Repairs for cracked chimney top crown or damaged top clay flue tiles:

This article describes chimney top repairs for masonry chimneys and clay flue tiles, work performed at or from the rooftop. This website provides detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed.

Repair of Damaged Clay Chimney Flue Liners at the Rooftop

Determine the Extent of Chimney Damage and the Safety of the Entire Chimney Flue

Our photo above shows an unsafe chimney that was still in active use. Notice those missing bricks and lost mortar? Damaged chimney top masonry such as missing bricks and a missing chimney cap were easily spotted from ground level, raising a critical concern for the fire and gas-leak safety of the clay flue tiles lining this chimney.

[Click to enlarge any image]

At the front left corner of the clay chimney flue tile you can see our pen inserted into an opening between the chimney flue tile and the (damaged) surrounding brick and concrete chimney structure - water entering the chimney structure at this location risks freeze damage to the chimney flue itself, resulting in potentially very dangerous conditions.

First, you will want to be absolutely sure that the chimney damage, whether to the ceramic clay flue liner or to the surrounding masonry or both, is limited to the upper, visible, accessible part of the chimney. Our chimney clay flue tile liner damage photos above show enough wear and cracking (above left) and opening between clay flue tile liner sections (above right) that further inspection and repair by a chimney professional is warranted.

Other chimney damage lower in the chimney itself as it passes through or alongside the building could be very dangerous, even fatal if carbon monoxide or other flue gases leak into the building or if sparks cause a fire.

Our photos above show damage to the chimney clay flue tiles near the chimney top, with multiple cracks in the clay flue liner (above left), and severe spalling in the clay flue tile liner (above right) -these are two different chimneys.

Both need repair. The right hand chimney (above right) may need a complete re-lining while the chimney at above left might be damaged only above the roof line, making roof top repair a reasonable approach.

We suggest that you hire a professional chimney sweep who can examine the entire chimney flue. Most chimney sweeps also offer repair services, and can suggest what repairs are needed and give alternatives for the particular chimney and flue on your building.

Reline the Chimney versus Repairs Just at the Chimney Top

Our photo of spalling brick near the top of this masonry chimney (left) shows damage almost certainly caused by frost. Without a view of the chimney top, however, we don't know exactly where water was leaking into the structure, nor the condition of the flue liner itself. It is the condition of the fire clay (or as some call it "ceramic") flue liner that is of course critical to safe venting of flue gases outside.

Some chimney repair contractors will want to reline the whole chimney flue - an approach that is often safe, quick, easy, and profitable. But this approach may be inappropriate if the damage is just due to weather at the chimney top and the rest of the flue is intact and safe.

Water leaking between the flue liner and the masonry surround is also a very common cause of water and frost damage at the chimney top.

Most often we see spalling flue liners and loose or damaged bricks or concrete block around a chimney top caused in large part by failure to protect the chimney to from the weather; lack of an allowance for thermal movement among chimney parts, especially the liner and the surrounding masonry,can also crack and break the flue liner, especially on the above-roof portion where the chimney is in northern climates exposed to coldest temperatures.

Potentially, damage to the masonry chimney structure as well as to its clay flue tile liner can occur also inside a freezing attic space.

If the damage is just at the top of the chimney and its masonry flue liner, repairs can usually be completed entirely from outside, working from the rooftop. (Be sure the mason performing the repairs protects the surrounding roof surface from damage lest your chimney repair be followed by roof leaks.)

Other Chimney Top Repairs for Damaged Flue Liners or Surrounding Masonry

Some people try patching the damaged areas of the chimney top or chimney flue with refractory cement but we don't recommend applying "patches" to the interior of a chimney flue: there is a risk that the "patch" might later fall into and block the flue - a very dangerous condition.

A better approach and the one used by most chimney repair masons who are not going to simply reline the flue, is to remove all of the damaged materials down to sound chimney flue liner and brick or block, then rebuild with new clay flue liner and brick (or block), adding an appropriate chimney cap and top seal.

Using solid masonry between the clay liner and the surrounding masonry at the chimney top is a common practice (photo at left), and having inspected quite a few chimney tops, we can't say that every chimney built this way fails, but it is not the best practice and is not recommended by experts.

Our chimney top photo (at above left) shows that this roof top chimney seal is already cracking, threatening future damage to the chimney flue liner as well as the chimney structure at roof top.

Other problems at this chimney top include the termination of both flues at the same height, and the absence of any rain cap.

Using a fire-safe flexible caulk at that joint will reduce the chances of cracking due to temperature differences.

Carson Dunlop Associates [at REVIEWERS] sketch ( above-left) show some details of good chimney cap construction. The object of these details is to avoid water and frost damage to the flue or to the chimney itself.

See CHIMNEY INSPECTION ROOFTOP for these chimney top inspection and final repair and sealing details.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-12-13 by Inspectapedia Com Moderator

@Anonymous,

Thanks for the helpful photo of a bad chimney design: putting a chimney smack in a roof valley blocks valley drainage and invites leaks.

I can't see enough to be sure but this looks like someone added a stone veneer (with no bottom flashing) onto some other type of chimney.

See solutions to this bad chimney location found at

CHIMNEY SADDLE / CRICKET FLASHING

that is found in our article

FLASHING, CHIMNEY MISTAKES & LEAKS

On 2021-12-11 by Anonymous

On 2021-12-11 by Inspectapedia Com Moderator

@Paul,

Darn. I'm over-challenged by your perfectly-fair question: is it safe to continue using our fireplace?

Your description of the apparent risk: a crack in a (solid masonry with clay flue tile liners, right?) chimney that is found 10 feet above the roof line and nowhere near any combustible material as being low-risk, sounds reasonable on the face of it.

Picture me, an experienced and really old building and environmental guy, sitting at my nice wood desk in Poughkeepsie, trying to be useful to a reader whose expertise and experience I don't know, at a building I've never seen, located I don't know where, in an unknown condition, of an unknown age, construction, climate, and a host of other risk-relevant factors.

Isn't it all clay, brick and mortar above the roof?

Yes, that's what we'd expect, but a long experience says to expect the unexpected.

So before we bet your life and that of your family or other home occupants on a remote consult, with apology, I have to say that before using the fireplace (wood-burning we are guessing) it would make everybody safer if you could have (or have already had) a complete chimney flue inspection by a qualified expert (such as an inspector certified by the Chimney Sweeps Guild if you're in the U.S.).

• Is that the only chimney damage?
• Is there already a creosote problem and risk of a chimney fire?
• Is the crack a fine and low-worry one in an intact solid masonry (with normal air gaps) chimney, or is the crack we've seen the tip of an iceberg of trouble - that is, what's the risk that the chimney masonry is damaged enough that you build a fire and pieces of the liner fall out and the chimney becomes immediately dangerous both above the roof and lower in its run up through the building.
  

If your flue has already been inspected and found absolutely wonderful: clean, safe, un-damaged, properly constructed, sized, etc. except for what the inspector considers a minor damage near the chimney top, then that onsite expert might feel it safe to say sure go ahead and enjoy some holiday fires.

The photo I show below is discussed above on this page and is, of course not YOUR chimney. Have you got a photo of your chimney crack and a copy of a chimney inspection report?

On 2021-12-11 by Paul

Our chimney extends about 12 feet above the roof line. We just discovered a crack in the interior clay flue near the top. It extends about 2-3 feet down from the top. Where the crack ends is still 8-10 feet above the roofline.

Are we at risk using the fireplace for the few weeks left before we can get the chimney flue relined?

Does it even need relined if the crack is that far above the roof line? If the crack is that far above the roof line, if an ember did get lodged in the crack, what is there to catch fire? Isn't it all clay, brick and mortar above the roof?

On 2020-09-17 by danjoefriedman (mod)

Remove the loose concrete and seal anew; Use flexible sealant at the intersection of the top seal or crown and the clay flue tile liner (where you see a gap in your photo) for a more-durable seal.

Usually the smaller flue is for a heating appliance and the larger flue is for a fireplace.

More about chimney flues, flue sharing, inspection, safety, etc. are in the ARTICLE INDEX to CHIMNEYS & FLUES
given above

On 2020-09-17 by Dave

@danjoefriedman,

Thank you for the response. I know nothing about this stuff or what the difference is between the flues but only cap the large one? Think I can get away with resealing around the edges or just chop away all the old mortar and start fresh?

On 2020-09-15 by danjoefriedman (mod)

Dave:

That chimney could be or become unsafe from water damage; the top seal or crown around the flues is cracked and leaking; there are no chimney caps.

At the very least I'd make those repairs.

If the larger flue - presumably an unused fireplace - is not in use and is not connected to any fireplace nor other heating equipment at all, then you could cover it with slate or stone;

On 2020-09-15 by Dave

Hi - my house was built in 1952, so I’m sure this hasn’t been touched since. I know I have to do some flashing repair but this is not working chimney like we have a fireplace or anything.

Forgive my ignorance, but should I be concerned that water is doing damage in between the clay pipe and broken mortar?

On 2020-05-18 by danjoefriedman (mod)

Certainly, Brenda, it's possible to repair or replace the topmost chimney tile(s) as long as there's access.

Broken tiles further down in the flue can sometimes be repaired too

On 2020-05-18 by Brenda

Hi: The terracotta that extends outside of the chimney has some minor damage. Is it possible to repair that part of the terracotta/clay flue without having to put in a stainless steel flue?

On 2017-09-30 by Steve

You will cap the entire top of the chimney. Attaching to the side of the chimney.

On 2017-02-03 by Valerie

How do you cap the flues that are level with the cement? In the following example: "...the termination of both flues at the same height, and the absence of any rain cap."

Since the cap goes on the outside of the flue and is not inserted inside -- unless there's a cap that's inserted inside?

My flue is even with the concrete with nothing to grab onto, like the example above. I don't use the fireplace and just want to cap it to keep nesting birds out. Thanks

Question: chimney sweep opinion on chimney safety

(Sept 24, 2011) Sarah L said:
Hi,
I have been told by a chimney sweep that i have a liner that is suitable for an open fire. Would this be adequate for multi fuel stove (wood and coal) and if so would i need any lining further down the chimney to connect a stove to the chimney. When talking to or reading up on manufacturer websites it seems that they advise a lining which can cost almost as much as the stove.

Is this necessary? When I have peered into the chimney myself I cannot see any liner only bricks but there is a bend in the chimney and i cant see all the way up to the top; do you think there still is one there or should i get a second opinion? If so how can I get an independent one from someone who is not trying to sell me something? Thanks.

Reply:

Sarah if you see only bricks, at least part of the chimney is unlined. Still we don't know it's safety - for example we don't know if the chimney is built with a single brick (wythe) thickness or more bricks were used. A single-brick wythe chimney would be unsafe for most applications.

I'd call a different chimney sweep and get more explicit details on the chimney construction, materials, condition, and safety before I'd consider using it. Chimney fires are really dangerous and not something on which to risk a short cut. Perhaps a sweep certified by one of the certifying agencies would be more reliable.

see

Chimneys Cleaning Advice, Procedures

Question: Blocked flue at Parkray Fire with Back Boiler

(Apr 17, 2012) russell s said:
hi we had a parkray fire with back boiler in our current propperty when we moved in 5 years ago and 2 years ago this was removed by housing association and exchanged with oil central heating,

however last year we decided to fit a woodburning stove with no back boiler and have this as a cheaper alternative to using the oil for the heating, however we had it swept in july last year and used it regularly until

about 2 weeks ago when we noticed it wasnt drawing properly and assumed it just needed sweeping however when we were letting it go out by itself

we noticed smoke coming from a crack in the plaster above our brick fireplace from the wall does this mean the clay liner originally fitted must be damaged or could just be blocked as i noticed last week sea gulls are dropping twigs and building a nest on top of it, please help thanks

Reply: we noticed smoke coming from a crack in the plaster above our brick fireplace

Russell

I do not understand all of our question, not knowing what a "back boiler" is - perhaps you mean a backup heating system ? In any case,

Watch out: I would IMMEDIATELY STOP USING THAT SYSTEM AND CHIMNEY - you are describing what sounds to me to be a very serious building fire and flue gas leakage hazard. Indeed, on 12/31/1969 I was in a house that caught fire afber being preceded by just about the same symptom.

You need the chimney inspected by a professional chimney sweep who can examine the entire flue interior and tell you what work is needed. Probably reconstruction or relining.

Birds might block the top of the chimney - that's bad enough, but smoke coming out of the wall above the fireplace means you are about to burn your house down.

...

Continue reading at CHIMNEY REPAIR METHODS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CHIMNEY DEFINITIONS
• CHIMNEY CAP & CROWN DEFINITIONS
• CHIMNEY COMPONENT DEFINITIONS
• CHIMNEY DRAFT & PERFORMANCE
• CHIMNEY INSPECTION DIAGNOSIS REPAIR - home
  • ATTIC CHIMNEY INSPECTION
  • CHIMNEY CLEANOUT DOOR INSPECTION
  • CHIMNEY FLASHING MISTAKES & LEAKS
  • CHIMNEY FLUE INSPECTION CAMERA
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  • CHIMNEY INSPECTION INDOORS
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  • CHIMNEY INSPECTION PROCEDURE SUMMARY
  • CHIMNEY INSPECTION at ROOFTOP
  • CHIMNEY TOP MASONRY DAMAGE
  • FLUE TILE DAMAGE in CHIMNEY
• CHIMNEY RE-LINING CHOICES
• CHIMNEY REPAIR METHODS

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CHIMNEY REPAIRS, TOP & CLAY FLUE TILE at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES

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