Chimney leaks frequently come from three common areas on fireplace chimneys. Chimney crown leaks, chimney flashing leaks, and brick chimney leaks. Different factors affect a chimney’s ability to resist water penetration such as the age of the chimney, the type of construction materials and its construction. In this article I’m going to reveal some specific problem areas and how you can solve your own chimney leaks.

Chimney Crown Leaks

 

chimney crown repair
Using Brushable CrownCoat for chimney crown repair

 

First off, the chimney cap or masonry chimney crown. Over time, chimney crowns can crack or break off, allowing water to soak in and come inside the chase. This water can run down the chimney and absorb into the inside of your house. Additionally, crowns need to be made of concrete. However they are frequently made from mortar instead to save time and money.

The problem is that mortar is not as dense or as strong as concrete and is more likely to absorb water. If the crown is in too bad of shape, you may need to replace the crown. That can usually run anywhere between  $500-$2,000.

If there are some severe cracks, but no missing pieces off the crown, my chimney sweep crews usually use a product called CrownSeal. It’s a flexible elastomeric product that you can trowel on over the surface of the crown. It fills in the gaps and seals the crown, preventing chimney water leaks. CrownCoat works even better for crowns with smaller cracks and in slightly better condition. It’s easier to apply and it dries faster. Read more about chimney crown repair in our article “Chimney Crown Repair” or our video “Chimney Crown Repair”.

Chimney Flashing Leaks

 

chimney flashing leaks
Using FlashSeal to repair chimney flashing leaks

 

Chimney flashings are another potential source of water leaks. Where the chimney meets the roof line is a particular weak spot for water penetration because as rain water runs down the roof, it gathers and runs off right onto that joint.

Over time, as the chimney flashing deteriorates, water can gradually begin to seep into that joint and into your house, ruining drywall, causing wood rot and mold growth.

There’s a product called FlashSeal that you can apply on top of the chimney flashing to seal up this joint. There’s a mesh fabric to also apply underneath. This makes it even stronger.

Brick Chimney Leaks

brick chimney leaks
Use ChimneySaver water repellent to fix brick chimney leaks

 

The last problem area is the bricks and mortar joints. There are many different types of brick out there. The softer and more porous the brick, the more likely it’s going to leak. Mortar joints are another problem area. Many times, the mortar mix is has too much sand in it, causing it to soak up water like a sponge.

Also, many times the mortar joints are struck (packed in with a special tool) too shallow, causing water to be able to quickly absorb and pass through the thin layer of mortar. To prevent water penetration in brick and mortar joints, try a waterproofing product called ChimneySaver. It’s a breathable water repellent that you spray on your chimney with a pump-up sprayer. It actually forms a chemical bond with your masonry about 1/4″ below the surface, making the masonry repel water for 5-10 years.

If you have cracks in your mortar joints that are wide enough to stick a credit card in, you can use a product called CrackMagik. It fills in the cracks that are too large for the water repellent to fill. Most water repellents can fill hairline cracks. Any bigger cracks need to be filled either with a mortar crack chimney repair product such as CrackMagik, or for more severe cracks you will need to tuck point the mortar cracks with new mortar.

By protecting the chimney crown, flashing and brick and mortar, you’ll save yourself the expense of chimney water damage and eventual chimney replacement. Water damage causes over $1 Billion in damages every year. In most cases you can avoid this damage a little preventative maintenance once every 5-10 years.


Clay Lamb

Clay Lamb is a Cincinnati Chimney Sweep contractor and the executive producer of the YouTube channel, podcast, and blog Ask the Chimney Sweep. He is also an award-winning educator and public speaker in the chimney and fireplace industry.

AsktheChimneySweep.com….Educational Videos

AmChimney.com….American Chimney Cincinnati, OH

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Clay Lamb

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16 thoughts on “The Top 3 Ways to Solve Chimney Leaks

  1. Hello
    We have recently installed a wood stove insert and stainless steel liner. We feel our heat is continuing to be lost into the fireplace and chimney.
    Is it alright to insulate the rear of the woodstove insert? In addition is it alright to seal the stinless liner around the start of the chimney to prevent heat loss?
    Any expert advice would be greatly appreciated.
    Thanks
    Brad Watters

  2. Because I cannot see the whole picture of your situation, I would only recommend insulating the stainless steel pipe at the point where the damper is located with ceramic wool . I don’t feel insulating around the back of the stove would be of benefit to you. Also I personally would want the heat generated by the heating up of the fire brick to mass behind the wood stove for maximum heat
    Burn safe and warm
    Clay

  3. Hello. I recently had a chimney sweep crew come out for normal cleaning of my chimney. After they had cleaned, they informed me that my crown was damaged and water was leaking through into the inside of the house. I paid them in full for the chimney sweep and scheduled another time and day for them to return and repair the crown.

    On the day they returned, I watched as they brushed Crowncoat Brushable Sealant(they said this has a 15 year warranty) onto the crown, then sprayed some other sort of sealant around the chimney. That took them about 45 minutes to finish. I was floored when they told me it was $800. Does that seem like a HUGE number to you? I really don’t have any experience with this. Thanks.

  4. Please don’t tell me that you did not get a quote on the cost of this prior to the work being done. Our costing for us is always relative to the “degree of difficulty” and the amount of product used on a project such as yours! Two of my young, experienced, brave, ladder climbing and agile guys could do a lot of work in a short amount of time. That is if they were both working at the same time on the same project. This is an hour and a half of “ladder-work man-hours”. I just got a plumber’s bill for about the the same amount of “man-hours” for a job at my home. 🙁
    Clay

  5. When we bought our home 8 years ago, we were told there had been a roof leak, but it had been repaired. Unfortunately, that was not true. After 3 different roofers were unable to stop the leak by replacing the flashing and adding a copper collar, we called a chimney professional. He said it is the mortar on our chimney and sealed it with some very expensive sealant. It lasted about 3-4 years and started leaking again. He resealed at no charge, but it continues to leak. It leaks down both sides which causes water to seep through our bedroom ceilings and run down the walls. We do not want to spend the money to have the ceilings repaired over and over, we just want to stop the leak permanently!

  6. The roof repair may have been a sign of a failing shingle issue? Water testing on a dry day is the best way to confirm the flashing is still doing it’s job. Only soak the flashing and not the brick work. The water repellent may have stopped that problem, and another area is causing problem some 4 years later.
    In most cases, water problems don’t go away and then reappear in that spot.
    The returning chimney company 4 years later sounds to me like you selected a decent chimney contractor.Please check out all of our blogs and videos on water problems, water repellents and don’t call a roofer for a chimney problem and also Leaking Roof on Ask The Chimney Sweep.cpm
    Yes water problems are always a process of elimination. Also, may I suggest, journaling your attacks on this water problem and any other work that you do often the obvious solutions to your water problem will appear
    Best to you on resolving this water problem,
    Clay Lamb

  7. I have an exposed but unused chimney in a room of an old house. It has leaked a bit of sticky creosote. I would like to keep it for the Art Deco effect but don’t want to be trouble with the sap. Is there a way to seal it or should I know it out before redoing the room?

  8. That sap I believe your referring to is creosote.
    The question is, are you burning wood?
    I would recommend looking online for a member of the National Chimney Sweeps Guild, contact the http://www.NCSG.org site for a Chimney Sweep that could solve the issue of where and why the bricks are leaking this material.
    It sounds unsafe as well as unhealthy check out my videoChimney
    take a look at our video here that may help!
    Creosote Removal
    https://youtu.be/iaPkK3YDYsg

  9. We do not use our fireplace. Everytime it rains or the snow melts we have a flood in our basement. We have found that the water pours in from the clean-out in the basement. Is there a way to fill in the clean-out up with something to stop the water?

  10. Here is the way that I approach these types of water issues.
    You will first need to determine is the water coming down the chimney flue or not!
    You could check “during a rain” with a small mirror an flash light looking all of the way up the flue.
    Also consider that the water “may be” coming in at ground level from of the outside of the chimney.
    We often check this when it is warm and dry by soaking the ground around the outside chimney base, to see if we can introduce water at the lowest level and then working our way up the chimney. The next logical area for me would be the corbeling slope or hips located on the outside to the chimney shape, them move up to water testing the chimney flashing.(…..not some one saying the flashing is LOOKS fine).
    Think of it this way, could the water be coming in from the ground and not down the chimney flue?
    I do not feel that you can stop the water from the inside, by plugging it. To often it will just move the water to an another area of entry! Hydrostatic water pressure from the outside is often just way to powerful!
    Strange water is our friend as well as our enemy, be sure to document each step, the day, weather conditions, time, hours for water to percolate down into the ground. I have seen small foundation holes that were plugged -up during the original construction,that failed 30 years latter and now are allowing for gallons of water entry the home.
    Stay with it, and let me know.
    I hope this helps!
    Clay

  11. I just recently had a fieldstone chimney built this past summer. Along with it a new metal seemless roof. At the beginning of winter, I noticed water stains on the chimney below the roof line that would come and go with the rain and snow. I never saw any leaks during the summer and fall?
    I brought the roofer in to install a cricket to assure we were not getting buildup and leakage somehow thru his flashing. He could not find any areas where he deemed the problem a roof problem. He said that there was noticeable mortar stain post rain on the roof panels.
    Could this leakage be from mortor soaking water into the chimney? Why did it not happen all summer/ fall during heavy rains? My contractor said the chimney should have been sealed. My mason said he has never sealed a new chimney in his life? Help!!

  12. David,
    Big congratulations on your new addition, it sounds awesome. I’m far from being a scientist or even claiming to be the last voice on this issue. I will say that I was somewhat surprised to hear that a cricket was not installed during your original construction.
    When we work with stone, we personally think of it as being totally different than brick construction. But let’s remember stone construction has been around for thousands of years, but that does not dismiss the idea that they had water intrusion issue that needed to be addressed on those old castles walls.

    Let’s stop and talk about adhesion first, or what is called the bond or bonding of the dissimilar materials, that is required to prevent water penetration.
    Stone is much “less porous” than that of brick. Think of it this way, mortar is able to soak into the brick, where as mortar somewhat “incases” the stone, thus locking it into place. Because brick is so porous the adhesion is much greater. Again brick suck it in, where as mortar wraps around the stone. We always use a *liquid bonding additive when mixing our mortar materials (Acryl 60) as it promotes a much better adhesion.

    At this point here is my recommendation as to how we would approach this; “new construction or old”, “previously water sealed or not” I would recommend buying Chimney Savers Solvent base water repellent VOC.
    Following the Manufacture’s directions; (be sure to shake it up and Mix it well) spraying this liquid material from a garden type of sprayer, soaking it primarily in the mortar joints. For us we would be working from the lowest part of the stone chimney and then moving our way (UP) the chimney. Then using just a regular leaf blower, blow the wet surface some what dry. This “drives the solvent material deeper” into the masonry surface. Then we would apply another wet application or what many call a wet on wet application.
    Start by working in a smaller area, than as you get comfortable you will be able to expand your working area.

    *(Caution on covering the roof shingle, wood deck and glass windows)!!!!!!!!
    I’m not sure who is going to do this work, but this is rather time consuming, but not difficult for chimney contractors. You can find a reputable Chimney Sweep in your area by using this link to the National Chimney Sweep Guild locator: http://www.ncsg.org/search. Also be sure and go online and read their customer reviews from Google, BBB and AngiesList. I’m never impressed with those cheaper “Swab and Rob companies

    If you’re a (DIY) “do it yourselfers” *Chimney Savers Solvent based VOC, can be purchased in our e-store http://www.FireplaceandChimneySuppy.com

    “Remember finding water problems are always “a process of elimination”, so start with your least expenses options first!!!
    I’ll bet that you will whip this water problem!

    Here are (3) Ask The Chimney Sweep Videos
    https://youtu.be/hSY4ApHXLl4

    Chimney Leaks
    https://youtu.be/hNU-W7YmI5E

    Leaking Roof
    https://youtu.be/7djc7ayYJWs

    Hope this helps, “Stay Dry”
    . . . Clay Lamb

  13. We have an issue where water drips into our basement from the underside of the first floor fireplace. We have a brick chimney with two galvanized metal flues – one for the gas furnaces and hot water heaters in the basement and one for a fireplace insert on the first floor. Both flues have caps that appear in good condition. When it rains hard we get water dripping into the basement, apparently from between the chimney masonry and the two galvanized flues. In the basement the water drips down the wall, originating where the flue goes through a piece of plywood and up into the chimney. This is above grade level so I’m confident it’s not ground water or foundation issues. There is no sign at all of water in the fireplace on the first floor. At first we suspected the chimney crown because we knew it had some cracks in it. We hired a chimney repair company and they applied sealant that supposedly filled the cracks in the crown and also applied a layer of waterproofing across the caps’s entire surface. They also resealed all flashing joints and also the joints between the metal flues and the crown. Unfortunately we just had the first heavy rain since the repair and we got just as much water as before in the basement. So my question is obvious: what else should we check? Although the flue caps look OK could they somehow be letting water in? Other ideas? Thanks in advance.

  14. Chip, it sounds as you have done a great job of isolating this water problem so far. This is the way I would be moving forward, let’s call this (dry day water testing). Starting just above the ground level and using normal garden hose I would do a slow controlled heavy soaking of the chimney at the lowest logical entry level. I’m trying to get water (into) the house under very (dry conditions). Introducing controlled water soaking has often helped me discover the water point of entry. In other rooftop water soaking situation, I have done this. position one serviceman in the attic and the other on the rooftop with the garden hose, both communicating back and forth using walkie Talkie radios.
    So far we have not been able to discover the point of entry.
    Don’t forget there may be multiple points of water entry in your chimney.
    I hope this tip helps you in solving your water problem.
    Regards
    Clay Lamb

  15. Hello

    I have an issues where rainwater from the roof is dripping or sometimes pouring depending how hard it rains down the brick of the outside part of my chimney. This then leads to discoloration and algae growing on the brick. Plus I’m sure it is not to good for the brick either. I had my roof replaced last year. But I was wondering if there was something that could be added to divert the water.

    Thanks

  16. Good call, sir. I think you’ve answered your own question, you’ll want to get a roof diverter Their basically small pieces of metal that divert water down to the gutters, most often dripping over the edge and away from the chimney. Let me address brick real quick: bricks can act like a sponge and absorb water and when freeze-thaw comes it can break the brick surface. You’re absolutely right it can create brick damage. While also on the rooftop I would suggest using a higher-end water based water repellent not a sealant. Most often you’ll get about 100 sq. feet per galloon. we like to do a wet on wet light fogging when we’re doing it. Simple tip: if you spray the joints it keeps you in a logical pattern and the bricks will automatically the overspray.

    I recommend the 3 gallon size, I think it’s easiest to work with: http://amzn.to/2FSTQvq

    Videos for further information:
    https://youtu.be/T2vKULfVA4E
    https://youtu.be/hSY4ApHXLl4

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