GSL® RH radiant heat underlayment is a fast, quick-setting gypsum cement formulated for radiant floor heating applications.

GSL® RH provides compressive strengths up to 3500 psi. Consult your trained contractor from DEPENDABLE, LLC on how to achieve the compressive strength needed on your next project.

GSL® is designed for installation by trained contractors from DEPENDABLE, LLC.  Please consult with a local representative for a list of contractors in a specific geography.

  • Provides additional protection for fire resistance as shown in UL approved assemblies
  • Non-Combustible
  • Provides additional sound control enhancements as tested under ASTM E90, Airborne Noise or STC and ASTM E492, Impact Noise or IIC
  • Provides an ultimate radiant mass with an even transfer of heat
  • For radiant floor heating systems
  • Can be poured over hot water tubes, electric heating cables or mats
  • Smooth and formulated to resist breakdown
  • Eliminates noisy floors and nail pops
  • Reduces air leaks and baseboards drafts


  • Multi-family
  • Light commercial
  • Commercial/retail/office
  • Hotel/motel
  • For sound and fire control applications


  • 80 lb. (36 kg.) Bag, valve double wall bag

The building must be fully enclosed, and a minimum temperature of 50 ̊F must be maintained during the installation and for a period of 14 to 21 days (typical drying period for a 1 to 1/2” application) after the installation of GSL RH.

The subfloor must be fine broom cleaned and free of all contaminants. Prior to pouring GSL RH,an priming system must be used.

Adequate ventilation must be provided for a period of 14 to 21 days after installation of the underlayment to ensure drying of the underlayment. For thicker applications, a longer drying time may be necessary. The structural subfloor should be adequate to withstand designed loads with a minimum deflection criteria of L/360.

Installations over concrete slabs require the concrete to be properly cured (typically 28 days) prior installation of the GSL RH.

For any glue down floor covering, including vinyl or resilient flooring, apply an approved GSL surface sealer prior to the installation of the floor goods.


• No single application of GSL RH Floor Underlayment should exceed 3” in depth. Consult DEPENDABLE, LLC contractors on how to achieve depths greater than 3”.
• Any material poured above a crawl space must be protected by a vapor  barrier.
• After installation of the GSL RH and prior to the resumption of construction, place temporary wood planking over underlayment where heavy wheeled or concrete loads will occur.
• GSL RH is not designed to be installed on or below grade, except over well-drained structural substrates.
• The structural floor should be designed to withstand designed loads with a minimum deflection criteria of L/360.
• Unless otherwise stated, GSL RH should not be used as a wearing surface.
• Unless otherwise stated, GSL RH should not be used for exterior applications or where they will come in prolonged contact with water.
• GSL is approved for use over concrete and new plywood or OSB. Other substrates and conditions may require special preparation. Consult the manufacturer before installation over other types of substrates.
• GSL RH is only one component of an effective floor-ceiling fire rated and sound rated assembly. Care must be taken in the installation of all construction components to assure the ultimate in design performance.