Gypsum Floor Underlayments are non-structural, poured gypsum concrete floor underlayments that supply fire resistance and sound control while providing a durable, flat surface for finished floor coverings. The following procedures are required to a successful finished floor installation.

Installation

When working with gypsum floor underlayments, be sure to wear personal protective equipment. Avoid dust inhalation. Many gypsum floor underlayments contain crystalline silica, a known

occupational carcinogen.

Before, during, and after installation of a gypsum floor underlayments, building interior shall be enclosed and maintained at a temperature above 50°F until structure and subfloor temperatures are stabilized. Provide continuous ventilation and adequate heat to remove moisture rapidly from the area until the underlayment is dry. Provide mechanical ventilation if necessary.

Confirm the subfloor is structurally sound and conditions are suitable for installation of a gypsum floor underlayment. Design must be able to withstand design loads with a deflection limitation of L/360.

DRYING CONDITIONS

The drying time for gypsum floor underlayments is dependent upon several variables. Ventilation,

weather, humidity, the amount of water in the building and the underlayment at the time of installation, and the thickness of the underlayment will all affect the drying time of the gypsum floor underlayment.

Before, during and after installation of gypsum floor underlayments, the building interior must be properly ventilated and heated (minimum 50°F). Under these optimum conditions, a gypsum

concrete floor installed at 3/4″ thick should usually dry in about 7-10 days. In a building without all of these conditions present, the drying time can increase. Low temperatures, certain sands, poor ventilation and high humidity can lengthen the drying time.

Weather permitting; windows should be kept open until the gypsum floor underlayment is completely dry.

If not, mechanical ventilation and heat is necessary. Regardless of temperature, and/or weather conditions, the air must be exchanged daily in all areas until the gypsum floor underlayment is completely dry.

Do not install floor coverings until the gypsum floor underlayment is completely dry. The recommended procedure to test for dryness is to use a moisture meter with a gypsum scale.

Three recommended moisture meters:

The ASTM F1869 Calcium Chloride Test Method is not recommended. Surface Prep

Porosity of the gypsum floor underlayment is a major factor in the drying rate of adhesives. This porosity factor will greatly reduce the open time of the flooring adhesive. The application of Top

Coat/Sealer prior to the installation of the glue-down flooring will minimize the porosity of the gypsum floor underlayment. This step should be done by the company applying the gypsum underlayment, but usually is not. Before applying the Top Coat/Sealer, the flooring installer must test the underlayment for dryness; it must be fully dry.

The surface to receive the Top Coat/Sealer must be free of mud, oil, grease, and other contaminants. For best results, the Top Coat/Sealer should be applied about 1-2 hours prior to applying the adhesive. Make sure the surface is completely dry so adhesives can achieve maximum bond. Perform a bond test to ensure you have adequate bonding to the gypsum underlayment.

Armstrong S-185 Latex Primer and Mapei Primer L may be used as a Top Coat/Sealer for gypsum underlayments.

Some construction materials contain organic materials and must be installed properly to help avoid fungus or mold growth. To avoid growth of mold on construction materials such as wallboard, it is vital to maintain a low relative humidity both before and after placement of the gypsum floor underlayments. Proper ventilation is critical.