Place the dropcloth around the hearth to keep the area clean while you tile. Wipe the bricks down with a firm wire brush to remove any loose bits from the mortar or bricks.
Soak a cloth in plain white vinegar and wring out. Scrub areas with soot to remove. Once done, allow the bricks to dry for at least 24 hours.
Mix the thinset in a mixing tub according to package instructions. Scoop thinset with your flat-edged trowel and apply it onto the brick surface. Use enough thinset to completely cover the bricks and pack into grout lines to create a smooth surface. Cover the entire fireplace with one coat and allow to dry for 24 hours.
Attach the 1-by-4 board across the entire length of the fireplace, directly over the firebox. This will provide you with a ledge to hold up tiles over the firebox to prevent slipping as you work. Nail each end of the board to the wall.
Mix a new batch of thinset in the tub to begin attaching tile. Work in small sections so the thinset won't dry before you attach the tile. Using the notched trowel, scoop out thinset and spread onto the fireplace. Place a tile onto the thinset, and press firmly with the hand to secure it in place. Add a tile spacer and continue tiling the entire fireplace, working from the top and moving down. Allow the thinset to dry for 24 hours.
Mix the grout according to package instructions, and scoop out with a rubber float. Apply to the tile at a 45-degree angle, getting enough on the surface to fill grout lines but not leaving too much on the tile surface itself. Grout the entire fireplace.
Wet a sponge with water and wring out thoroughly. Clean off the tile once the grout begins to dry, which you will notice when the tile surface becomes hazy-looking. Clean off the tile and smooth down grout lines, being careful not to remove too much from the lines. Allow to dry for at least 12 hours.