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Working with mosaics
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Ask the Experts Q&As are culled from member inquiries to NTCA’s Technical Support staff. To become a member and make use of personal, targeted answers from Technical Support staff to your installation questions, contact Jim Olson.
QUESTION Question on shower pan mosaics: When using a bonded drain flange, I have found that many times the drain grate is taller/thicker than the mosaic tile. For the pan to drain properly, the tiles have to be ever so slightly above that grate. However, if you put down the amount of mortar needed to hold the tile in place, the tiles rest below the rim of the grate.
We are not supposed to build up with thinset, but what else are we able to do in order to get the tile to the correct height? I have not seen anything in the manual that addresses this.
Installation Instructions for LATICRETE® HYDRO BAN® Shower Pan Kit
ANSWER You are correct – I would not build up with thinset. I suggest your best option is to speak to the drain manufacturer to ask if they have alternative grates with lower profiles for thinner tile. Assuming you are using foam pans, I am not aware of any other material that would make sense to add on top of the entire pan to build up height. If making mud pans, you can likely correct for the height difference.  If making mud pans – and you want to stick with surface-applied membrane – you could switch to clamping ring drain using the divot method. This method is shown in TCNA Handbook Method B422. It might help you resolve the finished tile to drain height difference for thinner tiles. – NTCA Technical Team QUESTION The situation: mosaic tile layout. 1" hex tile, dot connected. Custom layout, white sheets and black sheets. Making a black border and stars interspersed in the field. (Picture is second try; working third now.) We have laid this out twice and are working on the third rendition. Joints are a bear to keep even, straight and square. Is it just a matter of working with them as we install them to keep everything straight? We know that we can cut full sheets down and work the joints. We do not think there is a trick or technique, just time and patience. Are we wrong to think that?
ANSWER Here are 10 steps that should help:
  1. A flat, suitable substrate is required.
  2. Properly-mixed mortar.
  3. Clean substrate
  4. Key the mortar into the substrate with the flat side of the trowel.
  5. Select the trowel that when correctly used will apply adequate mortar to achieve 80% - 95% or hopefully full coverage (through any mesh) without ending up with too thick of a bond coat that will allow mortar to squeeze through the joints or allow the tiles to slump.
  6. Flatten mortar ridges with the flat side of a trowel.
  7. Set the sheets and individual tiles with care and patience.
  8. Don’t spread the mortar or knock down the ridges too far in advance.
  9. Plan for time, patience and care in setting the sheets and individual tiles.
  10. Using large tweezers and small wedges can help hold tiles in position.
I hope this helps! – NTCA Technical Team