Concrete, brick, and mortar are incredibly durable, but they’re no match for water. While on a house call, mason Mark McCullough realized the root of a homeowner’s problems with their front steps was exactly that: water getting behind the stair tread, deteriorating the mortar, and heaving the tread forward when it freezes. Luckily, Mark knew just what to do.
How to Repair a Granite Stair Tread
- Start by removing the tread and inspecting the damage. Use a brick trowel to remove all of the deteriorated mortar mix until you reach solid, intact mortar mix. Check the individual bricks to ensure they’re still embedded and remove those that are damaged or loose.
- Remove the loose mortar mix from the mortar joints. Use a masonry chisel to chip the mortar out, reaching a depth of at least ¾-inch. For stubborn mortar, use a grinder with a HEPA vac attached.
- Combine the mortar mix with water in the mixing tub until it reaches a peanut butter-like consistency.
- Repair the joints by scooping mortar onto the brick trowel, aligning it with the mortar joints, and pushing it into the joint with a tuckpointing trowel. Pack the mortar in until it squeezes out and then bevel the joints with a bevel trowel.
- There will be excess mortar on the brick. Use a masonry brush to brush it off the surface of the brick. Then, remove the rest with a wet sponge, making sure to stay on the edge of the brick and not touch the mortar joint.
- Slick the joint using a slicking trowel and maintain pressure on the heel of the trowel.
- Wet the entire tread with a wet sponge. This will prevent the old, dry mortar from sucking the water out of the mortar mix before it can cure properly.
- If any bricks had to be removed, apply a mortar bed to place them in. Apply a bit of mortar to the head of the brick and place it into the mortar bed. Tap the brick with the butt of the trowel until it’s seated in the mortar bed and level with the other bricks around it. Use a level to check, and continue replacing bricks as needed.
- Apply a bed of mortar two inches or so thick on top of the brick and mortar. Use the brick towel to “furrow” the mortar, creating a wavy pattern in the mortar to help with adhesion.
- Mix Portland cement and water in a bucket. This is known as “glue” and helps granite adhere to other masonry surfaces. Apply it to the bottom of the granite tread with a brush, leaving a thin coat.
- Place the granite stair tread onto the mortar bed. Wiggle it back and forth to embed it in the mortar. Make sure that it’s centered on the stairs, level from side to side, and pitched forward. Use a level to ensure that the stair tread is pitched ¼-bubble from back to front, with the front being lower than the back.
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For any intact joints that need to be removed, use the back of the of a brick hammer as a chisel. Wear safety glasses. Use a utility brush to wipe away any excess debris. A grinder and HEPA vac can also be used to help removal. Use ear protection and safety glasses when using the grinder.
There was also a bad joint on the rise above the tread being worked on. Mark removed it with a hammer and chisel while wearing safety glasses. He decided not to use a grinder because the space being worked on was so small.
Repoint bricks using type N premixed mortar. Mix the type N mortar with the correct amount of water in a mixing tub with a trowel. Use a margin trowel and a flat jointer to push the mortar off the trowel and into the joints.
Mark also had to relay the bricks that came off with the stair tread. Spread the same type N mortar with a London brick trowel. Use a rubber mallet and level on the bricks to check their position and range, as in make sure the brick is flush with the existing bricks. Brush the “snots” of each joint using a utility brush. Clean off any excess mortar with a sponge and water, only cleaning the brick. Create a slick by running a convex jointer across the joint for a finished look and to prevent moisture from entering the joint.
You may also opt to rent a power washer to clean the step.
