FWIW, the 'new' industry term for what used to be called medium bed mortar is now LHT mortar (large and heavy tile). You'll see that in the name on some of the newest formulations of suitable mortar. There was no industry standard defined for medium bed mortar, and larger tile really begged for one - this is it, but it's still in process. I was in a class today, and the industry standards on large tile has been an evolving and moving target, but the latest recommendation contains the following points: - you should use a non-traditional (at least to the USA) trowel. I don't remember the name of the trowel, but it originated in Europe and has weirdly shaped notches that essentially has an angled, tall slot that falls over with minimal actual visual notching, but it does gauge the thinset well, and provide a nice even coverage I may try to take a picture or find a link for one, and if I do, I'll post it. - burn then trowel LHT mortar on the floor - burn then trowel LHT mortar on the back of the tile - use a floor leveling system (I saw MLT's clips in use today, and like it better than the TLS, but there are others and they all should work as well) - use a vibrating sander (no abrasive pad) after setting the tile in place to bed it properly (do not beat it in with a pad and mallet) - this does an amazing job of creating great coverage with no or very minimal gaps in the back of the tile. It is critical to start in the middle of the tile and work outwards, otherwise, you'll potentially get air trapped in the middle that you'll never get out and have a void. - run the trowel on both the tile and the floor (or wall) across the shortest dimension of the tile's surface to allow a path for any trapped air to escape rather than be trapped Now, over the next year, these recommendations may get further refined, but after seeing it performed today, the results are pretty impressive. After setting and cutting some big tiles, they set a big piece of clear plexiglass, and you could see the thinset moving around, the air coming out until the whole sheet looked quite uniform as there were no longer any visible notches - it just looked like it had been applied flat (note, it's impossible to gauge the amount of thinset if you don't use a notched trowel). Most of these big format tile are fairly flexible, and to get a good result without a wavy surface and to minimize lippage, you really do want to use a leveling system with them AND have a very flat floor. If you skimp on the floor prep, expect funky results that will get worse the larger the tile (we played with a 1Mx2.5M tile today -almost 40" by 120", and they make bigger ones - that's a big tile!).