FIRM-FILL® Gypsum Concrete

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 105 UL listings, FIRM-FILL® Gypsum Concrete floor underlayment is an excellent choice for jobs needing compressive strengths up to 2200 psi.


Recommended For


Features & Benefits

  • Flattens subfloors
  • Provides excellent STC (sound transmission) and IIC (impact isolation) ratings
  • Possesses over 105 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


External Resources

Sweets ProductTAG
CAD Details


Product Resources

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

Featured Application

Margaritaville Vacation Club, U.S. Virgin Islands
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 - 2250 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