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The Sterling Chimney Sweep teamChimney cracks: which ones are serious?
A thin crack in mortar that is not growing can wait for a scheduled visit. Cracks that run in a stair-step or across, cracks in the crown, and any crack that widens or leaks need a look soon. Where the crack is and how it is changing tell you more than its length.
How do the common cracks compare?
| Where and how | What it often means | What to do |
|---|---|---|
| Thin crack in a mortar joint | Normal wear | Watch it, plan tuckpointing |
| Crumbling or missing mortar | Water can enter the joint | Book a repair visit |
| Stair-step crack across bricks and joints | Part of the chimney is moving | Call soon |
| Horizontal crack | Possible shifting or heat damage | Call soon |
| Crack across the crown | Rain has a path into the stack | Book a look |
| Gap where chimney meets the house wall | The stack may be pulling away | Call soon and keep clear |
Why do cracks keep coming back?
Water is usually the reason. It soaks into a crack, freezes and widens it, then thaws and drains in deeper. A patch that does not stop the water only delays the next crack. That is why a repair starts by finding where the water enters, whether at the crown, the flashing or the joints below.
What you can check safely
Use the ground, a phone camera and its zoom. Take a dated photo of each crack and compare it a few weeks later. Look at the brick faces for flaking and at the base for pieces that have fallen. Never climb or lean a ladder on the chimney.
- Check which direction a crack runs: straight, stair-step or across.
- Look for stains or damp patches under cracks.
- Look for cracks inside the house near the chimney.
When to stop and call
Stop and call: if a crack widens between photos, if bricks are loose or have fallen, if the chimney looks tilted, or if smoke comes into a room. Keep clear of the base until we have looked. Our chimney repair service covers tuckpointing, crown work and rebuilds. You can book a look in Newport or Mendota Heights.
Crack questions
Short answers first.
Is a crack in chimney mortar normal?
Thin cracks appear as mortar ages. They are worth watching, because water enters through them and freezing widens them over time.
How do I tell if a crack is growing?
Photograph it from the same spot with the date, then compare a few weeks later. If it looks wider or longer, call us.
Can I fill a chimney crack myself?
A surface patch can hide a crack without stopping the water. The repair has to reach into the joint, and that work happens on the roof, so leave it to us.
Do cracks inside the house mean the chimney is failing?
Not always. Settling can crack walls and plaster alone. A crack running along the chimney wall that keeps growing is worth a look.
Found a crack you are unsure about?
Describe where it is and which way it runs, and we will tell you how soon it needs a look.