Clean off any soot with a 2-to-1 mixture of water and degreasing cleanser using a nylon scrub brush. Wipe off excess cleanser with a damp towel and let the brick dry overnight.
Mix together equal parts of water and white flat latex paint. Stir the mixture with a paint stick until the consistency is uniform throughout. Mentally divide the fireplace surround into quarters.
Apply whitewash to 1/4 of the surround at a time using a paintbrush. Wipe away the white wash in areas where it is too thick using a rag. Add more whitewash or remove more to tone the brick as you like and let the surround dry 24 to 48 hours before using the fireplace.