Double gluing Dekton slabs
I have a question about a Dekton application. When double gluing, it was indicated to use a toothed trowel to apply mortar to the tile. Lately some suppliers and UNE EN 138002 recommend applying mortar with a smooth trowel. What do Tile Council of North America (TCNA) standards say about this?
ANSWER The American National Standard Specifications for installing Gauged Porcelain Tiles/Panels/Slabs (GPTP/S) such as Cosentino Dekton are found in ANSI A108.19 (Interior installations) and ANSI A108.20 (Exterior installations). These documents provide step by step instructions for installing GPTP/S.

ANSI A108.19 Section 12.0 Application of Bonding Mortar describes the recommended troweling process in detail.
Collins Tile & Stone joined with David Allen Company to install Dekton panels in this commercial showroom.
  • A108.19 Subsection 12.6 states “Using a notched trowel of type and size recommended by mortar and tile manufacturers, comb mortar onto substrate and tile uniformly with no bare spots.”
  • A108.19 Subsection 13.0 lists the additional steps for embedding the tile after troweling.
  • A108.19 Subsection 14.0 states the required mortar coverage for properly supporting the tile.
The application of the adhesive bond coat will vary somewhat depending on the adhesive being used and the panel being installed. Typically, the panel manufacturer conducts in-house testing by installing their panels with a variety of adhesives from a variety of setting materials manufacturers. The results of the testing will determine the combination of trowel types and sizes for the substrate and the panel to achieve optimum bond coat coverage for a variety of adhesives.
In addition to the Installation standards, methods for installing GPTP/S are published in the TCNA Handbook for Gauged Porcelain Tiles and GPTP/Slabs Installation.
It’s recommended that you purchase both of these documents from the NTCA store:: ANSI A137.3 / A108.19 / A108.20: TCNA Handbook for Gauged Porcelain Tiles and GPTP/Slabs Installation:
    Electronic versions are available for purchase from the Tile Council of North America at
    High moisture measurements in recent shower installs
    I am an architect and have a question about moisture in showers. We designed four showers in an apartment completed in September 2023 that appear to have been built properly as far as we can tell from site observations and speaking to the contractors.
    Our client used a pinless moisture meter on the floor of their four showers (PROTIMETER SurveyMaster BLD5365) and found a high moisture level 3/4" below the finish surface. Beyond the showers the finish floor has a lower moisture level. There is no leakage nor any damage – just this measure of high moisture. I spoke with the thinset mortar manufacturer and they said moisture will not degrade the thinset. The client measured the moisture while measuring an unrelated moisture issue.
    My question is whether there is any issue with moisture being detected in a shower pan? I have never had a client measure moisture in this way. Is there any data on acceptable levels of moisture? Could the lead pan trigger the moisture meter to give false readings? Client is concerned mold will grow. Two showers are never used and I have no idea where moisture could be coming from.
    It stands to reason that showers have a higher moisture content than the dry area beyond. Our team would expect the moisture amounts to be higher in a packed mud bed as it takes a while for the water to weep through. If the showers that are being used are not properly sloped to drain or if there is a slow draining mud pack or weep holes are beginning to clog, these showers may be retaining more moisture than we would normally expect. If there are no visible leaks and no long-lasting discoloration with the grout or stone or no unusual smells we don’t see a cause for concern. Since it sounds like there are no leaks or any immediate concerns we would assume the showers are functioning properly.
    We do not have any knowledge of lead pans affecting moisture content beneath the tile layer unless there is a problem with the slope to drain with the drain being higher than the pitch where slope meets it.
    We agree with the thinset manufacturer – the moisture won’t affect the thinset mortar bond coat.
    We feel the potential for mold growth is limited but could possibly grow on the top surfaces when fed by soaps or shampoos and organic materials; this could be easily prevented by routine cleaning.