How to Make Common Chimney Repairs

At a job site, mason Mark McCullough talks about chimney repairs. Mark shows Kevin O’Connor what to look for when planning out a repair before the pair roll up their sleeves and get to work.

Chimneys have tough lives. They live outdoors, and they’re always exposed to the elements. After a while, their joints and bricks can begin to fail, allowing them to take on water in inclement weather. But homeowners can avoid further damage by recognizing common chimney issues and repairing them before they go too far.

Common Chimney Problems

There are a few ways that chimneys can fail, but some are much more common than others. The following are some of the most common chimney problems that homeowners should look out for.

• Mechanical fasteners: Screws that hold chimney caps in place aren’t ideal. They create penetrations through the concrete where water can collect and freeze. Instead of fasteners, homeowners should consider caulking their caps in place with silicone to allow for expansion and contraction.
• Broken bonds between mortar and brick: Check for places where the mortar is beginning to separate from the edges of the bricks. These spaces are ideal for water infiltration.
• Loose aggregate: When brick pointing is complete, the joint is smooth, sealing water out. If it’s no longer smooth and dragging a finger across the mortar joint releases sand and small stones, the mortar joint likely needs replacing.
• Flashing damage: Be sure to check the flashing around the base of the chimney to ensure it’s in good shape and will keep water out of the home.
• Poor draft: If the chimney doesn’t pull smoke out of the home, it may have a bad draft due to design. In this case, it may be necessary to call a pro in to heighten the chimney properly and safely.

How to Make Common Chimney Repairs

Note: Working on roofs can be very dangerous. If the roof is flat, consider cordoning off the edges with a safety barrier. If the roof is sloped, be sure to wear a fall arrest harness tethered safely to an anchor point.

1. Start by assessing the damage for broken mortar and brick joints, chunks of mortar missing, or aggregate falling out of the mortar. These areas will need repair to make them water-tight again. Also, now is the time to don safety glasses, work gloves, and a respirator for safety’s sake.
2. Attach the HEPA filter to the grinder. Working slowly, grind an inch or so of the existing mortar away from the horizontal joints, also known as bed joints. Work back and forth, carefully removing the mortar. Do not use the grinder on the vertical joints, or you could damage the existing brick. Use the masonry chisel and hammer to chip away at the vertical joints, also known as head joints. Again, be sure to wear safety glasses.
3. Use a masonry brush and water to clean the joints and wet the brick. The brick will absorb the water and prevent it from pulling the water out of the new mortar, allowing the chemical reaction to occur properly.
4. Mix the mortar mix with water in a bucket until it reaches an oatmeal-like consistency. Be sure to add water slowly to prevent the concrete from getting too soupy.
5. Scoop mortar mix onto a mason’s trowel and apply to the head joints, pushing it deep into the joint until the new mortar is pressed up against the old mortar, removing any gaps. Use the pointing trowel to press the mortar into the brick. Smooth the joints with the trowel.
6. Following a similar technique, scoop mortar onto the larger trowel and press it into the bed joints. Be sure to push it up to the existing mortar to take up any space. Smooth the joints with the trowel.
7. After a few days, wash the repair area with a masonry detergent before allowing it to dry. Spray the repair area with a waterproofing agent to prolong the life of the repair. Use a sprayer and start at the bottom of the chimney, working side to side to apply the waterproofing agent.

Resources

Mark & Kevin discuss common chimney problems and arm homeowners with the information they need to hire a licensed professional to carry out the repairs, including safety protocols.

They then work together to repoint the chimney by first grinding down the mortar joints. To do this, they use a grinder with a vacuum attachment and hand chisel and wear the proper safety equipment, including safety glasses and earplugs. They remove excess dust with a damp masonry brush, then use type-N mortar to fill the joints. For this process, they mix the type-N mortar to an oatmeal consistency, then use a finishing trowel and margin trowel to apply the mortar to the chimney.

Based on the age of the chimney he repointed (over 100 years old), after the mortar cures (cure times vary, check the label on the mortar), Mark will apply a waterproofing agent to the chimney. Mark suggests first cleaning the chimney exterior with a masonry detergent, then using a waterproofing agent by applying one coat to the chimney with a spray attachment. To apply the waterproofing agent, work your way side-to-side, beginning at the bottom of the chimney, then moving up the chimney to the top.

All products can be found at a local home center.

Materials

• Type N mortar mix
• Waterproofing agent
• Earplugs
• Masonry detergent

Tools