TECH TALK ––––––––––––––––––––––––––––––––––––––––––––––––––––––––– unskilled tile installations and other construction trades’ workforce. If surfaces are not true and straight, then extra adhesive is required to pack the finished work out to its proper alignment. Preparation trades who fail to provide good surfaces – or tilers who have poor mortar screeding skills – end up using thicker adhesive layers. Increased use of screed isolation layers/ membranes and uncoupling mats For a number of reasons, includ- ing efforts to prevent efflores- cence staining, there has been an increase in the application of waterproofing membranes over the top of mortar screeds. Often the aim is to prevent water enter- ing the mortar screed and leach- ing calcium stains out. Such a waterproof membrane prevents moisture in the tile adhesive from being absorbed into the screed, thereby delaying curing and dry- ing of the adhesive. The increased use of other dense layers over the screed, such as uncoupling, or crack-isolation membranes made of bitumen or plastics such as polyethylene, have a similar effect of preventing the absorption of water in the tile adhesive into the screed. Delayed curing and drying of latex/polymer modified adhesives All of the above changes result in slower curing and drying of the tile adhesive. For internal tiling, this is not a great issue. It means wall installations need to have supports left in place longer to reduce creep, until a proper cure has occurred, and floors should not be trafficked for a number of days, instead of the usual 24 hours. But when it comes to exter- nal tiling, this slow curing and drying can be a major problem. This delay in curing is specifi- cally referred to in the TCNA Handbook, which at least since 2011 has stated under the heading Latex/polymer modified Portland Cement Mortar: “When installing 8” x 8” or larger impervious tiles over a waterproof or crack isolation membrane, or other impervious substrate, longer curing times will be required. A rapid setting latex/polymer mod- ified cement mortar may need to be specified for faster curing. Because latexes vary considerably, the directions of the latex/polymer mortar manufacturer must be fol- lowed explicitly.” Despite this call for the man- ufacturer’s directions to be fol- lowed explicitly, a review of a large number of adhesive product data sheets revealed no mention of delayed curing when dense tiles and the adhesive were used over impervious substrates. The most ominous warning also comes from the TCNA Handbook, which states: “When latex/polymer modified 84 TileLetter | 2018