Measure the area on your brick fireplace where you want to place the Sheetrock. Mark the measurements onto the brick with chalk to use as a guide during installation.
Draw the measurement of the area onto the Sheetrock. Cut the Sheetrock by scoring the measurement marks with a sharp utility knife. Snap the Sheetrock at the score line to separate the excess from the piece you need.
Apply thick areas of drywall compound throughout the back of the Sheetrock, spacing the sections evenly throughout. Press the drywall onto the section of brick fireplace.
Install masonry nails through the Sheetrock and into the brick beneath to hold it in place during the Sheetrock drying process.
Let the drywall compound dry for at least 24 hours before finishing the Sheetrock in the method of choice, whether it’s painting or tiling.