Find the color of epoxy that you would like to see on your fireplace. Epoxy can be purchase in hardware or home stores and comes in a range of colors and finishes. The epoxy will likely come in two parts, the coating and the activator, which will need to be mixed together before use.
The stone fireplace must first be cleaned of all dirt, ash and grime. Make sure this is done thoroughly because once the epoxy is applied it cannot be removed. Use heavy-duty sponges, scrub brushes and cleanser to make sure that the stone is sparkling clean.
Put on a face mask and heavy-duty gloves before you get started, as epoxy can be irritating to the skin and eyes. Mix a small amount of the epoxy coating and activator together. Apply it immediately to the fireplace stone using a sponge. Spread the epoxy evenly over the stone until the fireplace is covered, mixing the epoxy as needed.
Allow the fireplace to dry for at least 12 hours. At this time determine whether the fireplace is the color that you want. If so, let it dry for an additional 24 hours before using the fireplace. If it is not the correct color, apply another coat of epoxy and repeat the drying process. Continue applying epoxy coats until the fireplace is the correct color and finish.