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Unlined Masonry Chimney Repair

In the chimney diagram above, the orange colored terra cotta flue tiles are clearly displayed lining the entire chimney beginning at the smoke chamber and terminating at the very top of the chimney.

In the chimney diagram above, the orange colored terra cotta flue tiles are clearly displayed lining the entire chimney beginning at the smoke chamber and terminating at the very top of the chimney.

If you have a masonry chimney, its structure is made up of several layers (or courses) of bricks stacked one on top of another and glued together with mortar by a skilled mason… but what’s inside the chimney? What keeps all that heat, smoke, and carbon monoxide safely contained where it belongs until it escapes out the top of the chimney? Hopefully an inner liner of terra cotta flue tiles!

In addition to the chimney’s outer bricks, masonry chimneys should have an inner layer of protective terra cotta flue tiles that line the inside of your chimney from the very top, all the way down to your smoke chamber. Orange or yellow in color and usually square or rectangular in shape, these terra cotta flue tiles are a VERY important protective component of your masonry chimney!

If your chimney was built without this protective inner liner, you have what is called an “unlined chimney” and you need to read the rest of this article! Your chimney may be a hazard to your home and the lives of you and your family!

Looking straight down this chimney's terra cotta flue, you can see how each flue tile is about 1 foot tall, and sealed together with a mortar joint as they are stacked one on top of another.

Looking straight down this chimney’s terra cotta flue, you can see how each flue tile is about 1 foot tall, and sealed together with a mortar joint as they are stacked one on top of another.

Most people don’t realize that red bricks (the type of bricks most often used to build masonry chimneys) are actually a very poor insulating material. In other words, if hot smoke and gases were allowed to come in direct contact with the inside surface of your chimney’s brickwork, the red bricks could quickly allow this heat to travel through the bricks and be hot to the touch on the outside!

With most of the house removed, this rare view of a typical chimney's construction studs often come in direct contact with a chimney's outer red brick structure.

With most of the house removed, this rare view of a typical chimney’s construction studs often come in direct contact with a chimney’s outer red brick structure.

Because red bricks are good conductors of heat, in and of themselves, they do not provide a very safe barrier between your fire’s heat and the combustible wood 2X4’s that make up the structure of your home! Quite often, older homes were built with combustible wood framing in direct contact with the chimney’s brickwork, so it is imperative that your fire’s heat not be allowed to transfer through the chimney walls and catch your home on fire!

This picture clearly shows the different layers of masonry on a modern chimney: The outer most layer made up of red brick, and the inner most layer constructed of terra cotta flue tiles.

This picture clearly shows the different layers of masonry on a modern chimney: The outer most layer made up of red brick, and the inner most layer constructed of terra cotta flue tiles.

It is for this reason that most modern masonry chimneys are actually made up of 2-3 layers of different materials! The outer 1-2 layers are made up of red brick, and the innermost layer is a different type of clay material called terra cotta flue tiles. These flue tiles are usually 1-2 feet tall, and stacked one on top of another with a layer of mortar joining each flue tile to the next creating a continuous, air tight passageway designed to contain and convey the byproducts of combustion up and out of the home safely.

How important is this terra cotta lining?

Due to safety concerns, building codes have required that masonry chimneys be built with a flue liner since the early 1930’s.

In the 1940’s, and once again in the 1980’s, the National Bureau of Standards did extensive testing on masonry chimneys for durability and safety. These tests involved both lined (using terra cotta flue tiles) and unlined chimneys. The results of this testing was very clear:

Looking straight down this unlined chimney, you can clearly see how badly the mortar is deteriorated due to acidic flue gasses.

Looking straight down this unlined chimney, you can clearly see how badly the mortar is deteriorated due to acidic flue gasses.

1. Unlined chimneys were found to be very unsafe! Common red brick (what most typically makes up the outer shell of most masonry chimneys) readily allowed the smoke’s heat to transfer through the brickwork and onto adjacent 2X4’s (making up the roof and walls of the home) igniting them after only three and a half hours of testing! In fact, the unlined chimney performed so poorly that they abandoned testing of unlined chimneys altogether!

a) In addition to a major fire hazard, it was determined that if acidic flue gases (smoke) were allowed to contact and penetrate the inside surfaces of the chimney’s red brickwork (outer structure), it would equate to a reduction in the usable life of the chimney due to mortar deterioration. The glue (mortar) that holds the chimney’s brick structure was literally being eroded from the inside out due to the fact that wood smoke is acidic in nature!

With no orange colored terra cotta flue tile poking out of the top of this chimney, it is easy to determine that this chimney is unlined.

With no orange colored terra cotta flue tile poking out of the top of this chimney, it is easy to determine that this chimney is unlined.

With no terra cotta flue tile poking out of the top of this chimney, it is easy to determine that this chimney is unlined.If your chimney s somewhat older, and does not have a terra cotta clay tile flue liner, your chimney is what we call an “unlined chimney”, and it is a serious potential safety hazard should you choose to use it. We cannot stress enough… if your masonry chimney is unlined, DO NOT BURN FIRES until it is repaired and safe for use.

In most cases, unlined chimneys can be made safe for use by having it relined by A to Z Chimney Sweep. Relining usually involves having a custom-made, fully insulated stainless steel liner from the very top of your chimney, all the way down to the very bottom of the chimney where the smoke chamber ends.

Continuing to burn fires in an unsafe chimney can be disastrous!

Continuing to burn fires in an unsafe chimney can be disastrous!

Once your chimney is relined, you can burn your fires with peace of mind knowing you did the smart and responsible thing by having it relined with the proper materials by a professional company!

 

One of the safest remedies for an unlined masonry chimney is a stainless steel chimney liner. Find out all the facts about this and other types of chimney repair by calling A to Z today!


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