Flue Repair

What goes wrong with clay flues

A clay tile flue is a stack of square or rectangular sections joined by mortar. Each joint is a potential weak point. Common problems include:

• Gapped or open joints where mortar has eroded or was never fully packed during construction
• Vertical cracks from heat, especially when a cold flue heats quickly
• Chips and spalled sections from moisture and acidic condensation
• Displaced or missing pieces after a chimney fire, a lightning strike or settling

A damaged flue can let heat reach nearby wood framing, and let smoke and carbon monoxide move into gaps in the chimney. It's a part you can't see from inside the house, which is why it often goes unnoticed.

Damage doesn't always come from age. Clay liners in some older chimneys were installed with joints that were never fully filled, or with gaps where sections didn't sit tightly together. A camera inspection on a chimney that has never had problems can still show those construction gaps.

Clues that point to the flue

• Pieces of clay tile or mortar falling into the firebox or on the smoke shelf
• An inspection report noting cracked or gapped tiles
• A recent or suspected chimney fire (see signs of a chimney fire)
• Smoke or odors appearing in other rooms or upper floors while a fire is burning

These are clues, not a diagnosis. Our guide to what cracked flue tiles mean explains the possible causes.

How we assess it

Flue repair decisions depend on what a camera can show. We sweep the flue first so the footage shows tile and joints rather than soot. We then run a chimney camera through the flue where it allows, recording every section: crack direction and length, how wide joints are open, whether tiles are offset or missing, and whether the damage is concentrated or spread over the length.

We also note what the flue serves, its size relative to the appliance, and outside conditions such as the crown and cap. You receive the photos or footage and our findings before any repair is scheduled. If a section can't be seen clearly, we'll tell you.

HeatShield resurfacing and joint repair

HeatShield is a manufacturer-made system for repairing clay tile flues in place. The manufacturer, Saver Systems, describes it as a way to repair cracked, gapped and deteriorated clay flue tiles while keeping the original chimney structure. The materials are high-temperature refractory sealants applied inside the flue.

Broadly, there are two approaches:

• Joint repair fills open or eroded mortar joints between tiles.
• Resurfacing coats the inside of the flue to cover cracks, small voids and spalled areas, forming a new interior surface.

We offer both joint repair and full resurfacing. The work follows the manufacturer's instructions, and after it is done we run a camera inspection through the flue to document the result.

Resurface or reline?

Resurfacing largely keeps the existing flue size, which can be an advantage for fireplaces where a smaller liner would hurt draft. It doesn't correct a flue that's the wrong size for the appliance. The full comparison is in our guide to flue resurfacing vs. a new liner.

After a chimney fire

A chimney fire can crack tiles along much of the flue. If you suspect one, the flue should be inspected before the fireplace or stove is used again. Whether resurfacing or relining follows depends on the extent of damage the camera shows. See chimney fire damage inspection and what to do after a chimney fire.

Before a flue repair

A few things usually happen before any flue repair can be planned or done:

• We sweep the flue so the camera can show tile and joints rather than buildup. Glazed creosote may need to be treated first.
• Water entry is checked. If the cap or crown is letting water in, that's addressed too, or the new surface will face the same conditions that damaged the old one.
• The flue's use is confirmed. Whether it serves a wood fireplace, a stove, or a gas or oil appliance affects whether resurfacing or a new liner is the right fit.
• The appliance is out of use during the work and for any curing time the manufacturer requires afterward.

After the repair, we photograph the finished work, and footage of the finished flue gives you a record you can compare at future inspections.

Limits and what affects the scope

• The extent and spread of damage over the flue's length
• Flue height and shape, and any offsets
• Whether creosote buildup has to be removed first
• What the flue serves and whether its size suits the appliance
• Repairs inside the flue don't fix water entry through the crown or cap that may have caused the damage

Next step

If an inspection noted cracked or gapped tiles, or you've found pieces of tile in the fireplace, request a flue assessment. If you have earlier inspection footage or photos, mention it. A team member will contact you to confirm a time.

Request a flue assessment

Questions homeowners ask

Sources

1. Saver Systems: HeatShield chimney flue repair