FIRM-FILL® Gypsum Concrete

The original FIRM-FILL® Gypsum Concrete floor underlayment is designed for use in multi-family housing to satisfy acoustical ratings and fire codes. With excellent STC and IIC ratings as well as over 100 UL listings, FIRM-FILL® Gypsum Concrete floor underlayment is an excellent choice for jobs needing compressive strengths up to 2000 psi.


Recommended For


Features & Benefits

  • Flattens subfloors
  • Provides excellent STC (sound transmission) and IIC (impact isolation) ratings
  • Possesses over 100 UL listings
  • Lightweight and crack resistant
  • Easily installed; over 25,000 square feet can be installed per day
  • Quick drying; can be walked on in 90 minutes
  • Expert application; installed only by trained, Licensed Applicators
  • Approvals from ICC-ES and HUD
  • Meets ASTM F2419, Standard Practice for the Installation of Thick Poured Gypsum Concrete Underlayments and the Preparation of the Surface to Receive Resilient Flooring


FIRM-FILL<span>®</span> Gypsum Concrete

Product Resources

Key: Word PDF Web Page
Product Submittal
3-Part Specifications
Project References
Drying Conditions Flyer
Guidelines for Finished Floor Coverings

Featured Application

Historic Eaton Block and Eaton Hotel, KS
Wilderness on the Lake, WI


Technical Data
Weight 7 lbs/ft2 at 3/4" (19 mm) C472M
Thickness 3/4" (19mm) (minimum over wood) to 3 1/2" (89mm)  
Compressive Strength 1200 - 2000 psi C472M
Thermal Performance K-value of 2.45 Btu/ft2·h·°F; R-value of 0.41 ft2·h·°F/Btu C177
Fire Hazard Classification Flamespread index 0; Fuel Contribution 0; Smoke Density 0 E84,
Patty Size 8" (203mm) plus or minus 1/2" (13mm) in diameter  
Sand 1/8" (3mm) or less washed plaster or masonry sand E11
UL listings Listed in over 100 1, 2, 3 and 4 hour floor/ceiling assemblies