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Setting tile over tile / Does crack-isolation negate need for expansion joints?
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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.
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QUESTION Is there any publication on the pros and cons of installing tile on top of tile?
ANSWER Tiling over existing tile as a substrate can be a terrific solution for a new tile installation. There are several areas that must be considered before proceeding, such as:
  • Whether the existing substrate is well bonded and able to support a new installation
  • If priming or scarification of the existing tile is needed
  • Correct mortar and/or primer selection and proper application
  • The ability of the existing structure to support the weight of the new installation
  • Adjoining floor elevations
  • And other issues
The NTCA Reference Manual and the Tile Council of North America (TCNA) Handbook are excellent sources of information on this topic. Members of the NTCA own these industry-published methods and best practices. I encourage you to interview and hire an NTCA contractor member for the work you are considering. You can search for one at this link: https://bit.ly/33uFkv3
I also encourage you to interview and hire a Ceramic Tile Education Foundation (CTEF) Certified Tile Installer (CTI). You can search for one at this link: https://bit.ly/3nGcj67
– NTCA Technical Team

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QUESTION I have a wall that is 11′ high by 28′ across. The tiles going on the wall are 4″x40″ and installed horizontally. Do I need to be concerned with expansion joints? This is a primed green board wall. Should we have any expansion joints or should we use a mortar with a crack isolation membrane in it? I have a message to our setting-material rep as well. Yet I am sure he will say use the expensive materials! ANSWER Every tile installation requires expansion joints. The placement and width and material used to fill the joints vary by the type and characteristics of the installation. Environmental conditions are an important consideration. TCNA Handbook Method EJ-171 is the tile industry guide for expansion joints. There is more information in this method than I am able to recount in this email. I suggest reviewing your copy of EJ-171 to familiarize yourself with its requirements. If there is a specification professional (architect, etc.) on this job, you will notice that EJ-171 requires them to provide you with the details of where the joints should be and how they should be constructed. If you don’t have this specification in the plans you were provided, you should ask the specifier for the prints and details you need. – NTCA Technical Team