Place two of the tiles face-to-face and see how bowed they are...how much they "rock." Some are pretty bad, others not so. If bad, at least a 1/3 overlap is needed...meybe even a 25% deal. Your floor needs to be quite flat for a successful install. If lippage is minimal, I've even butted them together, but an eighth looks good. If they are quite warped, you'll need a larger joint. The colour should be very close to that of the tile, IMHO.

And the floor needs to be STIFF for large format tile. If the bath is on a crawlspace, you need to investigate the joist size and placing in order to calculate how stiff the current floor is and whether or not it needs beefing up before any tile is laid. There's no point in having it all crack a month from installation.

Thanks, I dont know how stiff the floor is, however apparently he is "gutting" the bathroom so i would assume the tile installer can see if anything needs to be placed to make it more stiff. If I'm paying a tile guy to install it, then I would assume he should be able to do a 6"x24" tile without messing it up. That is what I'm paying for after all.

That is correct, however the contractor I am using has been in the business for over 30 years and I know him personally, he wouldn't be bringing in anyone less than a true experienced tile installer.

That is correct, however the contractor I am using has been in the business for over 30 years and I know him personally, he wouldn't be bringing in anyone less than a true experienced tile installer.

I'm sorry but those sound like the famous last words of many an unhappy poster on another tile site.