First, make sure the floor meets a deflection of no more than L360. I would probably use Ditra to help with flatness (to a degree) act as an isolation membrane and contain spills.

Check for the degree of "cupping" by putting two of them face-to-face and see if there is substantial "rocking" of the tiles. If minimal, you can probably get by with HD's Versabond.

Try to pick an installer that has experience with plank tile and insist on a 1/3 stagger to minimize lippage. 1/2 stagger WILL accentuate the problem. (don't ask how I know)

A leveling system can help the final "tweaking" of the floor and may or may not be necessary...depending on the tile, the floor and the setter. It is not a cure-all.....

Stonetech, thank you!
Really appreciate your help!

I've done some reading on ditra for interior and exterior locations after reading your post.
So the layers would be (bottom to top)

Plywood ( is there a minimum thickness, some website mention 2 layers min 1 1/8 inches , why is that or is that only for exterior?)
modified thinset
Ditra
unmodified thinset
Porcelain Tile

appreciate any help as always. Meeting contractor tomorrow.

This post was edited by scrappy25 on Mon, Sep 1, 14 at 16:24

scrappy25:

Lippage is installer error, except that that must be traded off for curved tile, it has little to to with underlayment. You could have a dead flat level floor, but if the installer doesn't know what he's doing, you could have unnecessary lippage.

I'd look to my homeowner's insurance before I'd worry about waterproofing, but Ditra is always a good idea.

Our kitchen has been done with porcelain plank tile in a beautiful herringbone pattern. Pattern is so beautiful that I had to change my cabinet choices because the floor became such a strong focal point. But I don't consider that a serious problem.

What I do wish we would have done differently is ask for a darker grout. Tiler used Fusion Pro which is somewhat knew and is touted to eliminate problems with keeping grout clean - so far so good. I thought the grout was a match but wish I would have gone against my intuition and asked for something that looked a little too dark. Not sure if Fusion Pro dries light or what but wanted to post here (I have gotten such great tips here...)

Thanks Treb and elphaba

Treb- The Ditra may be overkill but might add peace of mind especially fo the accompanying screened porch installation. Your comments make me more comfortable if the contractor says it is not needed in the kitchen. Those dishwasher/icemaker floods are what decided me against extending the hardwood into the kitchen.

Elphaba- I have heard that grout tends to dry light , thanks for the warning! I will ask my contractor to do a test run before doing the whole floor thanks.