Nelson Firestop CLK™ Sealant

Protect From the Dangers of Fire, Smoke, Gases and Water

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What's special about this sealant?

  • Versatile, ready to use, one component silicone sealant for a plethora of applications
  • Highly adhesive and easy to apply, this non-shrinking and non-toxic caulking maintains its flexibility and allows for movement or vibration, retaining sealing qualities even with expansion, contraction, or any other fluctuations
  • Waterproof, smoke proof, and gas proof – so nothing gets through
  • Requires no cable derating, and is easily repenetrated
  • Click for More Features



NFS-AA529 Nelson CLK™ Silicone Sealant Non-Sag – 10.3 oz Tube 18.5 in3 (304ml) 14.6 oz
NFS-AA492 Nelson CLK™ Silicone Sealant Non-Sag - 5 Gallon Pail 1,155 in3 (19.0 L) 60 lbs

  • The non-sag, quick drying application won’t run, and is suitable for overhead applications; no damming required
  • The self-leveling  liquid for quick flow and fill in has excellent viscosity
  • Up to 4 hour rating for added safety
  • Elastomeric (Flexible Cure) makes it easy to work with in many applications
  • Acoustically tested for excellent noise reduction properties
  • Can be used for non-combustible pipe throughstop penetrations, and for floor-to-wall, floor-to-floor and head of wall applications
  • 1 year manufacturer’s warranty


This flexible sealant is used to protect and prevent the spread of fire, smoke, gases and water. This product is ideal for applications like through firestop penetrations and construction joints, because it is used for simple penetrations like those around metallic pipes or conduits.

Designed with fire rating protection in mind, it is flexible enough to withstand the shifts that can occur in joints.
No maintenance is required; in the future, if you need to change the sealant, simply cut through the existing seal and with a knife and reseal the opening with more Nelson CLK™.


It is offered in two forms:

The non-sag caulk can be troweled while the self-leveling grade is better suited for floor applications. The non-sag can be applied using a conventional caulk gun, bulk loader or by trowel. For larger applications it can be pumped directly from the pail.
The self leveling formula fluid can be poured into place in floor applications. Apply the required depth of sealant beginning at the edge of the opening and ensure that the sealant makes complete contact with the inside surface of the opening, as well as the surface of the penetrating item.





Physical Properties
Color Brick Red
Weight 10.75 lbs./ gal.
Consistency Thixotropic
Application Temp 40° F (4° C) to 90° F (32° C)
Service Temp 0° F (-18° C) to 110° F (43° C)
Cure Time Less than 2 weeks for 1/2" thickness
Hazardous Ingredients None
STC Rating 52
Test Compliance
  • Non-Sag
    Flame spread………….…… 5
    Smoke developed………… 40
  • Self-Leveling
    Flame spread………….……5
    Smoke developed………….35
ASTM E90 Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements
ASTM E84 and UL 1479 Test method for through stop fire penetrations.
ASTM E-1966 andUL 2079 Test method for fire resistance of building joint systems.
Testing Data
For specific test criteria, refer to the UL Fire Resistance Directory.
Storage & Handling
Nelson CLK™ should be stored at temperatures between 40°F (4°C) and 90°F (32°C).
Protect from feezing.
Expected shelf life is one year from date of shipment.


Non Sag
Extrusion Rate (60 sec. @ 40 psi) 80-125
Slump (inches) 0.125"
Specific Gravity (WPG * 0.1202) 1.19-1.29
Extrusion Rate (gm/min.) 100-500
Skin Over Time (min.) less than 15 min
Tack Free Time (min.) less than 60 min
Cure Time less than 2 weeks for 1/2" thickness
Shore “A” Durometer 17-25
Tensile (psi) 200-260
Elongation (%) 600-800
Modulus (psi) 70-75
Flame Spread (ASTM E84) 5
Smoke Developed (ASTM E84) 40
STC Rating (ASTM E90) 52
Self Level
Viscosity 44,000-66,000 cps
Specific Gravity (WPG * 0.1202) 1.23-1.32
Skin Over Time (min.) less than 20 min
Tack Free Time (min.) less than 220 min
Cure Time less than 2 weeks for 1/2" thickness
Shore “A” Durometer 15-25
Tensile (psi) 120-220
Elongation (%) 300-700
Modulus (psi) 35-65
Flame Spread (ASTM E84) 5
Smoke Developed (ASTM E84) 35
STC Rating (ASTM E90) 52







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