GGCL Guide On How do I select the appropriate mortar for installing porcelain slab

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GGCL Guide On How do I select the appropriate mortar for installing porcelain slab

If you're asking how do I select the appropriate motar for installing porcelain slab tile, realize that you are asking a fundamentally critical question.

You see, when thin set mortar is incorrectly applied, the installation will many times fail. More likely than not, the tile will break - as you see in the image below.

Not a good situation for the customer and a terrible one for everyone involved in installing tile correctly.

Let's focus then on how to properly apply the mortar.

What function do thin set and large and heavy tile mortars serve?

Thin set and the new large and heavy tile (LHT) mortars serve several functions within a tile assembly:

  • They bond to the substrate
  • They support the tile
  • They bond to the back of the tile.

When these three key elements are in place, the tile installation will provide many trouble-free years.

The way you trowel mortar for setting tile makes a big difference. Porcelain slab tiles, in particular, can withstand extra heavy service conditions by taking a lot of impact or point load (think of high heel shoes, pianos, refrigerators or pallet jacks) when installed correctly over a sound substrate. When the mortar is not properly trowelled, it creates unsupported space under the tiles, which become weak spots that can be easily damaged by the same impact or heavy loads.

Here is how to avoid these issues and create a strong tile assembly.

1. Select the right trowel type and notch size!

Make sure you select the appropriate trowel type and notch size.

  • When a “v” notched trowel is used, the narrow point of the mortar does not provide the coverage necessary to properly support the tile.
  • Using a notch which is too small will not allow enough mortar to be applied and likewise will not adequately support the tile.

2. Spread the mortar completely to the layout line!

Make sure to spread the mortar completely up to the layout line.

Installers who stay away from the chalk line to eliminate having mortar squeeze up in the grout joints leave dangerous voids which can result in catastrophic failure, especially in areas subject to high heels, point loads such as pallet jacks, pianos or a refrigerator.

Follow established methods and best practices for installing ceramic tile to avoid long-term issues.

3. Trowel the mortar correctly by playing it straight!

Troweling mortar in one direction in a left to right direction yields the best mortar coverage on the back of the tile. Place the tile into the mortar moving it in a back and forth motion perpendicular to the trowel ridges. This movement collapses the trowel ridges into the valleys leaving very few if any voids in the mortar, which supports the entire back of the tile.

Trowel ridges running in straight lines are much easier to collapse. Furthermore, they assist with air removal to maximize mortar coverage and ensure a strong bond to the tile and substrate.

  • The first step is to “key in” a coat of mortar into the substrate for a good mechanical bond with the flat side of the trowel.
  • Then, add more mortar to the substrate combing the mortar in straight lines, all going in one direction. Combing the trowel ridges in straight lines provides better distribution of the mortar.
  • When installing rectangular (plank) tiles, the trowel ridges should go in the same direction as the short side of the tile. This allows better air release from under the tile since the air travels a much shorter distance when you bed the tile.
  • Be careful not to leave any voids along chalk lines or between tiles.
  • Use a trowel that will help you achieve a continuous minimum 3/32” coverage. Larger tiles most often require deeper trowels.

In the photo below, you can see that two adjacent tiles are broken with those pieces being much lower than the unbroken tile around them. The cause of the failure was multi-faceted. The installer did not spread the mortar with a recommended trowel, there was no mortar at the edge of the tile, and the installer was not qualified. The installer in this case had been placing tile for a grand total of three weeks.