We see them everywhere but rarely give them much thought. Yet, chimneys are an important safety feature of many homes, especially those that were built 50+ years ago.
Some exist only to vent harmful fumes from your water heater and furnace while others have fireboxes at the bottom for heating your home on a cold winter’s night.
What they all have in common is that they need maintenance and can wreak havoc on your home if problems are allowed to fester.
Chimney Design
Made of brick on the exterior, the interior can differ in material from chimney to chimney. Old systems can become obsolete.
New and simpler solutions come along and the manufacturers of old school parts either disappear or follow modern trends. Don’t be surprised if a mechanical portion of your chimney is no longer considered worth replacing.
Chimneys Are Machines
While an old technology, chimneys are carefully designed machines. Each portion is built for a specific purpose with the design being improved over centuries of trial and error. Within every chimney you will find the following:
- Firebox (if a fireplace is included)
- Throat
- Damper
- Smoke shelf
- Flue
- Flue lining
- Crown
- Cap
- Flashing
Each of these elements aids in drawing air up, through and out of your home. Failures in this machine, like any other machine, lead to unpleasant and potentially dangerous results.
Materials
We all know that the majority of chimneys are made of brick, but that isn’t the whole story. Many other materials are used in the building of chimney systems with new materials being developed all the time.
Bricks
Chimney bricks come in a variety of types with different strengths and weaknesses. This table should help you decide which type you should use to build or repair your chimney[1].
| Type | Appearance | Strength | High Temp | Surface | Coating Needed | Water Resistance |
| Common Burnt Clay | Red | Common | Common | Rough | Plastering | Common |
| Sand Lime | Grey | Load Bearing | Common | Smooth | None | Common |
| Engineering | Varied | Load Bearing | High | Smooth | No but can be painted | High |
| Concrete | Varied | Load Bearing | No | Rough | Sealant | Common |
| Fire Ash Clay(Fire Brick) | Pale Color | Low | Extreme | Rough | No | None |
Liners
Your flue will often be formed of fired clay but that isn’t enough for withstanding the constant heat, soot and creosote that your flue must endure.
Linings are used to resist these elements and to make maintenance easier and less prone to damaging the flue.
Common liner materials are:
- Clay tile – Found in older homes this material can crack if not carefully maintained.
- Metal – The corrosion resistant qualities and flexibility in installation make these the popular choice in modern chimneys and in flue repair.
- Cast-In-Place – Highly heat resistant and leaving behind a seamless and smooth surface this material is also quite popular for flue repairs. Not all chimneys can use this system.
Mortar
The mortar used in building chimneys is not the same as the type used in general construction. Chimney mortar is rated for withstanding high temperatures. Make sure you use the proper mortar in your chimney repairs.
Maintenance
All chimneys, regardless of design, require maintenance to ensure proper operation. Some maintenance should be done on an annual basis while other preventative steps need only periodic attention.
Annual
Following an annual maintenance program for your chimney will prevent greater expenses down the road in the form of repairs.
You should have each of the following steps performed by a professional at the end of your warm season and before you begin using your chimney in earnest:
- Check the exterior – look for spalling, crumbling or chipped masonry. Make sure that it isn’t leaning. Don’t forget to look in the attic if your chimney is exposed there.
- Check the chimney cap and replace it if it is showing wear.
- Check the roof – look for signs of leaks or staining around the chimney. If your flashing is failing it must be repaired right away. If you have access, check the roof from underneath as well.
- Check the flue – Look for soot and creosote buildup and make sure there are no cracks in the liner.
- Check your fireplace – Clean it down to the fire bricks and look for cracks, wear or signs of water infiltration.
- Check your damper – make sure that your damper is opening when you release it and sealing properly when you pull it closed.
Periodic
If your brickwork requires a sealant you should reapply the sealant every five years. If you have painted brick keep an eye on the state of the paint on your bricks and repaint as needed.
Common Repairs
Your average chimney won’t need repairs very often. In fact, you could see a decade pass by before you have to perform your second repair. However, there are a number of repairs that are considered common.
Brick Repair
The brick forming the outer layer of your chimney goes through a ton of stress. Heat from the flue and the constant assault of weather conditions can take a huge toll on your brickwork. Here are a few of the problems you may encounter.
Spalling
Spalling is just another way of saying crumbling. The face of your brick will crack and fall away. This is usually the result of water damage which is most often caused by our next issue. Your mortar could also wear away or crumble.
Damaged Crown
The crown of your chimney should be a single, smooth slab of poured concrete that is slightly raised in the center and has a slight overhang on all sides.
It’s sole job in life is to shed water while keeping it from infiltrating your brickwork. A cracked, worn or poorly designed crown will cause your brickwork to spall over time.
Broken Damper
When your damper gets worn or fails to open you will either get airflow when you don’t want it or smoke that fills your home instead of flowing up the chimney.
There are two types of dampers: throat dampers and top dampers. Older homes will have throat dampers built into the masonry at the throat of your chimney.
Most manufacturers and almost all service companies do not offer parts or service for masonry based throat dampers. The reason is the simplicity of the top damper. It is far easier to remove the damaged damper plate at the throat and install a top damper than it is to try to revive the old damper.
Top dampers sit on top of your chimney with a cable running down your flue which is then held in place by a bracket. It allows you to adjust your airflow but only before you light your fire, as the bracket sits inside the firebox.
The seal quality of a top damper is superior to that of a throat damper and is as certain a seal of your chimney as a cork is to a bottle of wine.
While well designed, top dampers are exposed to the weather and may need replacement at some point in time. Be sure to check for wear and tear during your annual inspections.
Liner Issues
Consider your liner as your safety system for your chimney. Any problems with your liner can have devastating effects on your home.
If your liner is cracked, or just worn down to nothing, it can’t protect your flue from the extreme heat running through your chimney.
This can cause your flue to break down which will allow that heat to reach the combustible structures in your home and cause a fire.
Your liner can also collect creosote, a byproduct of burning wood, which can cause a chimney fire if allowed to build up over time. Liner maintenance is your best way to keep your chimney safe to use.
Damaged Flashing
Chimney flashing is essential for keeping the water that runs off your chimney from getting under the shingles on your roof. You should take care of any problems with your flashing immediately after they are discovered.
When installing or repairing flashing, be certain to groove your brick or mortar and shape the flashing to fit into that groove. Then seal it to prevent any water from getting behind the flashing, as you see in the image to the right.
Your flashing should also sit beneath your roof shingles with appropriate sealant applied.
Specialty Tools
We wouldn’t recommend purchasing many of the tools of the chimney trade for your personal use. The cost is too high to justify for such occasional use.
However, there are items you may want to rent when you have a repair to perform, such as:
- Mechanical creosote removal tools
- Lifts (preferable over ladders)
- Scaffolding
- Rooftop safety harnesses
- High power vacuum systems (250cf per minute minimum)
- Chimney brushes
- Rotary cleaning tools
There are some tools that aren’t too costly and will have uses outside of chimney repair. The following tools are necessary for such repairs[3]:
- Masonry bits, chisels, hammers, and trowels
- Hand brushes (steel bristle)
- Pointing tools (for shaping mortar)
- A good selection of wrenches, pliers, and drivers
- Heavy duty drill (not hammer drills)
- Wrecking, pinch and pry bars
- Variety of sledge hammers
- Large tarps
- Drop Lights
Certain chemicals and sealants will also be required but should only be purchased when needed.
Safety
Chimney repair will often involve dangerous heights whether you are working on the side of your house or up on your roof. Be sure to take proper safety precautions at all times. DO NOT BE THE GUY IN THE IMAGE ABOVE! He’s an idiot, and we’re sure his family misses him.
If you can set up a rig similar to the one seen in this video (but add safety harnesses) it would be ideal. At a minimum you should be using:
- Safety harnesses
- Lifts instead of ladders
- Scaffolding
- Hard hats
- Safety glasses
- Respirators
- Gloves with hand protection
Now it’s time to get out there and take a good hard look at your chimney. If you see anything wrong, you know where to find the answers. Good luck!
