Kevin-- with large format rectified porcelain, you're going to have a couple of problems. First, for a joint that small, you're going to have sizing problems-- even with rectified porcelain. Secondly, you're going to have a severe problem with warpage in the tile. I'm assuming you're going to lay this in brick pattern? There have been directives issued just in the last couple of months, first from the TCNA (Tile Council of North America) as well as a bulletin that went out from Daltile to all their accounts that large format rectified porcelain shoujld no longer be used in a brick pattern unless you use a MINIMUM 3/16" grout joint. The reason is that the warping of the tiles will cause unacceptable lippage from one tile to the next, where going from one row to the next, the ends of the tiles line up with the middle of the one next to them. I went through this last winter with a much smaller "large format" tile (12x18), where the architect for the project had already heard about this problem. What I ended up doing was using what could be described as a "1/3 offset brick joint". IOW, instead of aligning the ends of the tiles in one row with the middle of the tile in the next, I set it so that they would align with 1/3 of the next tile. Here's a picture so you see what I mean. But if you notice, it's STILL a 3/16" grout joint (by architect's request for the reason of warpage), even with the 1/3 offset:

Thanks, Bill--that's exactly the sort of thing you don't hear about as a DIY'er until it's too late! I'm not planning on offsetting the tile layout, though. But it sounds like a 1/16 might be a better idea. If the tiles aren't offset, is that going to be enough to prevent lippage?

On the same job, we're going to have to put in an expansion joint mid-field, as the largest area is an L-shape, 26' wide on the short side and 40' on the long side. Do you have any recommendations about how to deal with a break in the 40' span?

Thanks--your advice on this board has been consistently invaluable!

Kevin

Thanks Bill for always helping all of us. We all appreciate it and reading posts of others helps us also for future projects. Anyone that installs tile and does it well, has talent I have learned from the nightmare tile job I had last year. But I do love my Porcelain tile and when I am ready to do my kitchen, I will know that in Northern NJ, everything is very expensive. If someone's price is too low, I will question it. I will also want to see their work in person.