Tiling a "wet'" room (such as a laundry room, bathroom, mud room or potting room) presents a special challenge. Floor tile is generally moisture-resistant, but if there's going to be frequent moisture in the room, you might still have issues with plywood underlayment or unsealed grout. Laying down a waterproof cement board underlayment will ensure that the base under the tile never gets soggy and soft. Grout sealant will make the grout lines as watertight as the tiles themselves.
Lay a sheet of cement board in one corner of the room. Trace the edge of the board with a pencil onto the floor. Lift the board and spread thinset mortar over area, using a notched trowel. Press the board back down. Secure it by sinking screws every 20 or 25 cm (8 or 10 inches) over the whole surface.
Repeat the process to lay cement board over the rest of the floor. Set the boards in rows, arranging them so there are no four-way intersections. Make any necessary cuts along the walls by scoring the surface with a razor knife and then snapping it at the scored line. Cover the whole floor.
Let the boards set in the mortar overnight. Lay mesh plasterboard tape over the seams between the boards. Use a plasterboard knife to spread thinset mortar over the tape. Get it smooth and flat. Let it set overnight.
Divide the cement board surface of the floor into four quadrants, using a chalk snapline to lay two intersecting lines from wall to wall in both directions. Spread thinset mortar about a square metre (a few square feet) at the centre, covering the intersection. The lines should still be visible through the mortar.
Set the first four tiles in place at the intersection, putting spacers between them. Build out from there, spreading more mortar as needed. Lay the tiles along the lines and into a grid pattern, working toward the walls. Cut the tiles around the perimeter on a tile cutter to fit.
Let the tiles set overnight. Pull out the spacers. Grout the floor with a grout float, spreading it over the surface and forcing it into the lines. Wipe up the excess grout with a damp sponge.
Let the grout cure for 48 hours. Coat the grout lines in grout sealant, applying it with the applicator bottle.