Not on your life! But you’d never know it by the way most profes- sionals view this issue. The TCNA Handbook and ANSI A108 strong- ly recommend that 80% coverage should be attained for most instal- lation scenarios, and rightfully so (exterior projects and showers rec- ommend a minimum 95% cover- age). The Handbook even goes so far as to offer explicit instructions as to how this can be obtained (thanks to Joe Tarver’s research years ago at the NTCA). I agree wholeheartedly that the 80% goal should be reached on every tile installation; but I dis- agree that if it is not attained it will doom an installation to failure. I have seen too many installations that have been in for two years, three years and more that have never had the slightest inkling of failure until dramatic structural movement triggered lateral stress – most times as a crack in the concrete slab – that caused tile to dis-bond and shear loose. Then, if the coverage was something less than 80%, the tile contractor got blamed for the entire failure, or at least the vast majority of it. Never mind that the floor never failed for several years. Never mind that it is obvious that a crack in the con- crete triggered the stress put on the mortar. It becomes the fault of the tile contractor because of the less- than-80%-coverage issue. I disagree! I’m 100% on the side of the tile contractor here! Let me shed some needed light on this topic. Let's go back to the 1950s and 60s when thin-set mortars were first being introduced to the market. ANSI was tasked with evaluating these new mortars that were begin- ning to replace full-blown mud- bed installations. ANSI A118.1 was developed, which included a porcelain tile shear strength rating of 150 psi. ANSI A118.4 came in at a porcelain shear of 200 psi. Does lack of 80% mortar coverage mean that a tile installation will fail? Sponsored by TECH TALK –––––––––––––––––––––––––––– By Tom D. Lynch, CSI 44 TileLetter | February 2018