The crown is the topmost part of the chimney. It consists of a mortar cap that is designed to protect the top course of bricks from moisture incursion. The crown is also made to be covered by the final chimney cap, which will then keep moisture and debris out of your chimney. If damaged you should book chimney masonry repair as soon as possible.
1. Masonry Debris
Debris from the deteriorating crown can tumble down the chimney and collect in the firebox or on the hearth. As the crown deteriorates the mortar that it is made of, along with chips from collateral damage to the top courses of bricks and flue tiles, can lead to mortar and brick debris falling down the chimney to collect in the firebox.
2. Hairline Cracks
Damages often first appear as hairline cracks on the crowns mortar. You may not be able to see the cracks from the ground, which is why annual chimney inspections are important. If caught early enough, an epoxy sealant can be injected into the cracks to fix the damage. Extensive cracking or large cracks can't be as easily repaired, so you will likely need a new chimney.
3. Rusty Damper
A damaged crown will allow moisture into the fireplace, which can lead to rust on metal components like the flue damper. If your damper is covered in rusty residue, or if it is difficult to move it due to rust and corrosion, then you know moisture is making its way in. Check the crown first, as crown damage is the most likely source of this moisture.
4. Spalling Damages
The bricks on the chimney immediately below the crown can also begin to show signs of moisture damage. As the crown deteriorates, moisture finds its way into the mortar and eventually into the tiers of bricks just beneath the crown. Freeze and thaw cycles can cause moisture in the bricks to expand, which leads to spalling. A spall is a chip that breaks off the face of a brick, and it will lead to further deterioration.
5. Cap Issues
The chimney cap sits atop the crown, but it may not be sitting properly or securely if the crown is damaged. If your cap looks crooked or loose from the ground, then it needs to be inspected. In some cases it can simply be put back into place, as wind or even animals may have knocked it loose. In other instances it may be indicative of crown damage that no longer allows the cap to be seated properly.
Contact a masonry chimney repair service if you suspect issues with your chimney crown.