What is Gypsum Concrete?

Gypsum concrete is a mixture of gypsum plaster, portland cement, and sand that is pumped and poured over floor substrates to create a smooth, level surface. It is primarily used as an underlayment in multi-story buildings where fire ratings and sound attenuation between floors are critical requirements.

Why Gypsum Concrete Matters in Multi-Family Projects

Building codes for apartments, condominiums, and hotels require specific fire ratings and sound transmission ratings between dwelling units. Gypsum concrete plays a key role in meeting these requirements.

• Fire Protection — Gypsum concrete is non-combustible and provides excellent fire ratings for floor-ceiling assemblies. It is a key component in many UL-listed fire-rated designs.
• Sound Control — A properly installed gypsum concrete underlayment significantly improves both STC (Sound Transmission Class) and IIC (Impact Insulation Class) ratings, reducing noise complaints between floors.
• Floor Leveling — Gypsum concrete is self-leveling, creating a perfectly flat surface for finished flooring materials like hardwood, tile, luxury vinyl, and carpet.
• Lightweight — At roughly half the weight of traditional concrete, gypsum concrete reduces the structural load on buildings, potentially allowing for lighter framing systems.

Installation Process

Professional gypsum concrete installation involves several steps: substrate preparation, installation of sound mat or isolation membrane, placement of lath or reinforcement, and pumping of the gypsum concrete mixture. The material typically cures to walkable hardness within 90 minutes to 2 hours, and is ready for flooring installation within days rather than the weeks required for traditional concrete.

Common Mistakes to Avoid

• Insufficient substrate preparation leading to poor adhesion
• Incorrect thickness that fails to meet fire rating requirements
• Exposure to water or moisture before and after installation
• Premature installation of finished flooring before adequate curing

At EM Building Contractors, LLC, our gypsum concrete crews are trained and certified to deliver consistent, code-compliant installations on every project. We work closely with engineers and architects to ensure every pour meets the specified fire and acoustical ratings.