General Tile Discussion

Hello forum, looking forward to hearing your feedback.

I am preparing to tile my kitchen floor, here are the quick facts/background:

• Removed all base cabinets; tile will go all the way to the wall everywhere; planning on a cabinet design that will show some of the tile underneath

• Kitchen is upstairs in a suburban split-level built in 1970; joist type and span have been checked using a calculator and are suitable for porcelain tile with 1.25" subfloor

• Original subfloor was 5/8" tongue and groove playwood, but damaged under the sink and into the pantry adjacent to the sink and loose in other places

• Last weekend, I completed the subfloor rennovation: patched the original subfloor with 5/8" construction grade playwood (left expansion gaps, glued to joists with construction adhesive, screwed new and existing subfloor to joists), then added a second layer of 3/4" tongue-and-groove plywood and screwed it down to the 5/8" layer in a pattern avoiding the joists (expansion gaps on the perimeter and non-T&G seams are all at least 1/8", T&G seams are all snug but not overdriven)

• I have bought 20" hexagon tiles for the floor and matching 12"x 24" rectangles for the trim (planning to cut each of those into three ~4"24" trim pieces); have not yet bought mortar, membrane (planning on using Ditra, but I am open to other options), or grout.

• My immediate next step is to measure for levelness and apply leveler or other leveling technique; I'm expecting more variation than 1/16" based on how the subfloor lined up when it went in, but I'm not expecting a lot more variation than that, so the expectation is that a single pour of leveler is going to be the way to go.

• The kitchen has just a handful of obstacles - the pantry alcove has a weird sub-alcove in it, and none of it is quite square; there is a gas supply that comes up through the floor in the stove corner; there is one floor vent about 4" in from the one exterior wall; that exterior wall has an exterior deck door with a bit of a void between the subfloor and the door threshold; lastly the access to the rest of the house is via two doorless entryways to the dining room and living room, respectively, where the floor is laminate and is expected to end up slightly lower than the tile.

I'm pretty comfortable with my undersatnding of the floor tile process with Ditra membrane after watching enough Internet videos, but my question concerns how to plan for the trim to be added after I do the floor. I have removed damaged drywall behind the sink and in some other places, while in other places, the existing drywall is present, but I may remove some more, and I'd like to do the wall material some time later and add the tile trim after each section of wall is finished.

Since leveler is likely necessary, I expect to make a dam with expanding foam around the permiter, then cut that back to 1/8" and make the floor tile snug against that, using the foam to absorb expansion in the tile. I noticed that Schluter makes a foam wall edge product that can go behind tile trim; would I still use something like that if there is already a foam dam? The Ditra install guide is not super-clear on exactly when the foam layer should be used and when it is redundant.

For areas where I am removing the drywall and there will be a base cabinet, I noted that the Schluter Kerdi board installeasily to the studs and take tile directly, so I could use that for both the trim and backsplash, while leaving the part behind the cabinet that is above the trim and below the backsplash unfinished orange (and yes, the tile trim will sometimes be visible with my cabinet design).

For areas where the existing drywall will remain, can the tile trim be mortared directly on the drywall? Is it worth replacing the bottom edge of each wall with Kerdi Board or hardiback to take the trim?

Penultimately, where the trim meets the tile, caulk or grout? There seems to be an Internet debate about this with no clear answer, but those who favor caulk appear to prefer reduced cracking risk while those who favor grout prefer the grout look. I think I am in the caulk camp.

Lastly, I had a thought that it may be possible to protect the kitchen against a leak or major spill by using shower-like techniques: waterproofing tape between the Ditra seams, Kerdi band and pre-formed corners around the whole perimeter (with at least the bottom section of each wall finished all the way around). It would seem that, with caulking around the vent register and a sufficiently high threshold at the entryways, as well as designing the cabinets to resist water on the floor, the kitchen could be made to hold in a spill of 1/4" or so. Is this silly overkill or an idea worth the hassle and materials cost?

Thanks in advance for your attention and help!