Sealing brick prevents breakdown.
It also makes the surface of the brick easier to clean. There are two types of clear sealers for masonry — film-forming and penetrating. Penetrating sealer, which soaks into the brick, is a better choice because many brands have been heat tested and are fire resistant. Many silicone-based films, on the other hand, can melt, wear off or ignite when close to a heat source for a prolonged length of time. Always start with a squeaky-clean fireplace before sealing; clean all dirt and soot from the bricks and have your chimney professionally cleaned.
Put on safety goggles. Open the windows nearest the fireplace to provide ventilation.
Use a shop vac to remove residual dust, dirt or debris from the bricks, making sure to vacuum the mortar well.
Place a can of sealer into a hand-spraying unit, following the manufacturer’s directions for use.
Apply the sealer to the brick using even spray strokes across the entire brick fireplace.
Allow the sealer to soak into the brick and dry, as directed by the manufacturer.
Apply a second coat, if desired.