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Unread 04-17-2021, 06:11 PM   #37
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This the same shower as your previous thread, Dani?
Originally Posted by Dani
Is it easier to meet the above requirements by using CBU, Kerdi board, or drywall with a Kerdi membrane?
Actually, it's easiest to achieve that flatness requirement by "mudding" the walls to create a mortar bed. With any sort of wallboard, you need to bring the framing into plane as Jim pointed out in order to achieve the necessary flatness and it's unlikely even that will result in the needed tolerance without some additional flattening on top of the wallboards.
Originally Posted by Dani
I also understand that a medium-bed mortar should be used when installing large format to tile in order to compensate for irregularities in the tile and substrate.
There are no "medium-bed" mortars, there are thinset mortars that are rated for use in thicker sections than standard thinset mortars, but they're called Large and Heavy Tile (LHT) mortars in the industry. While they can make up for some variations in tile thickness, they are not meant to flatten the substrate. The substrate should meet the requirement you quoted before you begin setting the large format tiles.[quote=Dani]Is there a way to predict how much warping a tile will have (when ordering).../QUOTE] If you order ceramic tiles that meet the standards of ANSI A137.1 you can predict the maximum amount of size difference and warpage. If the manufacturer does not indicate the tiles meet that standard, you can't really predict anything until you have the tiles in hand.
Originally Posted by Dani
I understand that running bond pattern is limited to a maximum 1/3 offset for tiles over 18".
That industry recommendation actually begins with tiles over 15" on any side and is general in nature. It's based upon the expected warpage of tiles that size in general and may or may not apply to your particular tiles. But you have no way of knowing that until you have your tiles in hand and can actually determine their flatness. It's possible your tiles will be sufficiently flat (and you've made your substrate sufficiently flat) you can use a 50 percent offset without unacceptable lippage. The tile manufacturer may also specify a maximum offset for the particular tile or tile line and that is more a requirement than a recommendation.
Originally Posted by Dani
Lastly, I know that there needs to be at least 90% mortar contact and a minimum grout joint of 3/16".
The actual industry requirement in wet areas is a minimum of 95 percent coverage on the back of each tile. The only minimum grout joint width is 1/16th of an inch and that is difficult to achieve with even a well rectified tile in large formats. The industry recommendation is for a grout joint three times the difference in size between the largest and smallest tile in your layout.

The aesthetic considerations are best decided by the customer.

Originally Posted by Dani
Please let me know what other critical technical requirements that I should be discussing with my tile setter.
Is the new shower to be built by the same contractor who built the previous version?

My opinion; worth price charged.

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