Then there should be no problem. The only problem with large format rectified tile is that it tends to "bow" slightly in the center, so that if you set it in a 50% brick joint, the centers of the tile will always be higher than the edges, causing a definite fail in the "credit card test". But if you're setting it in a standard soldier coursing, there should be no problem.

My primary concern is why are the tiles lifting in the first place? Was the base ever sealed with anything? And you said this is a "concrete pan", is this deck mud over a membrane, or are you going over a slab? There's a membrane somewhere under the "concrete", right? Just asking. The thinset should not be from an old bag that's been laying around for months and months. Old thinset can undergo partial hydration in the bag, weakening the final bond strength. If your thinset is old, go crazy and splurge $15-$30 on a new bag. The thinset should be mixed so it spreads like soft butter; loose enough to spread, but tight enough so that when you do spread it with a notched trowel, the ridges hold and don't flow out and collapse. The idea with using a 1/4" notched trowel is that after the tile compresses the thinset, the 1/4" high ridge is compressed to a 1/8" thick setting bed of thinset, evenly coating the underside of the tile. You want to bed the tiles in the thinset so you compress the thinset ridges down, but you don't want to mash them so hard that you squeeze out all the thinset from between the tile and the substrate. All that said...yes, clean off the old thinset so that there is no loose powder or clumps adhered to the bed. You want it smooth. You can have a residue of old thinset on it, but you want it smooth. If youre using Custom thinset, then as Bill mentioned, use a modified thinset for your next attempt. Either VersaBond (lightly modfied) or FlexBond (highly modfied). My apologies if I'm being too much "Tile 101" on this reply, but even dryset will provide a good bond to a properly prepared base. Mongo

Blondelle, it's the edge meeting at right angles. I've got a few of those - a couple are on half-tiled walls, so I've got to go around the corner *and* finish off nicely on the top edge (and top corner). Then there are a couple of corners that also transition from half-height to full-height in the tub/shower. The "cuarto de cana" (quarter round) and "angulo cuarto de cana" (quarter round corner - can't do the tildes!) pieces, along with some bullnose, would solve the problem for me, but I'm not sure I can get those pieces for my preferred tile (and possibly not even for my less-preferred tile) in time for work to start on 9/29. Bill, I understand how to use bullnose to finish off one side of a corner edge and have the other side butt into it... but how do I finish off the top of the corner when it's a half-tiled wall? Do I just miter the bullnose strips along the top? Can I miter the (possibly glass) border tile beneath the bullnose, and then just use the vertical bullnose/butt technique down the rest of the side? (Hope that made sense... I'm just learning this stuff!)

Bill V - I found one of your comments in an old GW post from 2008. I copied and pasted below. So I'm thinking unsanded. If I am wrong, please let me know! Thank you so much for all of your help! As for the explanation of the different grouts, I just posted this in an FAQ thread on the gallery side of the bathrooms forum. Here it is, copied and pasted: Although there are others, for all intents and purposes, there are two kinds of grout-- portland cement based, and epoxy. The portland cement based grouts are the conventional grouts that have been around for millenniums. Although in the last few decades, they've been modified with latex and other polymers to make them stronger and more resistant to mold and mildew, they're basically the very same grouts that have been used since Greek and Roman days. There are two kinds of portland cement based grouts. One is sanded, and the other unsanded. The only difference between the two is, as their names imply, the sand. The ONLY thing that determines which grout should be used is the joint size. NOT the glaze, NOT aesthetics, NOT the material (ceramic vs. glass or polished marble), NONE of those. I'll repeat-- the ONLY thing that determines which is used, is the joint size. Anything under an 1/8" takes unsanded grout. Anything 1/8" or bigger, you use sanded grout. If you use unsanded grout in larger joints, the cement in the grout will shrink way too much as the water evaporates out of it, and the joints will end up shrinking and cracking bigtime. If you try using sanded grout in smaller joints, the grains of sand will literally clog the top of the joint, and not allow the grout to get down INTO the joint, and the grout will flake off in a matter of days.