Many tiles, including some that are made from porcelain, have a layer of glass added to the surface (we call this process glazing) that protects the biscuit (or body) of the tile from staining and damage.
As porcelain is extremely strong and durable as well as being virtually non-porous, meaning that it doesn't absorb liquids, porcelain tiles don't need a layer of glaze to protect them. The advantage of this is that the surface of the tile can be polished to any level of shininess from a light 'lappato' finish right up to the high shine we usually think of when we talk about 'polished porcelain.'
Although the tiles are non-porous, they can contain microscopic bubbles under their surface. During polishing these can get opened up and effectively become tiny cups on the surface of the tile.
Often when polished porcelain appears stained, all that has happened is that a liquid has been spilled and is filling these cups. As regular cleaning doesn't wash the liquid out of the cups, it can seem that the tile is stained. In fact, it can be removed with the right kind of washing, but can also be avoided altogether with correct sealing of the tile.
Polished porcelain tiles should be sealed with a special sealer when they are laid. Instead of coating the surface, this sealer fills the microscopic cups, not allowing anything else to get in. A spill may stain or appear to stain a polished porcelain tile if:
The tiles were not properly cleaned and sealed when they were laid.
A cheap or inferior sealer was used. Poor quality sealers can be washed out with regular cleaning.
A staining type spill has been left on for an extended period: long enough to penetrate the sealer. As with anything, all spills should be cleaned up quickly.
If your floor has not been sealed, it is simply a matter of:
Remove heavy stains with poultice, water, and a white nylon scouring pad. Follow the instructions and don't rush the job.
Thoroughly clean the floor with Heavy Duty Tile and Grout Cleaner. This will help make sure you don't have dirty grout too.
Seal with Pro-Solve 10.
If you believe the floor was already sealed:
Contact your tiler to identify the product that was used. If it turns out the floor wasn't sealed, follow the directions above.
Follow up with the manufacturer to find out what can be done to remove the stain. Beaumont Tiles recommends using Heavy Duty Tile and Grout Cleaner. For bad staining use poultice, water, and a white nylon scouring pad. Follow the instructions and don't rush the job.
As with regular cleaning of any tiles, use only warm water with a small amount of disinfectant added. The only prepared cleaner that should ever be used regularly is Concentrated Tile Cleaner. This is designed specifically for cleaning tiles such as sealed porcelain tiles.
Learn how to clean tiles for the best results.
The tile shop (or tiler) said that sealer wasn't necessary!
Some polished porcelain is factory pre-sealed and does not need sealing, but if anyone tries to tell you not to seal (or protect) unsealed porcelain, do not listen to them.