Masonry Chimney Crack Diagnostic FAQs

Q&A on how to diagnose cracks in chimneys.

This article series describes the types of chimney cracks and movement that may be found in brick, stone, or concrete block chimneys.

Cracked Masonry Chimney FAQs

On 2019-02-08 by torres.mayra.g

I am interested in buying a house. However, I am concern because the chimney has many cracks. What could the cause of such cracks be? [See photo above]

These questions & answers about interpreting cracks or signs of movement in masonry chimneys were postd originally at CHIMNEY CRACK DETECTION & DIAGNOSIS - be sure to review that article as a good starting place for understanding the impact of and meaning of signs of damage to brick, concrete block, stone masonry chimneys.

by (mod) - hairline cracks through the middle of bricks

Mayra

In your photo I see fine hairline cracks right through the middle of what looks like bricks - in a brick and mortar masonry chimney.

I have so little information that I can only guess that the bricks may have cracked from thermal changes in the chimney or maybe even overheating.

You would be wise and safer to have the chimney inspected by a certified chimney sweep (National Chimney Sweeps Guild if you are in the U.S.)
not just for the crack we see, but to assure that the interior flue is intact and safe.

IF the chimney is indeed significantly damaged it may be repairable by re-lining, but gee that's just speculation from a very limited image.

On 2019-01-14 by Terry

Something is leaking through the drywall and paint upstairs on the chimney stack that runs from the attic down to the basement. It resembles beeswax??

by (mod) - chimney wax - may be honeybees

That's possible, if it's actually waxy - honeybees sometimes make wax honeycomb in building cavities

Attach a sharp photo to a comment or two

On 2018-10-17 by Janet Concern about crack in a shared chimney

There is a crack running up one side of my chimney and down about a 1/3 my neighbours side.

I wanted to get this repaired urgently but the neighbour has said their builder told them that my loft conversion (completed before I moved in and about 20 years ago) 'broke' the chimney.

He said there is nothing wrong with his chimney (not separate) and that its all on my side. He has since refused to talk about but I am concerned the chimney may fall off the roof. I am about to get a survey, possibly pay for the work myself (about £4-5K) and take them to court if I can prove joint responsibility.

Also, when it rains, I get water dripping in through my front bay window. Any suggestions very gratefully received.

by (mod) - first concern is chimney venting safety and avoiding a building fire

Janet

The very first concern is chimney venting safety: if there are cracks in a chimney there is risk that the interior flue could be damaged as well; if the flue is damaged flue gases, including sparks (risk a building fire) and combustion gases (fatal carbon monoxide poisoning could kill building occupants) might enter the building with dire consequences.

So your chimney inspection should include a complete inspection of the flue interior.

Water leaks around a chimney can lead to frost damage - freezing - that can cause or contribute to cracking damage.

Without a detailed inspection of your building and its chimney one can't diagnose the cause nor the role played in damage by prior construction.

An expert chimney weep or inspector ought to be able to comment as well on the cause of damage.

You can also attach photos using the Add Image button and we may be able to comment further.

On 2016-10-23 by Anthony

I have a odor that has caused us to move out of our home. I believe it is coming from my fireplace.

A few years ago we had new liners put in both chimney stacks (fire place and hot water heater side) and had the fire box rebuild. It seems fine for the first 3/4 years but now the odor of old dirty cinders and creosote is overwhelming.

The fire box was rebuild due to damage from a tree falling onto the house. Is it possible for the front veneer stone to have been cracked internally and the odor is coming through the interior stone veneer into the living area. If so is there a way to check this with out ripping out the entire veneer front?

The house is a well maintained rancher with full basement and attic build in the 40's. Any thoughts would be appreciated, Thank you.

by (mod) - cracked chimney, firebox, hearth or other components would be unsafe,

A cracked chimney, firebox, hearth or other components would be unsafe, risking a building fire, flue gas leaks into the home, and if leaks pass from a heating flue to the fireplace flue and down into the occupied space, there is risk of both heating system improper operation and fatal carbon monoxide poisoning.

A careful inspection by a certified chimney sweep, perhaps with some smoke testing, should sort out the trouble.

On 2016-02-19 by Anonymous

About a week ago, my furnace stopped running efficiently. My furnace repair guy said the furnace has no obvious issues but it went off when reinstalling the cover, indicating it was not properly venting.

Upon inspection, the tube sounds dense when knocking on it, as if it is now blocked by debris.

In addition, there is only a small amount of smoke visible exiting the top cap compared to other chimneys. I believe the debris resulted from the neighbors chimney liner being replaced 1.5 years ago.

We share a chimney and half way through the job, I heard what sounded like gravel falling into my side of the chimney and into the basement area where the vent tubes run.

The company had also already removed my top cap without consent and claimed they were unaware that the unit was two separate homes. my concern is that the company removed some of my liner thinking it was the homeowner who contracted with them in in so doing, f

ailed to replace or repair their error causing my chimney to deteriorate in this time to where it is almost fully blocked. I called that company to ask them to be accountable for the mistake and they began to explain that a home from 1954 has debris fall over time and that it's perfectly normal for debris to be blocking the furnace exhaust.

Care to weigh in? I would love not to have to fork over $2k for a new chimney liner unless it has died of natural causes vs. Chimney company mistake.

This house was bult in 1950 nothing has been dome with the brick jhas crack and needs mortor.

by (mod) - Safety warning about dense soot in chimney

Weighing in with the reclama that I'm offsite and that onsite there will ALWAYS be additional, important findings:

1. It is common but not "normal" in the sense that it's not "acceptable" for a chimney to be blocked.

It's an unsafe condition. A chimney can be blocked by animals nesting (if a cap has been removed), or by soot, creosote, or by falling debris if the flue is not in good condition.

2. It sounds odd for two homes to be sharing a chimney, you will want to search InspectApedia for SHARED CHIMNEY & FLUE HAZARDS to read about the hazards.

Basically both homes, assuming each is venting an oil fired heater, require individual flues and those flues must be separated by at least a wythe of brick or other masonry inside the chimney. Any damage that makes an opening between flues is unsafe.

3. Before pointing fingers and getting into an unpleasant fight, start by hiring a professional chimney sweep. Ask for a complete inspection of the entire flue for safety. If the flue is safe and intact, have it cleaned.

4. Check the oil burner performance, measurements, settings, to be sure it's not making excessive soot.

Watch out: If your system is GAS fired heat turn it off IMMEDIATELY as soot and blocked flues risk fatal carbon monoxide poisoning.

So how do you fix a chimney crack?

How do you repair this? Mine is just like the picture as it goes through the mortar and the brick. It originated from the air vent, I assume because the metal air vent got hot. Thanks.(Sept 22, 2011) Fishin

Reply:

If a chimney has minor cracks but is structurally sound it may be repaired by re-lining. If the chimney is in danger of collapse it should be removed and replaced. You need an on-site expert to make such a determination. Don't forget to have the flue interior inspected for safety before using such a chimney at all.

 

Smoke is coming out of cracks in our chimney

I have installed about 20 woodburners, and always have them signed off by hetas engineer.... At my own house i have recently fitted wood burner about 5kw, stainless 316/316 flue, pot, ufo cowel. next door is getting smoke done her living room chinmey which has all pot capped on room with pepper posts.

I taped the pepper pots up with gaffa and smoke bombed the fire next door up the flue - it came out of cracks in mortor and around pepper pots still. could it pull down through these cracks and fill the living room next door??? (raised pot from standard to 600mm high laready to try aid the problem. (Sept 26, 2012) david

Reply: immediate fire and CO hazard - unsafe house

Watch out: you are describing both a house fire hazard and a chimney operation and draft problem. It's time for a professional chimney sweep's inspection.

 

Do we need to fix gaps at the fireplace sides?

Last night as my husband built the first wood fire of the season in our fireplace, I noticed a gap between the fire bricks lining the inside of the fire box. The opening was between the bricks on the right side of the fire box and the back of the fire box.

When the fire died down, I used the metal fire poker and found I could insert the poker through the gap in the bricks to the metal fire box liner. Is this dangerous? Should I arrange for a fireplace and chimney inspection? My husband doesn't think it's a problem. Thank you. (Nov 16, 2014) Jeannie D

Reply:

Absolutely, Jeannie,

Watch out: the opening you describe could be a serious fire hazard. It may also introduce draft problems that interfere with chimney operation.

 

OK to use a cracked chimney pot?

I have just re-opened my fireplace to make an open fire. I have a chimney pot to put on but it has a vertical crack in the side ... can this still be used in its current state? if not can it be repaired?(Nov 30, 2014) Clair

Reply:

Clair I'd replace the cracked chimney pot rather than trying a repair. You might be able to fill the crack with cement or even an epoxy, but exposed to the weather I'd not expect it to last.

...

Continue reading at CHIMNEY CRACK DETECTION & DIAGNOSIS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Chimney Collapse / Crack Articles

• CHIMNEY COLLAPSE RISKS, REPAIRS
• CHIMNEY CRACK DETECTION & DIAGNOSIS - topic home
• CHIMNEY DAMAGE by LEAKS & FROST

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