CAUSE & ORIGIN INVESTIGATIONS: MASONRY CHIMNEY FAILURES
https://sites.google.com/site/metropolitanforensics/cause-origin-investigations-masonry-chimney-failures
We inspected many failed masonry chimneys this past winter. This blog briefly reports some of the results of the cause & origin investigations.
Photo 1: Failed masonry chimney. Note the TV antenna attached to the chimney. The antenna contributed to the tortional twisting of the mortar joints and fracturing of several bricks, leading to the chimney failure in just few years. TV antennnas should not be mounted on chimneys.
Masonry chimneys are structures which provide ventilation for hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. A flue liner is a secondary barrier in a chimney that protects the masonry from the acidic products of combustion and helps prevent flue gas from entering the house.
Unfortunately chimneys are the least-inspected and least-maintained parts of the home. Regular chimney maintenance is essential to prevent damage, deterioration and future high-cost chimney repairs. Furthermore, improper flashings, incorrect/missing sealant or worn/damaged flashing around the chimneys are common causes for roof leak. The flashing of the chimney refers to the overlapping layers of metal (e.g., aluminum, copper or galvanized steel) sheets that safeguard against water where the roof and chimney meet. Some of the flashing should be located underneath of the roof shingles, and should travel up the sides of the chimney to provide seamless protection for this vulnerable area. This is not always done, leading to roof and chimney damage.
The most common problem we observed was water penetration into the chimney structure. During the cold winter months, the masonry materials deteriorate when exposed to freeze/thaw cycles. During these cycles, moisture that has penetrated the chimney freezes and expands, causing damage to the individual chimney components: mortar, bricks, concrete blocks, concrete crown, etc.
Water penetration can cause interior and exterior damage to a home and masonry chimney including:
• Spalling, pitting or efflorescence on the brick surface
• Cracking or crumbling of the cement blocks
• Rusted damper assemblies and fireplace doors
• Deteriorated metal or masonry firebox assemblies
• Rotting adjacent wood and damaged wall coverings
• Water stained or damaged walls and ceiling
• Clogged clean out port
• Stained chimney exterior
• Deteriorated exterior mortar
• Cracked or deteriorated flue lining system
• Leaning or collapsed chimney structure
• Chimney settlement
PHOTO 2: Heavily deteriorated chimney crown. Note the lack of rain cap, the deteriorated mortar joints and the organic growth inside and on the exterior of the chimney.
Why is there water penetration inside the chimney structure? The simplest explanation we can give is that the chimneys are not properly designed, constructed and/or maintained. Very rarely have we seen a chimney that is properly constructed. By far the most deficient area is the chimney crown (or chimney cover as some people call it) and the flashing around the chimney.
Most of the time the chimney’s crown is incorrectly constructed using the wrong concrete thickness or is flat. At other times we observed that the chimney had no rain cap. The lack of rain cap and/or a flat crown, in combination with lack of maintenance, allows water to enter the chimney from the top and cause water damage due to the freeze thaw cycles. This is a slow deterioration process and it starts when the chimney is built.
PHOTO 3: Heavily deteriorated chimney crown and chimney structure. Note the lack of rain cap, the deteriorated mortar joints and the black stains.
The chimney cover ideally is designed to protect the chimney from the rain and to shed rain water away from the chimney by tapering it and extending its drip line to at least 2 inches beyond the side of the masonry surface (the drip overhang); a drip groove is also recommended to shed water past the plane of the four chimney walls. The proper chimney cover should be constructed of Portland cement-based mixture and cast or formed with a downward slope so it directs the water away from the flue to the edge of the cover.
When water/moisture enters the chimney it will freeze and expand during the winter months, damaging the brick, cement block, mortar, stucco and perhaps the flue liner. Freeze-thaw damage cycles take many years to develop, are a long-term occurrence and they are not sudden or accidental events.
PHOTO 4: Spalled brick pieces that had been coated with stucco. The brick spalled and fell off the chimney along with the stucco.
Spalling is when the face of the brick breaks apart. The reason for the brick’s deterioration can be a result of many different things, but more often than not, it is the result of water freezing and thawing internally, which weakens the brick. Another reason is poorly made mortar (stronger than the brick). We often see spalling in bricks that have been coated with paint, stucco, etc. Coating the brick can lead to accumulation of salts beneath the brick surface (sub surface efflorescence) that can cause flaking of the brick.
Metropolitan Engineering, Consulting & Forensics (MECF)
Providing Competent, Expert and Objective Investigative Engineering and Consulting Services
We know you need to process damage claims quickly and knowing the facts is now faster than ever – within 24 hours of site visit. Our Pegasos Forensic Investigation Services (PFIS) feature:
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P.O. Box 520
Tenafly, NJ 07670-0520
Tel.: (973) 897-8162
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E-mail: metroforensics@gmail.com
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