How Should I Address the Cracks In My Chimney?

Doug is working on a 26-ft tall chimney with visible hairline cracks, as well as larger cracks that seem to follow the cinder block lines. He’s asking if painting the hairline cracks with elastomeric paint and then applying acrylic paint over the entire chimney after repairing the larger cracks would be a good solution. 

Question from Doug:
Would painting the hairline cracks with elastomeric paint, then paint the entire chimney with acrylic paint after repairing the other cracks be a viable option? Additionally, any tips on the best way to repair the cracks? The cracks up top appear to follow cinder block lines. The mortar between the flue tiles is in bad shape, but that is another project. The chimney is 26 ft tall and 73" x 32" wide.

Cracks On Chimney
Cracks On Chimney 2

Answer:
Hi Doug, thank you for your question and the detailed photos, they really help! Here’s how I’d approach your situation:

Painting Hairline Cracks with Elastomeric Paint

While elastomeric paint can work on hairline cracks, caulking these cracks would be a much better option. Caulking provides a more targeted seal, effectively preventing water intrusion and ensuring a longer-lasting repair.

Additionally, caulking allows you to precisely address each crack, giving you control over the repair process before painting. If you do plan on using Elastomeric paint, here are a few things to keep in mind:

  • It’s most effective on cracks that are truly hairline in size (less than 1/16").

  • Before applying elastomeric paint, ensure the surface is clean, dry, and free from loose debris for the best adhesion.

Once the elastomeric paint is applied and cured, coating the entire chimney with acrylic paint is a good move. Acrylic paint provides an additional weather-resistant layer and helps maintain a uniform appearance.

Repairing Larger Cracks

For the more significant cracks, particularly those that seem to follow the cinder block lines, here’s a step-by-step approach:

  1. Clean the Cracks: Use a wire brush to remove any loose debris or crumbling material.

  2. Fill the Cracks: For cracks wider than 1/16", use a high-quality masonry or stucco patching compound or a quality exterior-rated caulking (avoid silicone). Apply it with a trowel, putty knife, or your finger, working it firmly into the cracks.

  3. Tool the Surface: Smooth the repair area with a trowel or float to match the existing texture the best you can.

  4. Prime the Area: After the patch has fully cured, apply a masonry primer (if unpainted cement based stucco) over the entire surface of the chimney to ensure proper adhesion of the top coat of paint.

Addressing Larger Patches

In areas where larger chunks of stucco material are missing, like the larger patch visible in the second photo, you’ll need to:

  1. Clean the Area: Remove any loose debris or deteriorated stucco to create a clean surface.

  2. Apply a Base Coat: Use a stucco base coat material to fill the area, ensuring it’s packed tightly and smoothed to a uniform surface.

  3. Add a Finish Coat: After the base coat has set, apply a finish coat of stucco material to match the existing texture. If you prefer, the base coat material can also be used as the finish coat in smaller patches.

  4. Blend the Edges: Carefully feather the edges of the patch into the surrounding surface to minimize visibility.

Addressing the Chimney’s Top Section

Cracks following the grout lines of cinder blocks are typical and usually indicate minor settling or movement. Large cracks, however, are what you want to watch out for.

Additional Considerations

  • Flue Tile Mortar: Since you mentioned the mortar between the flue tiles is in bad shape, it’s important to address this eventually. Deteriorated mortar can compromise the chimney’s structure and lead to water intrusion issues.

  • Height Safety: At 26 feet tall, working on the chimney will require proper scaffolding to be set up or hiring it out to a professional, for safety reasons.

By addressing the cracks systematically and combining the repairs with caulking or elastomeric and acrylic paint, you’ll protect the chimney and improve its appearance. Let me know if you need further clarification or help!

About the author

The Stucco Guy

My name is Ryan and I have been a licensed stucco contractor for many years and I feel that there is a huge "knowledge gap" when it comes to stucco, in particular. I hope you find the information here useful, and if you have a question for me fill out this Q & A form, so I can answer those questions better. Thanks for stopping by!

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