How to Seal Brick on a Chimney
- 1). Inspect the chimney for mortar joint cracks, splits or crumbling. Repair damage prior to sealing. Sealants with not effectively cover large gaps. Chip away damaged mortar with a masonry chisel and hammer. Replace the joint with new mortar.
- 2). Clean the bricks and mortar joints with detergent and water. Scrub away surface stains, dirt and debris with a stiff scrub brush. Use plain water to rinse the brick and mortar surfaces well. Allow the masonry to dry completely. Moisture and dampness will affect the level of sealant penetration.
- 3). Stir a siloxane-based penetrating sealant with a mixer bit attached to a power drill.
- 4). Apply a penetrating sealant by brush, roller or sprayer to the entire surface of the chimney. Allow the penetrating sealer to dry completely, generally six to eight hours. Apply a second coat of penetrating sealer to the bricks and mortar to complete the seal. A third coat is not a requirement, but if you have enough sealant leftover, brush, spray or roll on a third coat after eight to 10 hours because sealants lose effectiveness after opening.