Porcelain tile is a man-made tile that is one of the hardest, scratch-resistant types of tile produced. It can be used in kitchens, hallways, entryways and bathroom floors without regard to foot traffic. Although it's possible to scratch a porcelain-tile floor if you drag a cast-iron tub across it, the weight of the tub won't damage the tile.
A type of ceramic tile that is man-made with numerous other natural materials, porcelain tile is one of the hardest on the market. It comes in unglazed and glazed formats and is used in a variety of installations. A bathroom floor is the perfect place for porcelain tile, as it will stand up to foot traffic and even the weight of a cast-iron claw-foot bathtub.
Porcelain maxes out at 5 on the Mohs scale, which is the scale of mineral hardness used around the world. This means porcelain is an extremely scratch-resistant material, with granite just above it at 6. Iron, on the other hand, is between a 4 and a 5, which means that it is at least as hard as porcelain. While it is unlikely that the iron will scratch your porcelain, there is a small chance if the porcelain is a lower quality.
The weight of the tub is of no concern in a porcelain tile installation. As long as the proper steps are used during the installation of the tile, there is no need to worry about the tile cracking under the pressure, even when the tub is filled with water. Double sheets of plywood in conjunction with an underlayment and the floor joists themselves provide more than adequate support for a porcelain tile installation.
Dragging the Tub
You are fine installing a claw-foot iron tub on porcelain tile as long as you place the tub carefully. If you drag the tub across the tile you run the risk of scratching the porcelain if it's a lower quality. Claw-foot tubs are quite heavy and require several people to move, but as long as you keep it from dragging across the tile, you will be fine. Once it is placed it won't be going anywhere because of its weight.