Do I have to seal my grout?

Yes!

The two main types of grout are sanded and unsanded, sanded is used in larger grout joints and unsanded in smaller joints. The sand is added to the grout to give it strength, but also leaves a rough texture. This porous rough texture absorbs spills, dirty mop water, outdoor soil and so on, making it difficult to clean. In no time the grout will be stained, discolored, and just plain ugly. Using a quality sealer on the grout will help prevent permanent staining, as well as make cleaning easier. The misunderstanding is… people think sealer will keep their grout clean. The fact is sealer will only provide a barrier, thus making cleaning easier and permanent damage less likely, soil will still find its way to the floor, if I had the answer to preventing that, I would be a hero, and probably out of business. The unsanded grout ussually found on walls, and in showers, is much less porus, but still can benifit from sealer especially in a shower. There are often minerals in the water that can even leave unsanded grout stained after time, especially white grout.