Has your installer told you that your space can successfully accept a 35 x35 tile without lippage? Is the tile rectified so that you can expect a 1/16" grout line with thin set? The more variation in the subfloor, the larger the grout lines will be.

Those are BIG tiles. Large Format Tiles (LFT) are anything with a SINGLE SIDE that is more than 15". Your choice CERTAINLY fits the bill. The tile setter needs to be WELL EDUCATED with this product (ahem...s/he paid for and traveled to the training centre and took the 3 day course).

And the homeowner needs to understand that 1/16" grout lines are probably NOT possible with LFT tiles. The "best practices" will indicate at least 1/8" grout line or bigger is NORMAL for LFT (the installation instructions for the tile will dictate what is ALLOWED).

And IF (big 'if) the smaller grout line is allowed, then SERIOUS subfloor preparation is needed. And by serious I mean EXPENSIVE. As in 'almost the same cost as the tile' type of expensive (per square foot).

Please speak with your designer, the tile EXPERT who will sell you the tiles and then read the INSTALLATION instructions for your chosen tile BEFORE you PURCHASE anything. And Home Depot (or any other big box store) is NOT a 'tile expert'. You will need to purchase these tiles from a high-end store who offer installation 'in-house'.

Grout matching should not be an issue. Using a high-end grout (again it will be DICTATED by the tile manufacturer) that is stain resistant is not a problem. Actually the colour of the grout could be the least of the problems. There could be some real doozies in the future should the wrong installation format be used (small grout lines, improper subfloor prep and improper grout choice).

Please reach out to your local, high-end tile and stone store for more information about your preferred product. Have them COME TO YOUR HOUSE before offering a quote for installation. Only after a walk-through of your space will you get an honest/real quote with appropriate numbers. Do not trust anyone who sells these with a "square foot installed" price. There is no way to know the cost of install without walking through your front door.

We have gray 12 X 24 limestone tiles with thin grout lines. They are 1/8". The gray grout matches perfectly. You'd say it's medium gray. It is not noticeably darker in the wear areas. It still looks like new, 2 or 3 years later. And we have many kids and many dogs, and certainly not obsessed with keeping the floors clean. I think Perhaps you might be overthinking your worry about gray grout turning black with dirt.

Thank you for the replies.

The tile is rectified, according to the manufacturer, porcelanosa. The installer mentioned the sub floor prep work that needs to take place, although they didn't go into as much detail as you have mentioned, but I will definitely be inquiring further.

I am much less worried about the grout color now - so thank you for that... but now I have other worries regarding the install! Porcelanosa does not offer in house install, and the designer I worked with did not mention any special accommodations that need to be made for the large format tile, I guess they just want to sell the tile and move on.

Thank you again for the information. It is super helpful. :)

Be aware that some of these extra large format tiles from Europe have issues with installers have VERY LITTLE training. There have been horror stories about installer knowledge (or lack thereof) for these extra large tiles.

In Europe, the tile setters are SENT to the training facility in Spain (yah...not a bad way to get your training) to spend 3 days to 2 weeks learning how to install these Divas.

Please be sure to hire a CERTIFIED Tile setter (check their credentials and their training and certificates) who has had manufacturer-SPECIFIC training with these tiles. You do NOT want your project to be the learning curve for your installer.