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At a Glance
Why Choose This Product
Helps limit stress transfer between the substrate and finished tile
Meets ANSI A118.10 waterproofing requirements
Meets ANSI A118.12 requirements for crack isolation
Raised cavities help compensate for moisture vapor pressure
Helps distribute loads across the tile assembly
Helps distribute heat across the finished tile installation
Independently tested over concrete, plywood, and OSB
Earned Heavy or Extra Heavy ASTM C627 ratings in tested assemblies
Product Information
GURU® G-FLEX Uncoupling Membrane is a 1/8" waterproof tile underlayment that helps protect ceramic, porcelain, and natural stone installations from substrate movement and moisture. Its HDPE waterproof sheet and thermo-bonded polypropylene fiber backing create a durable layer beneath tile while supporting reliable mortar bonding.
G-FLEX allows the tile covering and substrate to move independently, helping reduce stress that can contribute to cracked tile. It meets ANSI A118.12 requirements as a crack isolation membrane and ANSI A118.10 requirements as a waterproofing membrane, combining two important protective functions in one tile underlayment.
The raised cavity design provides space for vapor pressure compensation while distributing loads and heat across the tile assembly. Depending on the complete assembly, independent ASTM C627 testing produced Heavy or Extra Heavy service ratings, giving residential and commercial projects a proven foundation for long-term tile performance.
G-FLEX is designed for interior and exterior tile installations over suitable substrates. It has been independently tested over concrete, plywood, and OSB assemblies. Its combination of waterproofing, uncoupling, and load performance makes it suitable for residential floors and demanding commercial spaces such as kitchens, food plants, breweries, dairies, and airports.
Product Resources
Common Questions
GURU G-FLEX is installed beneath ceramic, porcelain, and natural stone tile to provide uncoupling, waterproofing, crack isolation, vapor pressure compensation, and load distribution. It allows the tile covering and supporting substrate to move independently, helping reduce stress transfer and improve the performance of the completed tile assembly.
Yes. G-FLEX meets ANSI A118.10 waterproofing requirements, and its HDPE sheet provides the waterproof layer. To create a continuous waterproof assembly, seams, edges, penetrations, and transitions must be treated according to GURU instructions so moisture cannot travel around or between individual membrane sections.
G-FLEX helps reduce the risk of stress-related tile cracking, but it cannot eliminate every possible cause of failure. As a crack isolation membrane, it limits stress transfer from substrate movement and meets ANSI A118.12 requirements. The supporting floor must still be structurally sound and meet applicable tile industry requirements.
G-FLEX has been independently tested in tile assemblies over concrete slabs, plywood, and OSB subfloors. Performance depends on the entire floor assembly, including subfloor thickness, joist spacing, tile size, mortar, and installation method. Confirm that the supporting surface and framing meet current GURU and tile industry requirements.
G-FLEX is designed for use beneath ceramic, porcelain, and natural stone tile. Tile size, thickness, mortar selection, and required coverage depend on the complete floor assembly and project conditions. Follow current GURU instructions along with the tile and mortar manufacturer requirements when selecting materials for the installation.
Yes. The G-FLEX technical data sheet identifies the membrane for indoor and outdoor tile installations over suitable substrates. It is designed for residential and commercial applications, including demanding environments where waterproofing, crack isolation, vapor management, and load distribution are needed beneath the finished tile covering.
The GURU technical data sheet specifies modified thin-set mortar meeting ANSI A118.11 and A118.15 for bonding G-FLEX to the substrate and setting tile over the membrane. Tested assemblies used a 1/4" × 1/4" square-notched trowel. Always follow current GURU and mortar manufacturer instructions for the specific project.
G-FLEX has an overall thickness of 1/8" (3 mm). It consists of a waterproof HDPE sheet with raised cavities and a non-woven backing made from thermo-bonded polypropylene fibers. Mortar and tile add to the final floor height, so completed assembly thickness varies by tile, mortar, and installation method.
