Chimney repairs, explained

St. Louis winters swing above and below freezing again and again. Water soaks into brick and mortar, freezes, expands and pushes them apart. That is why so much chimney repair is about keeping water out.

Tuckpointing

Worn mortar joints are ground out and refilled with fresh mortar. Done before bricks loosen, it is one of the best-value repairs. On older homes, ask for a soft lime-based mortar that matches the original. Hard modern mortar can be stronger than old brick, and the brick then cracks instead of the joint.

Crown

The crown is the concrete or mortar top on the brick that sheds rain. Small cracks can be sealed. A badly cracked or flat crown is often rebuilt with an overhang so water drips clear of the brick below.

Cap

A metal cap over the flue keeps out rain, birds, raccoons and squirrels, and stops embers from landing on the roof. It is one of the cheaper fixes and is often added during other work.

Flashing

Metal pieces seal the gap where the chimney meets the roof. A ceiling or wall stain near the chimney often points here. Flashing work may involve a roofer, so ask who handles it.

Liner

The liner is the inside of the flue. Some older homes have clay tile liners that crack, or no liner at all. A stainless steel liner is a common fix and costs more than outside repairs. A furnace or water heater that vents into the chimney can also need a liner sized for it.

Rebuilds

When bricks above the roofline are loose or leaning, part of the chimney may be taken down and rebuilt. Unused chimneys can sometimes be taken down below the roofline and roofed over instead.

Ask every contractor

• Photos of the problem from the top and inside the flue
• Whether mortar will match old soft brick
• Who handles flashing and roof patching
• What the warranty covers
• Whether a permit is needed in your town

Water repellent

After repairs, some contractors offer a breathable water repellent for the brick. It should let moisture out, not trap it. Ask what product they use and how long it lasts.