GSL® M3.4 premium gypsum cement is an exciting, unique product for creating a self-leveling underlayment for use over virtually all interior surfaces.

Pumpable, GSL® delivers high strength, good water resistance and outstanding adhesion. Applications from nearly a featheredge up to 3” depth can be achieved in a single pour. GSL® remains flowable for nearly 30 minutes, yet will withstand foot traffic at any depth in about two hours. This product offers high density, yet less finished weight and more exibility than portland cement self-levelers.

Unlike portland cement, gypsum does not shrink and requires no hand finishing tools other than a darby that establishes thickness and uniformity. Typically installed with a specialty mixing machine capable of placing 20,000 to 30,000 square feet per day. GSL® M3.4 is specially formulated to add mass to a floor ceiling assembly and help control airborne noise.

GSL® is UL approved on all standard assemblies providing developers the fire safety assurance required in today’s multi-family projects.

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
  • Provides additional sound control enhancements as tested under ASTM E90, Airborne Noise or STC and ASTM E492, Impact Noise or IIC
  • Covers virtually any surface (especially plywood and OSB subfloors)
  • Durable High Strength Gypsum
  • Excellent for floor leveling in deep fill applications
  • Outstanding heal that provides a smooth, dense surface
  • Open time up to 30 minutes
  • Non-Alkaline—adhesive friendly
  • Can pour up to 3″ in single lift
  • Withstands construction but should be protected when exposed to trade traffic or wheeled loads
  • As little as 3/8” coverage over other surfaces


  • Multi-family
  • Renovations
  • Floor leveling
  • Light commercial
  • Commercial/retail/office
  • Hotel/motel
  • Assisted living/senior care
  • For sound and fire control applications

GSL® M3.4

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


• Building must be fully enclosed including windows and roof.
• Temperature must be 45ºF and rising and maintain “a minimum of” 45ºF temperature for a minimum of 4 to 5 days after installation.
• Subfloor must be a minimum of L/360 and broom swept with all excess wall board mud removed, all holes patched.
• Wood construction must be with tongue and groove subfloor (OSB or plywood).
• Adequate drying must be maintained until the moisture in the gypsum has been allowed to evaporate. This requirement is typically a minimum of 5 to 7 days but   may be longer depending on humidity conditions in the local environment.
• For installation on concrete substrates the subfloor must be fully cured (typically 28 days). Moisture tests should be performed to assure proper hydration under ASTM F1869 to assure MVE level is less than 3.0 lb. per 1000 square feet.
• For below grade applications or over crawl space in residential, vapor barriers must be applied.


Subfloor must be properly primed. Use GSL PRIMER on all surfaces. Approved priming methods include: roller, soft bristle broom, brush or spray. All supporting surfaces shall be structurally sound, solid, free of movement and well bonded. They shall be free of dust, oil, grease, tar or other contaminants that may act as a bond breaker. Deflection cannot exceed L/360.


Before GSL PRIMER application, dilute 1 part GSL PRIMER concentrate to 4 parts potable water (1:4). Using a long handle roller, soft bristle broom, brush or sprayer, apply GSL PRIMER at a coverage rate of 270-320 sq. ft. per gallon of primer solution. Coverage rate varies depending upon surface porosity. Ensure a complete and uniform coverage. Allow to become very tacky or dry (about 1 hour).


Follow DEPENDABLE, LLC guidelines and use only with trained installers of GSL.

Strength Ratio

3200 – 4000 psi


Plywood, OSB, concrete and approved acoustical treatment are acceptable. Wood material must be of proper thickness, tongue and groove construction and properly fastened. Concrete should be clean, dry and free of obvious structural problems. All substrates must be properly sealed and primed before the GSL floor underlayment is applied.


Material should be kept in a dry area. Avoid ambient temperature below 40° F and above 110° F for prolonged periods. Shelf-life of six months.


 Multiple lifts: Multiple lifts does not require a primer with GSL. Second lift can be accomplished upon an initial set that can handle the load of the hose operator and finisher.

NOTE: Temperature and humidity levels affect the drying characteristics of GSL. However, unlike Portland cement materials, GSL may be force dried with the use of heat or fans once set.


• GSL is NOT a wear surface.
• DO NOT INSTALL WITHOUT TONGUE AND GROOVE SUBFLOOR unless utilizing back bracing or filling all joints.
• CHECK JOIST DEFLECTION and assure performance greater than L/360
• ASSURE BUILDING IS COMPLETELY INCLOSED including doors, windows and roof.
• PROVIDE VENTILATION after placement of GSL.


• Where hydrostatic pressure (water) is present or moisture emissions exceeds level permitted for installed floor covering.
• Where surface or ambient temperature falls to or below 45°F 72 hours before or after installation.
• As a trowelled patch or at less than natural minimum flow thickness.
• Exterior, exposed applications or as a wear surface.