Use this 3 part SimpleSpecs™ master specification to specify poured-in-place, self-leveling gypsum cement underlayment.
Gypsum-based floor underlayments are self-leveling products used for filling and leveling floors. They must be placed over a concrete or plywood structural floor; they do not provide structure on their own. They are not suitable for exterior use and must be covered with finished flooring.
Underlayments may be used in conjunction with radiant floor heating systems and sound mat or sound board for improved STC and IIC ratings.
Gypsum concrete is lightweight. A 1.5-inch slab of gypsum concrete weighs 13 pounds per square foot versus 18 pounds per square foot for regular concrete. Even though gypsum concrete weighs less, it still has the same compressive strength as regular concrete, based on its application as underlayment or top coat flooring.
Gypsum is fire-resistant and the assemblies are UL listed.
Check with the underlayment manufacturer to select a product to meet your project requirements.
To learn more about gypsum concrete, visit Wikipedia.