Choosing to lay tile on a concrete slab is a good idea. The concrete makes a firm surface that the tile requires. You will have to clean and prepare the concrete surface before installing any tile. Deciding whether to seal the concrete is part of the preparation.
You need to clean any paint, sealant or glues from the surface of the concrete. Concrete sealant or paint prevents the adhesive from sticking properly. Once you clean all these agents off the top of concrete, you can begin preparing the surface. Take some water and mop the surface to remove any dirt, dust or small debris. You will need to use an acid-based solution, like muriatic acid, to rough up the surface if the top of the concrete is still smooth. Let the surface of the concrete completely dry before installing tile.
You need to check the surface of the concrete to ensure it is level. Any place that is cracked, chipped or beveled, must have concrete patch or leveling compound installed. Mix the compound and apply to all trouble areas. Use a level to ensure the repairs remain even with the rest of the concrete surface.
You must use a trowel with notches on at least one side to apply the tile adhesive to the concrete. Adhesive sticks to the rough surface of the concrete and acts as a sealant for the pores of the concrete surface. The notched trowel forms parallel ribs so the tile can be pushed into the surface. The ribs will collapse making a bed for the tile, between the surface of the concrete and bottom of the tile. Make sure the surface of the concrete is dry before applying any adhesive. Different types of tile must be installed for outdoor patios. The tile is designed to resist the elements, while handling direct sunlight and frost better than indoor tiles.
After laying all the tile over the surface of the concrete slab, allow the tile to rest for 24 hours before finishing the tile. Use grout to fill in the cracks between the tiles. Apply the grout and wipe off the excess grout with a damp or wet sponge. Let the grout dry for about 1 hour, then use the wet sponge to remove any grout film left on the surface of the tile. If you install tile in any wet areas of the home, seal the edges of the tile with caulk.