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