​A leaky chimney can cause deterioration and unpleasantness. Moisture can cause many problems to the chimney and flue. It can also damage drywall, ceilings, and cause your fireplace to smell. An open chimney top leaves the chimney vulnerable. This big open area resembles a giant rain gauge but is much more significant.
An open chimney lets in moisture, such as rain, sleet, snow, debris, and animals, which causes deterioration and an unpleasant smell. A quality rain cap works like a big umbrella, directing rain away from the flue opening. A chimney cap with a screen is the best option, as the screen will deter animals from wanting to nest in your chimney.
A chimney crown (or wash) is a barrier that prevents moisture from entering the cavity between the flue tiles and the interior of the brick (or stone). It starts at a gap near the flue tile and extends to the exterior brick, often with an overhang and a drip edge. Cracks in the chimney crown allow moisture into the chimney, and the cracks can expand when the moisture is frozen, accelerating the damage. Most cracks in a chimney crown can be repaired, but if severe, the crown can be replaced.
Chimney flashing and counterflashing is a metal material that forms a moisture barrier between the chimney and the roofing material. Defective or improperly installed chimney flashing can let water into the chimney and the home since It tends to follow the chimney into an attic or enter rooms below the chimney, damaging ceilings, drywall, and other materials. Repairing or replacing the flashing will direct moisture away from the gap between the chimney and the home's structure.
Moisture can wash out the mortar joints holding the flue tiles together. The flue tiles are the first line of defense against combustion products. If the mortar is missing, the tiles can shift, or at the very least, they will leave an opening in the flue. Moisture can also cause flaking of the flue tile and bring creosote and mineral salts through the mortar to the chimney’s exterior, leaving dark creosote and (white) efflorescence stains.
When moisture has caused flue defects, several solutions can be explored. If the mortar joints are missing, relining the chimney is one option, or resurfacing the flue may be necessary (the flue tiles must be intact and aligned). A chimney technician can use stain removal cleaners to remove stains on the exterior. Another option is waterproofing the chimney’s exterior if the moisture penetrates the brick-and-mortar (or stone) exterior.
As more moisture travels down the chimney and into the flue, damage can occur, such as eroded mortar joints in the flue, smoke chamber, and firebox, particularly the back wall. It can rust a fireplace damper, glass door, and screens. This moisture will continue to break down the fireplace and damper while creating an unpleasant smell from the wet soot and debris, particularly in the spring and summer. The fireplace can be repaired and the damper replaced, but the moisture must first be stopped. Cleaning the flue and smoke chamber may help, but often, the soot is already soaked into the masonry, and it is impossible to remove all of it.
The best way to prevent moisture problems is to ensure that leaks are taken care of promptly to avoid further erosion problems. Keeping moisture out of the chimney will prolong its life and reduce annoying stains and odors. By spending a little now, costly future repairs can be avoided. Take heart; if there is damage from moisture, it can be repaired by a chimney professional so you can continue to enjoy your fireplace.
​