Problem-Solving: Crowns, Mortar Joints and Flashing
The chimney crown( also referred to as the“ chimney wash”) is the top portion of a masonry chimney. It covers and seals the top of the chimney from the flue liner to the chimney edge. The crown should provide a downward slope that will direct the water from the flue to the edge of the wash. When there is an overhanging drip edge, by directing the run-off from the crown away from the chimney, it helps prevent erosion of the brick and mortar in the chimney’ s vertical surfaces.
Most masonry chimneys are built with an inadequate crown constructed from common mortar mix that is designed for years of weather abuse without cracking, chipping or deteriorating. A proper chimney crown should be constructed of a Portland cement-based mixture and cast or formed so it provides an overhang projecting beyond all sides of the chimney by a minimum of two inches. The flue liner tile should also project above the crown a minimum of two inches.
Deteriorated mortar joints on the chimneys exterior are entry spots for water. Proper mortar joints have no gaps or missing mortar and are shaped in a way that directs water out of the joint. When mortar deteriorates from exposure to weather, it becomes much more absorbent. A common repair for deteriorated mortar joints is called repointing. In this process, the existing mortar joint is cut to an appropriate depth and the joint is repacked with new mortar. The joint is then cut to form a concave surface that will direct water out of the joint. A good repointing job, using proper materials, will give the chimney a much longer life span and often will enhance its appearance.
Flashing is the seal between the roofing material and the chimney. Flashing prevents rainwater or snow melt from running down the chimney into living spaces where it can damage ceilings and walls and cause rot in rafters. The flashing is the expansion joint between two dissimilar materials. It is designed to allow both the roof and the chimney to expand and contract at their own rates without breaking the waterproof seal in either area.
Damaging Results of Water PenetrationWaterproofing and Leak Prevention
If a chimney is located on the low side of the roof where water run-off is directed against the chimney, the installation of a cricket will afford additional protection against water leaking into the community. A cricket is a water deflector that serves to direct rainwater away from the chimney. Crickets are recommended on chimneys more than 30-inches wide and are especially important on steep roofs.
Most masonry materials are porous and will absorb large amounts of water. Common brick is like a sponge, absorbing water and wicking moisture to the chimney interior. Defective mortar joints or the use of improper mortar or brick can greatly increase the tendency to absorb and convey water to the interior of the masonry chimney.
Several products have been developed specifically for use as waterproofing agents on masonry chimneys. These formulas are 100 percent vapor permeable, which means that they allow the chimney to breathe. Therefore, water that has penetrated and the vapors produced when the chimney dries out or the water vapors produced during use are allowed to escape, while the waterproofing agent prevents water from entering from the outside. These products usually have a five- to 10-year warranty. Paint or clear sealers should never be used as a waterproofing agent because they will trap water vapors and moisture inside the chimney, causing further deterioration.
Waterproofing is a preventive measure. When damage or deterioration( gaps, voids, cracks, missing mortar, etc.) already exists in a masonry structure, the chimney should be repaired before the waterproofing agent is applied. The chimney exterior may also need to be cleaned before the waterproofing material is applied.
Ashley Eldridge is Director of Education at The Chimney Safety Institute of America( CSIA), a nonprofit organization formed in 1983, is the industry leader in chimney and dryer vent maintenance education.
Damaging Results of Water Penetration
Water penetration can cause interior and exterior damage to a masonry chimney and, by extension, the community itself including:
• Rusted damper assemblies
• Deteriorated metal or masonry firebox assemblies
• Rusted fireplace accessories and glass doors
• Rotting adjacent wood and ruined wall coverings
• Water stained walls and ceilings
• Clogged clean-out area
• Deteriorated central heating system
• Stained chimney exterior
• Decayed exterior mortar
• Cracked or deteriorated flue lining system
• Collapsed hearth support
• Tilted or collapsed chimney structure
• Chimney settlement
26 March / April 2017 | www. saaaonline. org