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Failed Chimney Cap and Deteriorated Liner

Gas fired appliances exhaust contains acid. This is a sever problem when a chimney is on an outside wall where it is not kept warm by a surround house. In cold weather gas exhaust condenses on the cold surfaces of your chimney where it deposits acid on the flue liner and mortar joints. The acid will then over time eat the cement out of the mortar and dissolve the terracotta. If you do not have a chimney flue liner in place it is advised you inspect your chimney for damage. Below is a story from work at a house with an exterior chimney (1).

This project started when I found shards of mortar in the gutter around the chimney of a repeat client. A photo of the top of the chimney showed the presence of a failing patch (2).

During removal of the previous superficial patch the concrete chimney cap was found to be cracked. During removal of the cracked cap the surrounding brick crown at the top of the chimney started coming loose (3). It became evident the mortar was eroding from the inside out (4).

Since it was impossible to stop some debris from falling down into the chimney during demolition and cleaning I checked the HW heater vent connection to the chimney to make sure my work caused no problems below. I found the HW heater vent was rusting from the same acid exposure (5) and partially blocked by years of eroded sand and terra-cotta chips (6).

After removal of the damaged brick and top terra cotta liner (7) it was obvious the next terra cotta liner down had also been compromised (8). An evaluation of appliance draft requirements and the reasons for the damage necessitated installation of a B-vent (9) to get exhaust to the top of the chimney and stop continued damage to the masonry.

Exterior Chimney

1) Exterior Chimneys Need Liners

parging patch failure

2) Parging Patch Found In Gutters

Loose material at top of chimney

3) Removal of Loose Material

liner damage

4) Terra-cotta Liner

rusted HW flue brick

5) Rusted Hot Water Flue

Debris in wall

6) Eroded Debris Removed From Base of Chimney

Damaged Removed

7) Loose Brick and Top Flue Liner Removed

damaged flue liner

8) Flue Liner Beyond Repair

Repaired Cap

9) New Chimney Cap and B-Vent Liner

Please call (703.524.7595) or email ( for more information.
Located in Arlington, Virginia 22207 (by appointment only)