Lightweight concrete—specifically gypsum-based concrete—has become an essential material for radiant floor heating systems, soundproofing, and fire-resistive floor assemblies. Unlike traditional Portland cement concrete, gypsum concrete is self-leveling, dries faster, and provides superior thermal conductivity for radiant heating applications. However, finding, specifying, and installing this specialized material requires knowledge that goes beyond what most general contractors and homeowners possess.
What Is Gypsum Concrete?
Gypsum concrete is a flowable, self-leveling material made from calcined gypsum (calcium sulfate hemihydrate) mixed with sand and water. Unlike conventional concrete, which uses Portland cement as the binder, gypsum concrete relies on the natural setting properties of gypsum—a mineral that has been used in construction for thousands of years, dating back to the ancient Egyptians.
The resulting material has several distinct advantages for certain applications:
- Self-leveling: Gypsum concrete flows easily and seeks its own level, eliminating the need for extensive screeding
- Thermal conductivity: Excellent heat transfer properties make it ideal for radiant floor heating systems
- Fire resistance: Gypsum is naturally fire-resistant, providing up to 2-hour fire ratings in many assemblies
- Sound dampening: Higher density than lightweight aggregate concrete improves acoustic performance
- Fast drying: Typically ready for floor covering in 24-48 hours, compared to 28 days for traditional concrete
Major Manufacturers and Products
Two major manufacturers dominate the gypsum concrete market in North America:
| Manufacturer | Product Name | Bag Size | Compressive Strength | Typical Coverage (per bag at 1.5 in) |
|---|---|---|---|---|
| Maxxon Corporation | Gyp-Crete Thermafloor | 50 lbs | 1,200-2,500 psi | ~2.5 sq. ft. |
| Hacker Industries | Gyp-Span | 80 lbs | 1,800-3,200 psi | ~4 sq. ft. |
Maxxon Corporation (Hamel, Minnesota) produces Gyp-Crete Thermafloor, the most widely specified gypsum concrete for radiant heating. Hacker Industries (Newport Beach, California) manufactures Gyp-Span, a comparable product with slightly higher compressive strength ratings. Both products require licensed applicators for installation—these are exclusive dealers who have been trained and certified to pump and finish the material.
Licensed Applicators: Why They Are Required
Gypsum concrete is not available at home centers or through standard concrete ready-mix suppliers. It must be ordered through licensed applicators certified by the manufacturer. There are three reasons for this:
- Specialized equipment: Gypsum concrete is a thin, flowable material that requires specialized pumping equipment to place. Standard concrete pumps cannot handle the material.
- Quality control: The water-to-powder ratio must be precisely controlled. Too much water reduces strength; too little prevents proper flow. Licensed applicators have calibrated mixing equipment.
- Warranty: Manufacturers typically only warranty the product when installed by their certified network. Unauthorized installation voids the warranty and may create liability issues.
Can You Mix It Yourself?
For small pours—such as a bathroom remodel or a small addition—both Gyp-Crete Thermafloor (50-lb bags) and Gyp-Span (80-lb bags) are available for self-mixing. However, the logistics are challenging. A 1.5-inch thick slab requires approximately 11 pounds of material per square foot. For a 200-square-foot room, that is 2,200 pounds of material—44 bags of Gyp-Crete or 28 bags of Gyp-Span—plus the sand and water.
Mixing this volume by hand or even with a standard mortar mixer produces inconsistent results. The material must be mixed to a precise, cream-like consistency that flows freely but does not separate. For all but the smallest applications, hiring a licensed applicator with a truck-mounted mixing and pumping system is the practical choice.
Design Considerations for Radiant Slabs
When designing a gypsum concrete radiant slab over wood framing, several factors must be addressed:
- Minimum thickness: Gypsum concrete should be at least 1.5 inches thick over the highest point of the radiant tubing to prevent cracking
- Reinforcement: Welded wire mesh or polypropylene fibers are typically added for crack control
- Expansion joints: Control joints must be placed at doorways and in rooms exceeding 30 feet in any dimension
- Curing: While gypsum concrete dries quickly, it should not be subjected to foot traffic for at least 24 hours or heavy loads for 3-4 days
- Floor covering: Most floor coverings (tile, hardwood, carpet, LVP) can be installed over cured gypsum concrete with appropriate primers
Cost Comparison: Gypsum vs. Traditional Concrete
| Cost Factor | Gypsum Concrete | Traditional Lightweight Concrete |
|---|---|---|
| Material cost per sq. ft. (1.5 in) | $2.50-4.00 | $1.80-3.00 |
| Installation labor | $1.50-2.50 (pump required) | $2.00-4.00 (screeding required) |
| Drying time to floor covering | 24-48 hours | 28 days minimum |
| Project schedule impact | Minimal delay | 4-6 week delay |
| Thermal conductivity (Btu/h·ft·°F) | ~0.35 | ~0.50 (standard concrete) |
Finding a Licensed Applicator
To find licensed applicators in your area, contact the manufacturers directly:
- Maxxon Corporation: (800) 356-7887 or www.maxxon.com
- Hacker Industries: (800) 642-3455 or www.hackerindustries.com
You can also check the Yellow Pages under “Concrete Contractors” and ask specifically for applicators certified for gypsum concrete underfloor systems. Many concrete contractors have relationships with the licensed applicators and can subcontract the pour.
For more on concrete materials and floor systems, see our guide on autoclaved aerated concrete and comparison of flooring types.