This release of moisture can affect the curing of the mortar and the grout. Many crack-isolation/ waterproofing membranes – spe- cifically those membranes that are flat – have limited resistance to pressure from moisture since there is nowhere for the moisture to be released. This in turn creates pres- sure that can cause the membrane to bubble or debond from the con- crete slab. The TCNA Handbook declares that an uncoupling mem- brane must have free space or empty cavities on the underside of the membrane that inherently allow for moisture/vapor release and eventually equalization. The TCNA Handbook prologue uncoupling definition was updated again in 2014 to include: “The uncoupling membrane must achieve 50 PSI or greater shear bond strength in 7 days per the test method in ANSI A118.12 Section 5.1.3.” This addition was in response to the concerns conveyed by labor and some forensic consultants that there were certain so-called “uncoupling membranes” that were failing to the extent of sev- eral millions of dollars for repair and damages. The main mode of failure was traced to the bond between the substrate (majority plywood) and the underside of the membrane where the fleece/mesh or other had delaminated. Until an ANSI standard is created for uncoupling, this requirement is a reasonable stop-gap to identify those membranes that are not per- forming. The look of uncoupling has changed over the years but the basic criterion has remained the same: a configured membrane with open-air space to allow for independent movement between the tile and the substrate. Some of the newest additions to the uncou- pling category now incorporate a floor warming system and have an optional integrated sound control and thermal break (for quicker heating reaction time). The need for a standard The need for an ANSI standard has become more essential in North America than ever before, with the proliferation of new uncoupling membranes that have emerged in the market recently. The good news is that the Materials and Methods Standards Association (MMSA) has had a subcommittee that has been working on developing a F128 TECH TALK –––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 94 TileLetter | July 2019