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Surface-applied waterproofing and acceptable lippage allowances
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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 I have been using TCNA B431-20 for shower receptors for years, although I am beginning to run into shower designs that require a topical system based on material availability. I am planning a larger shower than I’m used to; is it acceptable to combine TCNA F141-20 and F145-20 in the same application? I've attached a detail of the specific project for clarification.
ANSWER Thank you for contacting the National Tile Contractors Association. It appears the entire bathroom requires waterproofing and slope. If you are looking for surface-applied waterproofing shower methods you have two options: B421 and B422. You have specified a Noble product for surface-applied waterproofing. They have drain flashing that would connect to a conventional clamping ring drain and could be done in accordance to TCNA method B421. Please investigate this as an option. – NTCA Technical Team

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QUESTION I wanted to find out if there are any industry acceptable allowances or tolerances for lippage of 24"x24"x1/2" thick porcelain tile set over a 2,000-sq.-ft. concrete floor. The GC removed carpet tiles and adhesive. No additional prep or floor-flattening allowances have been budgeted into the job and I’m told there would be no additional budget for any extra steps. The job is for a school district and I would not want to get into any issues with the GC or school district due to lippage. We have not had any discussion about expectations, however, that is something we plan to do.

Over the 12-ft. span of our screed, we get some variation up and down (1/8"+ - 1/4") gaps and peaks. We are not usually a commercial installer. Additionally we are busy and don’t need the job but we were asked to consider doing the work, as there would be additional opportunities in the future. Any advice you could supply me would be greatly appreciated.
ANSWER The American National Standard Specification for the Installation of Ceramic Tile (ANSI A108) defines acceptable lippage for Pressed Floor and Porcelain Tile that meets the specifications for ceramic tile (found in ANSI A137.1) for typical installations of tile to be as follows:
  • All sizes of Pressed Floor and Porcelain Tiles with grout joint widths of 1/16" wide to less than 1/4" wide: Allowable lippage is 1/32".
  • All sizes of Pressed Floor and Porcelain Tiles with grout joint widths of 1/4" wide or greater: Allowable lippage is 1/16".
For reference: 1/32" is roughly the thickness of a credit card. 1/16" is roughly the thickness of a penny.
In addition to these allowable amounts, you can add the inherent warpage found in the tile used in the installation. – NTCA Technical Team