Masonry Clay Flue Tile Defects
Masonry clay flue tiles meet a harsh environment inside the chimney. Corrosive condensation, moisture, chimney fires, and other conditions may damage a flue tile. In certain circumstances, a clay flue tile can last for decades, provided they are maintained and the homeowner operates the appliance or burns responsibly.

Latent Defects are defects found within the system from improper and sometimes creative use of material that stray from building codes or the manufacturer's installation instructions. This deviation from the codes or installation instructions creates various issues within an installation.

Wear and Tear is the natural aging process where material breaks down over time. Wear and tear can also include how an appliance is operated. If it is too hot, it decreases the life of the appliance, chimney, and connector pipe. If the temperatures are too low, it can create a tar-like creosote and increase the likelihood of a Sudden Occurrence (or condensation with gas/oil). Another factor is maintenance or lack of maintenance. Wear and tear can sometimes overlap with other categories.

Moisture and Condensation damage occur when water enters the chimney interior due to a missing cap, leaking crown, cracks in the brick structure, freeze-thaw breaks in the bed or head joints, and a poor choice of brick, causing excess water absorption. Another source of water in a chimney can come from condensation. This condensation occurs when the flue gas temperature falls below the dew point. Because of the water percentage in natural gas and liquid propane, the flue gases may condense in masonry chimneys, especially those located along the home's exterior.
The next fuel to condense is wood. When the warm gases reach the masonry flue liners, they, too, cool off. The moisture is included with the other byproducts of wood burning – black creosote, watery or tarlike soot.
The last fuel, oil, will also condense on the masonry walls. Due to the higher efficiencies that oil appliances can now operate, they too will condense and, with their acidic nature, can destroy masonry clay flue tiles.

A Sudden Occurrence is a sudden event that causes damage. It can be a chimney fire, a sudden weather-related incident(s) such as a tornado, strong wind, or a seismic event. It has to be out of the ordinary of daily operations.
A Sudden Occurrence, the last Pathway, includes damage seen from a direct and sudden event. Indirect manners can apply to areas where mine subsidence has occurred (where mining was performed). Of the Pathways, this last defect(s) will usually become an insurable loss. The other three defect categories – Latent Defect, Wear & Tear, and Moisture are generally not insurable losses since insurance contracts (policies) do not include them.

I’ve been involved in the chimney industry since the late ‘70s when my wife and I started our chimney sweeping business. Anyone who was a sweep during this time enjoyed a business that boomed during the fall and winter, then fell off in the spring and summer. How times have changed. In these early days, there were no criteria for chimney inspections. Chimney sweeps swept the chimney, maybe noted some issues to the homeowner about the soot level,and left. Litigation and insurance companies started to change the industry and were the basis for developing the industry’s Standard of Care. 
Taking the NFPA 211 Annex and placing it into installation type.
One day, at the turn of the century, as I sat on my deck relaxing, my mind wandered back to the year 1998 when a bunch of guys and I drafted the Levels of Inspections, Degrees of Access, and the list of inspection items in Chapters 14 & 15 and in the NFPA 211 Annex. As I thought about how it would be incorporated into a chimney technician’s inspection, I realized it would be difficult for the technician to try to hit all the inspection items from memory. Additionally, some items would apply to one type of installation, but not all. Today, 25 years later, some chimney technicians are still missing inspection items from NFPA 211. It’s almost as if our industry Standard of Care slipped through our fingers. Is it because there are too many items for a technician to inspect? No, we've become lazy and pick and choose what we want. This led me to begin my 10,000 hours of creating what became the Flue and Hearth Notes™ inspection forms. 
Different Installation Types.
Forty years ago, before NFPA 211’s Inspection criteria, an inspection form was created with a fireplace and a handful of inspection items to check. It was in triplicate form, and chimney sweeps used it for all types of installations. It was used for all chimneys. However, a fireplace inspection differs dramatically from a chimney serving a gas water heater and an oil boiler venting into one flue. Unfortunately, some chimney sweeps and technicians still use these forms.  Twenty years ago, I envisioned building a comprehensive inspection form Based on NFPA 211 but for specific applications such as a Masonry Fireplace, a Prefabricated Fireplace, a Masonry Thimble Chimney Serving an Appliance(s), and a Prefabricated Chimney Serving an Appliance(s).  Although these installations all have chimneys, each chimney vents a different type of heating unit or fireplace. In addition, the fuels can differ: LP gas, natural gas, oil, coal, wood, and pellets.
No installations are the same, but you will see the same types of defects.
Every installation is unique, but the types of defects are the same across the board. For instance, defects can range from vertical and horizontal cracks, protruding mortar joints, stacked liners, and misaligned liners to missing chimney liners.
Start creating a Unity track: Defining what’s important.
One of my all-time favorite stories is one Tom Grandy shared about a trip to the dentist. As with any dental visit, almost everyone gets the lecture about how to floss twice a day, and we are given the same demonstration of how to floss each time we brush. One day, after a lecture on flossing, Tom shared what we all feel, and the dentists regularly hear. “I hate to floss!” I suppose that day, the dentist had heard it for the umpteenth time, and he was ready. He responded, “OK, just do the teeth you want to keep!” This has similarities to our industry. A technician can’t just pick and choose what they want to search for (the insurable cracked flue liner). All inspection items must be investigated (NFPA 211, Chapters 14, 15, and the Annex). I felt pulling all this together would create unity on chimney inspections in our industry since it didn’t seem to be happening.
The start of the Flue and Hearth Notes™ (10,000 hours) of form building and why and how they are built.
I began with the vision of a unified form. I grouped inspection items with installation types. I further included an area for defects related to specific areas, such as a chimney liner. I grouped inspection items per area where they were found in the chimney or fireplace. I included information on appliances. I had professionally created drawings and pulled everything into multiple inspection report forms. Recently, I added more forms to the offering and broke them down by fuels. We now have eight form types: Masonry Fireplace, Masonry Fireplace with a Hearth Stove, Masonry Fireplace with an Insert, Masonry Thimble Chimney Serving a Solid Fuel Appliance, Masonry Thimble Chimney Serving a Liquid Fuel Appliance(s), Prefabricated Chimney Serving a Solid Fuel Appliance, Prefabricated Chimney Serving a Liquid Fuel(s) Appliance, and Prefabricated Fireplace and Chimney. We have Level I and Level II forms for each installation type. That’s 16 forms in total. But then, we went a step further.

Terra cotta flue tiles have been used for almost a century as an accepted liner for masonry chimneys. A brand-new flue may look like the photo shown on the right. The tile is new; it should not be broken (or, in this case, have a cutout view). 
 As the chimney is being built, flue tiles stack on each other and are mortared together with a joint. In the past, masons often used mortar such as type "S" or type "N" mortar, the same mortar they used to lay the brickwork. These mortars can erode, leading to open mortar joints and shifting flue tiles. Today, codes require a non-water-soluble refractory cement that withstands the onslaught of moisture. This creates longevity for your masonry flue. 
Equally important is a smooth interior mortar joint (specified by codes). The picture on the right is an example of a brand-new ideal joint. Mortar that protrudes into the flue can hinder flue gases and smoke. This may affect the way the fireplace burns. A smooth joint is an optimal joint.
Many other types of damage can happen to a masonry flue. To ensure your flue is in an operational-ready condition, ask the chimney sweep to continuously scan your chimney with a Chim-Scan® Internal Video Inspection System each year your chimney is cleaned.  Catching defects early and making repairs can preserve your investment in your fireplace, chimney, and home. 
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