corzan piping, and has been used successfully with PVC, CPVC, ABS, and PEX. Always verify compatibility with the pipe manufacturer for specific products.

What about electrical work?

The wet sealant is conductive until dry. Do not apply near exposed or energized conductors. Once cured, conductivity is no longer a concern.

How should I store it

Store between 40°F and 95°F. Shelf life is 24 months from manufacture date. Application temperature range is 35°F to 100°F.

What sizes are available?

WF310 is a 10.1 oz cartridge. Also available as WF320 (20 oz sausage) and WF305 (5-gallon pail).

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