The documented prefill allowance has a waterproofing limitation.
ARDEX’s December 13, 2016 technical update permits ARDEX Liquid BackerBoard as a topside prefill over approved uncoupling membranes. Its attached approved list includes Schluter Ditra, Ditra Heat and Ditra XL, plus Progress Profiles Prodesso and Prodesso Heat.
The update excludes applications where the uncoupling membrane is being used for waterproofing. It also states that the membrane is not primed before this prefill. These instructions are specific to the named product and assembly; they do not authorize any self-leveling compound over any membrane.
ARDEX’s current product page still describes prefill over approved uncoupling membranes and encapsulation of electric floor heat. Follow the current product instructions, the exact membrane/heating instructions and required thickness, curing and substrate conditions before installation. The historical approval list alone does not expand a manufacturer’s current warranty.
Sources: attached ARDEX technical update 94 and approved-membrane list, and current ARDEX Liquid BackerBoard product guidance.
