Drill ¼-inch holes along the mortar lines between the bricks. Make the holes 3 inches deep and about 1 inch apart. Fill each hole with a cedar plug; hit the top of each plug with a rubber mallet until it is about even with the bricks.
Cover all of the bricks with horizontal spruce boards. Line up the edge of each board with the nearest mortar line. Screw 2-inch drywall screws through the edges of the boards and into the cedar plugs behind them.
Sand the surface of the spruce once the brick is completely covered. Make sure there are no rough or splintered areas and that the whole facing is level. Wipe the surface area with a dry rag to remove dust.
Prepare the drywall for hanging. Determine where cuts need to be made or where a piece needs to be resized. Cut or trim the drywall as needed with a drywall saw. Hang all of the prepared drywall with drywall screws so that the surrounding area of the fireplace is completely covered and all of the seams remain aligned.
Spread joint compound along all of the seams using a straight putty knife. Keep the application thin while covering each joint completely. Smooth each joint with the knife so that it is straight and even.
Cut strips of fiberglass joint tape to fit each seam. Apply the strips over the joint compound while it is still damp. Work slowly and keep each piece straight and unwrinkled from end to end.
Let the seams dry completely. Spread drywall mud over the entire refaced area with a clean, straight putty knife. Apply the first layer moderately, then add a second, thicker layer to achieve a smooth, uniform finish all over the refaced area.
Allow the mud to set overnight. Examine the surface for any rough patches and sand these lightly. Finish your resurfaced area as you wish.