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
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Multi-Family Application / MarketApartments, condominiums, hotels, motels, dorms, commercial buildings and commercial renovation projects. |
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

Product Resources
Technical Data |
Properties |
ASTM |
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, E136 |
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 |