CRACKED CHIMNEYS, MASONRY BLOCK - CONTENTS: Detailed Inspection & Photo Guide to diagnosing and acting on cracks in a concrete block chimney. Cracked concrete block chimneys risk unsafe chimney flues, presenting fire and flue gas hazards in buildings. Common Causes of Concrete Block ("cinder block")
Chimney Cracking. Evidence of Prior Repairs May Indicate a History of Chimney Cracking & Movement in a Concrete Block Chimney
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Concrete block or cinder block chimney cracks & damage: this article describes cracks in masonry block or concrete block chimneys and suggests possible causes and crack severity.
These articles on chimneys and chimney safety provide 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.
We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
Cracked concrete block chimneys risk unsafe chimney flues, presenting fire and flue gas hazards in buildings
Both outdoors and indoors we may also see chimney cracks which could be due to chimney movement (introduced above) or due to compression loads or other chimney construction problems (photograph below).
Our photo (left) illustrates serious frost cracking damage in a concrete block (or masonry block or "cinder block") chimney serving a home in upstate New York. Notice that there is no rain cap and no chimney cap protecting this chimney against water intrusion - defects likely to lead to frost damage and an unsafe flue, especially in freezing climates.
Cracks in a masonry block chimney always deserve further investigation to identify the probable cause, to decide on the remedy and to evaluate the safety and function of the chimney.
We recommend that you have any cracked or damaged chimney thoroughly inspected by a professional, including an inspection of the integrity of the chimney flue and of any fireplaces or other attached heating systems.
Common Causes of Concrete Block ("cinder block") Chimney Cracking
Our photo (left) illustrates a concrete block chimney suffering from both extensive cracking as well as spalling surfaces (CHIMNEY SPALLING). We think there are leaks into the internal structure of this chimney, probably originating at the chimney cap.
It looks as if someone thought they might repair the chimney by coating its exterior with a masonry sealer paint or a thin stucco covering. But as leaks are originating from the chimney top and passing within the chimney structure, that repair did little good.
Cracks in a masonry chimney, particularly concrete block chimneys (this article) and perhaps brick may be caused by
Watch out: a chimney fire, even if it does not set the building ablaze, is likely to have caused serious damage to the chimney itself, leaving it unsafe, as may other chimney cracks or movements for any reason. The risks include building fires, potentially fatal flue gas leaks, improper draft, and unsafe heating equipment operation.
Our photo at left shows dangerous cracking indoors in a concrete block chimney used to vent a heating appliance.
You might also notice that the barometric damper is not level - a much simpler problem to correct.
As a chimney leans away from the house we might find several serious problems caused by that movement:
Damaged, unsafe chimney liner (flue gas leaks or sparks into the building interior, a fire or potentially fatal carbon monoxide hazard)
Damaged, unsafe fireplaces where the chimney has pulled the firebox
away from the building or created dangerous openings around the fireplace into the
building structure, risking both sparks (and fire) or air leaks (and inability
to control the draft).
Leaks into the building walls (flue gas leaks or sparks into the building interior, a fire or potentially fatal carbon monoxide hazard)
Unsafe fireplaces in the building: hearth cracks, fireplace side cracks, chimney damage all present risks of sparks or smoke entering the building cavities, a fire and flue gas risk. Check for evidence of movement at the fireplace. (Flue gas leaks or sparks into the building interior, a fire or potentially fatal carbon monoxide hazard)
Evidence of Prior Repairs May Indicate a History of Chimney Cracking & Movement in a Concrete Block Chimney
If you see repairs such as shown in the our photo (left) the chimney should be professionally inspected, especially to establish the condition of the flue liner as it may be unsafe.
Our pen points to a gap between masonry block chimney and a building wall, indicating chimney movement and raising question about other less obvious crack and damage to this structure.
It may be possible to repair minor chimney racks with masonry products provided that the underlying cause is also identified and corrected.
Also, some concrete blocks may be cracked during their individual drying/curing process, a condition not to be confused with chimney cracking.
The usual repair when a significant chimney crack has occurred, damaging the chimney and the flue is to remove and replace the chimney, though in some cases it may be possible
to re-line the chimney and to jack an intact masonry chimney back to level and repair its connections into the building.
Repairs to Cracked Concete Block Chimneys
Extensive concrete block cracks, badly damaged masonry chimney flues, curved, leaning, broken masonry chimneys may need to be re-built to be safe and functional. But minor chimney damage, and chimney damage that is confined to just above the roof line can usually be repaired or re-built.
Watch out: be sure that the roof surface is protected from damage during rooftop chimney repairs, otherwise your chimney may be fixed but you could end up needing a new roof. Also see CHIMNEY REPAIR METHODS.
Question: I was told that the building code in Massachusetts only allows block chimneys to be reparied with bricks
2017/04/26 Eddie Arroco said:
I need my fireplace chimney concrete blocks repaired or replaced above the roofline which are cracked and breaking up. I called in a contractor but I was told that the building code in Massachusetts only allow him to replace the blocks with bricks.
I'm afraid the bricks wihich is of different color will not look good at all. Is there any truth to this code since it is only a repair of existing structure? What do you suggest I should do? I would really appreciate your advise. Thank you very much.
Reply: Really? Ask again. Here are the Massachusetts Chimney Codes based on model building codes
I am really surprised at the claim that concrete block chimneys are not permitted in Massachusetts.
And I'm doubtful. It might be that the mason wants to work with and use the materials with which she is most-comfortable.
But on occasion a builder speaks as if God told him the Truth when in fact he has never read even the instructions on the box of the device he's installing.
Take a look at these two Massachusetts chimney code documents and you will see that the words "brick" or "concrete block" do not appear anywhere in the code.
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(Dec 18, 2012) chimney man said:
I just finished a blcok chimney with clay liner. 28 ft tall. i did it in cold weather but used a space heater.. days later to keep it warm i started a small kindling fire in the cleanout door.. half hour and let it go out. the next day i realized the block right above the cleanout door the mortar joint was cracked all the way around. the tile was not. and the thimbal is 4.5 feet about the cleanout. so heat wont touch that part from this point on once i get my stove in there. i dont know why this happened. is it bad and what shuld i do?
(July 31, 2014) alan said:
I've got a question about a home that i saw on your web page, the picture shows the chimney in the back yard next to the deck and the house is tan with a brown roof. what kind of material is the outside of that chimney. It looks like some sort of vinyl paneling. The reason i ask is because we have a brick fireplace that has been worked on 3 times over the last 15 years, we even had it torn down to the rooftop 8 years ago. Anyway, the inside of the chimney is solid per inspectiors, but the outside, even the newest part continues to pop and break. I am looking for something new and cheaper to repair my chimney, would be nice to shore up the current chimney, and then put paneling around it. is this possible, and if so can you recommend a contractor in dayton ohio area that you work with? thanks for your help.
Alan, I don't see the photo you describe in the article above. But indeed some chimneys are constructed as an insulated metal flue run inside of a vertical wooden chase whose exterior is covered with a choice of siding materials.
Details are at
Note that this is NOT a way to repair a damaged masonry chimney if the flue is unsafe. But it MIGHT be possible to surround and cap a safe masonry flue with a new external chimney chase.
I'd be more tempted to simply stucco the chimney exterior of a spalling masonry instead.
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Questions & answers or comments about diagnosing & repairing cracked concrete block or masonry block chimneys.
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Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: firstname.lastname@example.org
Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at email@example.com
Roger Hankeyis principal of Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
NFPA #211-3.1 1988 -
Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
NFPA # 54-7.1 1992 -
Specific to venting of equipment with fan-assisted combustion systems.
Gas Appliance Manufacturers' Association has prepared venting tables for
Category I draft hood equipped central furnaces as well as fan-assisted
combustion system central furnaces.
National Fuel Gas Code, an American National Standard, 4th ed. 1988 (newer edition is available) Secretariats, American Gas Association (AGA), 1515 Wilson Blvd., Arlington VA22209, and National Fire Protection Association (NFPA), Batterymarch Park, Quincy MA 02269. ANSI Z223.1-1988 - NFPA 54-1988. WARNING: be sure to check clearances and other safety guidelines in the latest edition of these standards.
Fire Inspector Guidebook, A Correlation of Fire Safety Requirements Contained in the 1987 BOCA National Codes, (newer edition available), Building Officials and Code Administrators International, Inc. (BOCA), Country Club HIlls, IL 60478 312-799-2300 4th ed. Note: this document is reissued every four years. Be sure to obtain the latest edition.
Uniform Mechanical Code - UMC 1991, Sec 913 (a.) Masonry Chimneys,
refers to Chapters 23, 29, and 37 of the Building Code.
New York 1984 Uniform Fire
Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements
New York 1979 Uniform Fire Prevention & Building Code, The "requirement" for 8" of solid masonry OR for use of a
flue liner was listed in the One and Two Family Dwelling Code for New
York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979
Building and Fire Prevention Code:
"Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
"Rooftop View Turns to Darkness," Martine Costello, Josh Kovner, New Haven Register, 12 May 1992 p. 11: Catherine Murphy was sunning on a building roof when a chimney collapsed; she fell into and was trapped inside the chimney until rescued by emergency workers.
"Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
"Chimney Inspection Procedures & Codes," Donald V. Cohen was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman, then editor/publisher of that publication. The production of the ASHI Technical Journal and future editions was cancelled by ASHI President Patrick Porzio. Some of the content of Mr. Cohen's original submission has been included in this more complete chimney inspection article: InspectAPedia.com/chimneys/Chimney_Inspection_Repair.php. Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
US Energy Administration: Electrical Energy Costs http://www.eia.doe.gov/fuelelectric.html
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Ceramic Roofware, Hans Van Lemmen, Shire Library, 2008, ISBN-13: 978-0747805694 - Brick chimneys, chimney-pots and roof and ridge tiles have been a feature of the roofs of a wide range of buildings since the late Middle Ages. In the first instance this ceramic roofware was functional - to make the roof weatherproof and to provide an outlet for smoke - but it could also be very decorative.
The practical and ornamental aspects of ceramic roofware can still be seen throughout Britain, particularly on buildings of the Victorian and Edwardian periods. Not only do these often have ornate chimneys and roof tiles but they may also feature ornamental sculptures or highly decorative gable ends. This book charts the history of ceramic roofware from the Middle Ages to the present day, highlighting both practical and decorative applications, and giving information about manufacturers and on the styles and techniques of production and decoration.
Hans van Lemmen is an established author on the history of tiles and has lectured on the subject in Britain and elsewhere. He is founder member and presently publications editor of the British Tiles and Architectural Ceramics Society. Available at the InspectAPedia Bookstore.
Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003 - These guidelines address the inspection of chimneys and stacks. Each guideline assists owners in determining what level of inspection is appropriate to a particular chimney and provides common criteria so that all parties involved have a clear understanding of the scope of the inspection and the end product required. Each chimney or stack is a unique structure, subject to both aggressive operating and natural environments, and degradation over time. Such degradation may be managed via a prudent inspection program followed by maintenance work on any equipment or structure determined to be in need of attention. Sample inspection report specifications, sample field inspection data forms, and an example of a developed plan of a concrete chimney are included in the guidelines. This book provides a valuable guidance tool for chimney and stack inspections and also offers a set of references for these particular inspections.
NFPA 211 - 3-4 - Clearance from Combustible Material
NFPA 54 - 7-1 - Venting of Equipment into chimneys
Brick Institute of America - Flashing Chimneys
Brick Institute of America - Proper Chimney Crowns
Brick Institute of America - Moisture Resistance of Brick
American Gas Association - New Vent Sizing Tables
Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
National Chimney Sweep Guild - Yellow Pages of Suppliers
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones