The crown is cracked or the brick is crumbling

What has probably happened

• The crown was poured thin or flush with the brick, so it cracked and sheds water into the masonry instead of clear of it.
• Freeze and thaw — water gets into a hairline crack, freezes, and levers it open.
• Mortar joints have eroded and the stack is now porous.
• Spalling: saturated brick faces pop off after freezing.
• The whole stack has been taking on water for years because there was never a cap.

What the technician does

• Crown repaired, or recast properly with an overhang and a drip edge so water leaves the structure.
• Repointing where the mortar has gone, matched to the existing work.
• Spalled brick cut out and replaced.
• A cap fitted, which is what stops it recurring.
• Breathable water repellent applied where appropriate.
• A rebuild of the stack above the roofline where it has lost structural integrity — and a straight answer about whether it truly needs one.

Questions people ask

Repair or rebuild?

It depends how far down the damage goes. A cracked crown on a sound stack is a repair. A stack with failed joints and spalled brick through several courses is usually rebuilt above the roofline. A technician should be able to show you the difference on the photographs.

Can this wait until spring?

Freeze and thaw is exactly what makes it worse, so waiting through a winter is the expensive choice in cold regions. At minimum get it capped and covered before the freezes start.

Does the whole chimney need rebuilding?

Rarely. Most rebuilds are the portion above the roofline, which is the part exposed to weather on all sides.