the curing process. The membrane manufacturer would have to be con- tacted to verify and support this for use of their product. Installing on a slab with excessive internal moisture can be problemat- ic. Installing on a green slab presents the potential for additional unknown factors. Many factors come into play when considering relative humidity (RH) in a slab. In a new slab, curling of the top surface (especially at control joints) may occur causing the slab to exceed variations in flatness toler- ance for a tile installation. As a green slab cures (and curls), debonding or cracking of the tile bonded to it may also occur. Your 2018/2019 NTCA Reference Manual includes an excel- lent discussion on Ceramic Tile & Stone Installations over Concrete Substrates on pages 50 - 61. The troubleshooting guide on page 54 includes a discussion of identifying problems/causes/cures for excessive internal moisture in a concrete slab. It also references the test procedures for determining safe levels for mois- ture in a cured slab. In addition to consulting the NTCA Reference Manual and membrane manufacturer, it is important to involve your setting-material manu- facturer in the discussion for select- ing the correct bonding and grouting products to adhere to and properly handle the moisture emanating from the slab. – Mark Heinlein, NTCA Training Director ASK THE EXPERTS –––––––––––––––––––––––––––––––––––––––––––––––––––– LATICRETE is expanding its product portfolio with VAPOR BAN™ Primer ER. This product is an ASTM F-3010 compliant, epoxy-based, all-in-one mois- ture vapor barrier and primer that saves installers time and speeds up labor on the jobsite, thanks to the product's dual pur- pose. With a quick turnaround time, in as little as three hours, VAPOR BAN Primer ER is ready for self-leveling underlayment placement. VAPOR BAN Primer ER is expected to launch this spring. For more information, visit www.laticrete.com 16 TileLetter | 2019