Schluter DITRA Over WBI Radiant Panels

WBI has worked with Schluter to evaluate DITRA over its radiant panels, providing another underlayment option for tile projects. When installing Schluter products over WBI panels, follow Schluter’s current installation instructions and technical guidance for the specific panel, membrane, and tile assembly.

Tested for residential applications

Schluter reported successful shear bond testing with both traditional mortar-bonded DITRA and DITRA Peel & Stick over WBI panel samples.

A complete RadiantBoard assembly using PRIMER-PS, DITRA Peel & Stick, and 12-by-12-inch porcelain tile installed with ALL-SET achieved a Residential rating in Robinson Floor Testing. That test used panels glued and screwed to an OSB subfloor, with PEX installed in every groove.

Traditional DITRA installation

The general installation sequence is:

WBI radiant panel and PEX → Schluter PRIMER-U → Schluter ALL-SET thinset → DITRA → ALL-SET thinset → tile and grout.

Apply and dry PRIMER-U, embed DITRA into fresh thinset, and install the tile according to Schluter’s instructions. Follow Schluter’s guidance for surface preparation, bonding materials, mortar coverage, curing, movement joints, waterproofing, and treatment of tubing grooves. Confirm any assembly details not addressed in the published instructions with Schluter Technical Services before proceeding.

DITRA Peel & Stick

DITRA Peel & Stick uses an adhesive backing to attach the membrane to the prepared panel surface. Follow Schluter’s guidance for substrate preparation, primer selection, and membrane installation. Thinset mortar is still required above the membrane to install the tile.

Cement backer board remains an option

Cement backer board, including products such as HardieBacker, can still be used in an appropriate tile assembly over WBI panels. Follow WBI’s panel requirements and the backer board manufacturer’s instructions for bedding mortar, fastening, and joint treatment. Locate fasteners carefully to avoid the PEX tubing.

Where waterproofing is required, install a compatible system according to its manufacturer’s instructions. Cement backer board alone does not make the assembly waterproof.

Contact WBI for panel information and Schluter Technical Services for guidance on installing Schluter products over your specific assembly.

About The Author

Patrick Gourley

Operations Manager, WBI

Patrick brings more than 20 years of experience in construction and fabrication to his role as Operations Manager at Warm Brothers Inc. (WBI). With a career rooted in hands-on building, manufacturing, and problem-solving, Patrick oversees WBI’s day-to-day operations, including panel… Read More