How to Repair Flagstone Steps

Mason Mark McCullough helps a homeowner fix their flagstone entryway. With a few broken joints, several of the stones in the entryway are starting to come loose, so Mark chips out of the old joints and lays the stone back in new mortar beds before showing the homeowner how to blend the repair in with a sponge. Then, Mark finishes the job by installing a soft joint.

How To Repair Flagstone Steps

1. Use the hammer and cold chisel to break the mortar bond around the loose stone. Hold the chisel upright and strike the butt with the hammer to crush the joint. Once loose, slide the chisel under the flagstone and remove it from the joint.
2. Use the chisel and hammer to remove the existing mortar bed. Also, remove any mortar around the bordering stone. Clear away any dust and loose grit with the masonry brush or stiff bristle brush.
3. Pour the mortar mix into the mortar trough. Add water according to the manufacturer’s instructions and carefully mix the water and mortar together. Work slowly to prevent kicking up too much dust. Tip: Add slightly less water than the manufacturer suggests at first, slowly adding more water until the mortar has a stiff oatmeal-like consistency.
4. Apply a concrete bonding agent to the existing concrete to ensure that the existing concrete does not pull all of the moisture from the mortar too quickly. Paint it onto the surface and the edges of the existing stone and mortar so everything can bond together.
5. Trowel the mortar mix onto the floor. Create furrows with the edge of the masonry trowel by lightly pressing down at an angle until small ridges form. Make sure to work mortar until the bordering stones to ensure there is a solid bond.
6. Place the field stone into the bed of mortar and wiggle them into place so they’re at the same height as the existing floor. This will likely push mortar up around the edge of the stone. Remove the excess mortar with the trowel. If the stone is on the edge of a step, pack mortar mix under the stone being careful not to lift it before it has a chance to set.
7. Use the sponge, a bit of water, and light pressure to remove the mortar from the top of the stones and also to smooth the mortar joints. This will pull the sand aggregate up from the joint, giving it a rougher look that fits in with the existing floor. Repeat as many times as necessary.
8. If the repair butts up to a wood structure, such as a stair riser, install a “soft joint.” Tape along the edge of the joint and the bottom of the wood. Squeeze the caulk into the joint. Use a bit of dish soap on the pad of an index finger and drag it along the caulk to smooth it out. Remove the tape, let it dry, and paint the caulk.
9. After the repair cures (around 28 days), apply a masonry sealer to the floor to protect it and give the floor some pop and shine.

Resources

Mark makes repairs to a 1960s flagstone entryway to ensure it’s safe and long-lasting. To address the
loose stone at the top of the basement stairs, Mark recommends gently removing any loose stone pieces and mortar with your hands.

Follow up by using a chisel and hammer to break away the old mortar to free the larger flagstone pieces. Use a masonry brush to clear any dirt or debris. For indoor masonry projects Mark recommends using a Type S mortar premix that only requires adding water.

For smaller repair jobs, mortar batches can be mixed in a rubber mixing tub in small quantities as needed. After applying a bed of mortar using a trowel, add construction adhesive to the bottom side of the stone before setting it in place. The adhesive will strengthen the bond as the mortar sets.

To address gaps between flagstone floors and stair risers, use silicone caulking. Mark recommends dipping your finger in blue dish liquid before smoothing out the caulk seam. This tip will help create a seamless finish.

Materials

• Concrete bonding agent
• Mortar mix
• Water
• Painter’s tape
• Construction adhesive
• Paintable caulk
• Masonry sealer
• Blue dish liquid

Tools