323 GAP SEAL FR 300X300

    323 K-NRG Gap Seal FR™

    KARNAK K-NRG Gap Seal FR is a fire resistant, building envelope sealant designed to seal joints, penetrations and transitions when applied to above-grade wall assemblies.  It is a single-component, water-based acrylic mastic that cures to a tough monolithic elastomeric-like membrane.  This sealant is fully compatible with K-NRG Seal VP™.

    Passes stringent NFPA 285 Fire Test.

    Available in 3.5 gallon buckets and 30 oz. caulking cartridges.


    • Easily applied by brush or trowel
    • Forms a seamless, elastomeric membrane for above grade walls
    • Integral mold resistant formulation
    • Excellent adhesion to most construction surfaces such as exterior gypsum boards, CMU, concrete, stone, wood and metal
    • May be applied to damp concrete
    • Passes NFPA 285 Fire Test

    Coverage Calculator

    • 4-4 Gallons per 100sf**


    This is intended as a general guideline only, coverage can vary based on many factors.


    KARNAK 323 K-NRG Gap Seal FR is a liquid applied sealant used to construct high performance building envelope assemblies requiring an air & water barrier membrane.  Use to seal gaps around windows, doors, rough openings, changes in angles, transitions between dissimilar materials and joints in wall substrates.  When combined with KARNAK’s air barrier coatings and accessories,    323 K-NRG Gap Seal FR forms a complete wall air-barrier system.  Commonly used on a variety of wall substrates and sheathing prior to the installation of exterior cladding.

    Preparation & Application

    Surfaces should be clean and free of frost, oil, grease, dirt, excess mortar or other contaminants. All surfaces must be sound, dry (except damp concrete). New concrete should be cured for a minimum of 7 days before 323 K-NRG Gap Seal FR is applied.

    323 K-NRG Gap Seal FR may be applied by brush or trowel. Application should be free of voids when transitioning onto applied flashing membrane to create a uniform air-barrier. Regularly monitor wet mil thickness during application to assure adequate coverage.
    Joints between panels of exterior grade gypsum, plywood and rigid insulation up to 1/4” wide should be filled with a trowel application of 323 K-NRG Gap Seal prior to application of liquid membrane. Press material firmly with trowel or brush over the area to seal. Spread sealant to an average thickness of 1/16” (64 wet mils).

    Joints between 1/4” – 1/2” wide should be three-coursed with 323 K-NRG Gap Seal FR and reinforcement fabric. Spread sealant to an average thickness of 1/16”. Immediately embed reinforcing fabric into the wet material and smooth out. Apply another application over the fabric and feather onto surface. Reinforcing fabric should extend 3” beyond each side of the joint.

    Joints wider than 1/2” are not permitted. Steps should be taken to use an appropriate backer material to fill the joint first before three-coursing with 323 K-NRG Gap Seal FR and reinforcement fabric. Transition joints between two dissimilar materials such as at beams, columns, window and door frames, etc., should be three-coursed with 323 K-NRG Gap Seal and reinforcement fabric. Center fabric reinforcement so that it extends a minimum of 3” onto both substrates (Refer to local code for flashing requirements on the exterior wall assembly)

    323 K-NRG Gap Seal FR is not designed for permanent exposure. Product is designed to withstand job site exposure for up to 9 months, however, good construction practice calls for covering as soon as possible. Wherever possible, begin covering membrane on south exposures, followed by remainder of surface.

    Caution/Care of Tools

    PROTECT FROM FREEZING.  Product must be protected from damage during construction.  Do not apply to wet surfaces, except damp concrete.  Coating not designed for permanent exposure to weather.  Protect as soon as possible.  However, coating may be exposed up to 9 months, if necessary.

    K-NRG Gap Seal FR shall not be applied when ambient (air) and substrate temperatures are below 40°F (5°C).  The product should not be applied if it is raining, or rain is forecasted within 24 hours after application.  Product should not be applied if it is expected that the ambient temperature will fall below 32°F within 48 hours. Ensure newly coated CMU walls are protected at the roof line to prevent water infiltration into the wall cavity.

    Close container when not in use.  Avoid prolonged contact with skin.  Use proper protective equipment during application.  Avoid breathing of vapors as it may cause respiratory tract irritation. If swallowed, seek medical attention immediately.  In case of eye contact, open eyelids wide and flush immediately with plenty of water for at least 15 minutes.   Dispose of in an environmentally safe manner.  Cover air intakes during application and while drying.  Keep out of reach of children.  Protect from freezing.


    White material is still wet, tools may be cleaned with water.  Dry coating can be cleaned with 709 Karna-Klean or Xylene or similar solvent, taking the necessary precautions when handling flammable materials.

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