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Hayder Seeks: Mortar Mishaps

09.27.18   Hayder H. Al-Hilal, PE, SMSI, CIP-1, CCI-2, Level 1 Thermographer | More by this Author

Hayder Seeks: Mortar Mishaps

FAQ: Hayder, my exterior tiles sound hollow when I walk on them, and they seem to be debonding. I just had them installed, what might the problem be?

ANSWER: According to the Tile Council of North America (TCNA) and the American National Standards Institute (ANSI) guidelines, a minimum 95% mortar contact is required between the tile and substrate below for exterior tiles. Proper mortar troweling is required to achieve this coverage. Improper troweling will result in voids under tile making it more susceptible to damage from live loads and moisture-related issues, such as efflorescence staining and freeze-thaw damages. Hence, proper mortar application is critical to preventing tile failures.

The picture below shows an example of improper mortar troweling. Trowel notches indicated a swirling combing pattern. Inadequate bond was observed between the tile and adhesive mortar.

 

The following recommendations will help in achieving sufficient mortar coverage:

  • Use the trowel’s flat side to key a coat of mortar into the substrate.
  • Apply additional mortar and use the trowel’s notched side to comb the mortar in a single direction, parallel to the tile’s shortest dimension. Do not swirl the mortar. Mortar swirling will lead to trapped air within the swirled mortar ridges, leaving voids under tiles.
  • Spread as much mortar as can be tiled prior to the product skinning over.
  • Back butter (applying mortar to the tile backside) to minimize voids due to tile warpage or substrate defects. Back butter the entire backside using the trowel’s flat side. Do not spot apply the mortar.
  • During installation, move the tile in one direction, perpendicular to the mortar ridges. Do not twist the tile.
  • Confirm proper mortar coverage by periodic removal of tiles to check the coverage rate. Adjust trowel’s size, as required, to achieve the required mortar coverage.

This video from the National Tile Contractors Association (NCTA) demonstrates how and why the proper mortar application is critical.

Proper mortar application, using the NTCA-recommended tile setting method, is critical to providing a long-lasting, durable tile system, and to avoiding frustrating and costly tile system failures.

If your exterior tiles are exhibiting hollow-sound or debonding, or if you are planning to install a new tile system and would like an active quality control/quality assurance program during tiles installation, SME can help. Contact Hayder Al-Hilal for more information.



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