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Jack 10
Joined: 04 Jul 2007
Posts: 3
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 Posted: Wed Jul 04, 2007 11:36 am Post subject: Chimney Design ? |
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I am a New member from Canada , where my education history includes Architectural technology college diploma decades ago.
So much has changed especially in regard to water vapour control.
So I am lost in regards to the problem I am up against.
My 1981 high rise bungalow has a large brick chimney from the Basement family room zero clearance wood fireplace, to the roof, it contains the typical 8 x 8 clay chimney liner up to the 3 inch concrete capped and sloped Chimney top and typical 12 x 12 metal raincap.
From 1990 to 2000 noticed no particular brick spalling (flaking) at the top of the chimney.
In 2000 We had a gas fireplace insert installed inside the existing zero clearance fireplace. So they run 5 inch stainless steel pipe up the 8 x8 clay pipe up to a new raincap at the top.
(I believe they also wedge the zero clearance fireplace damper open permanently to run this pipe up. They also aluminum capped the roof exit of the 8 x 8 clay tile around the 5 inch pipe
Now 3 or 4 years later serious spalling/flaking of brick started where each spring I literally sweep the roof off
I have made attempts of figuring the cause out, at first assumed it was leaking concrete cap, because it had minor cracks , but sealing that did not work. I tried removing a brick near roof level and replacing it with a vent . (I suspected water vapour might be exiting up chimney on outside of 5 inch pipe due to wedged open damper from old fireplace ) But that has not slowed down the brick deterioration either.
Any thoughts ? before a complete brick chimney rebuild ? |
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birgco
Joined: 01 May 2007
Posts: 302
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| Posted: Wed Jul 04, 2007 1:38 pm Post subject: chimney design |
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| I'll take a crack at it (no pun intended). It appears that the problem started when the 5 " ss pipe was installed inside the 8x8 clay flue pipe of the chimney. One possible explanation (assuming as you noted the cap and mortar joints are tight) is that now the chimney is drawing moist heated air from the house without having the ventilation or adequate heat to keep the upper part of the inside of the chimney warm enough to prevent surface condensation from occurring. By wedging the damper permanently open, it seems likely that a constant flow of moist air is now moving up the chimney. Also the new cap might be restricting or preventing the moist air from escaping as it would have previously. Rather than rebuilding the entire chimney, I would first have the space around the ss pipe filled with a light weight cement/concrete that is specially made for this purpose. (sounds like this step was omitted by the flue installers). This will also help to greatly strengthen the entire chimney structure and provide some much needed insulation. Next, nail wire lath to the exterior of the chimney bricks (providing the bricks aren't too badly deteriorated) and apply 3 coats of stucco. Obviously, this is only a good idea if you would now like a stucco exterior for the chimney. Also its probably a good time to check the step and counter flashing around the base of the chimney before the stucco work is completed. Hope this helps. |
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Jack 10
Joined: 04 Jul 2007
Posts: 3
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| Posted: Thu Jul 05, 2007 4:49 am Post subject: |
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Thank you Birgco.......... you have added weight to my origninal suspicions. I also like the stucco idea, I was considering attaching strapping and then attaching a cement board product. But your method keeps the added thickness down and easily within the overhang of the concrete cap drip.
I also typically try to check the sources of advice like yours so reviewed your 46 posts.........I liked what I saw , the added sense of humour is also a bonus .
jack
Sault Ste Marie Canada |
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phansford
Joined: 18 Apr 2004
Posts: 531
Location: SW Ohio
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| Posted: Thu Jul 05, 2007 5:46 am Post subject: |
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Birgco theory is one possible explaination. We see similar problems, but with efflorescence, typically after a new high efficiency furnace has been installed and the Owner does not want to pay for a new flue to be pulled thru the older (and larger) flue. The houses in my neighborhood have masonry fireplaces with the flue for the furnace and the water heater sharing the chimney.
I suggest you contact the local brick supplier and ask for someone with the technical knowledge to review and answer your questions. Or even an HVAC contractor.
Professionally, I would not leave the old bricks in place and stucco over the problem. Now you are just concealling the problem. It is better to have visually control over such matters. Removing a few courses for brick and replacing them, or even replacing only the damaged ones is not a great cost and probably cheaper than stucco. Brick is a natural material and typically can be matched either exactly or very closely. |
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Dakota
Joined: 05 Jul 2007
Posts: 2
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| Posted: Thu Jul 05, 2007 6:22 am Post subject: |
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Agree also with phansford. Have encountered witnessed simmilar problems in the recent past. The brick quality was questionable and started to deteriorate due to prolonged moist. We took care of the moist and could succesfilly cover the brickwork with new exterior finish. If the moist problem is not taken care of the brick will continue to detariorate.
All the best. |
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Dakota
Joined: 05 Jul 2007
Posts: 2
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| Posted: Thu Jul 05, 2007 6:23 am Post subject: |
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Agree also with phansford. Have encountered witnessed simmilar problems in the recent past. The brick quality was questionable and started to deteriorate due to prolonged moist. We took care of the moist and could succesfilly cover the brickwork with new exterior finish. If the moist problem is not taken care of the brick will continue to detariorate.
All the best. |
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JWmHarmon
Joined: 15 Apr 2004
Posts: 111
Location: Ohio
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| Posted: Thu Jul 05, 2007 8:59 pm Post subject: Concrete cap - brick mortar joints problem |
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Another possibility for the entrance of moisture into the brick is the joint between the concrete cap and the brick. The cap may be sealed properly with all the cracks caulked, but that still does not solve the problem of the mortar joint between the cap and the brick.
The same problem can arise on brick buildings with stone or concrete cap stones. These are often caulked with flexible caulkng. Over a period of years the caulking deteriorates from ultraviolet rays from the sun. Where it separates from the brick or stone it creates a place for water to penetrate the wall.
If the mortar joint on the chimney cap has cracked, the crack may be small and hard to detect, but is still suffiecient for water penetration, leading to efflorescence and spalling.
Does the concrete cap have any overhang? If so, does it have a drip cut into the underside of it? If not the rain water may run horizontally back across the bottom of the cap to the brick and leak through small mortar joint cracks. Even the smallest almost invisible crack can be enough to allow water to penetrate.
It is better to solve the problem rather than covering it up. If neglected, this problem continues to get worse every year until the entire chimney needs to be replaced. At some point the brick deteriorates to the degree that the chimney may become unstable. The brick may seem to be intact on the outside surface, but inside it may be crumbling from repeated freeze/thaw cycles.
This can become a life threatening probem if the chimney were to collapse. Peple have been killed from falling bricks and stones from deteriorating buildings that have not been maintained properly.
If you have just started to notice it, then you might be able to remove the cap and a few rows of brick and replace only the top portion. You may also find that the damage goes down more layers of brick on the inside than is visible on the outside. The only way to know is to have a mason start removing brick until you find undamaged brick. Then it can be built up again from that point.
You may also find that the flue is cracked and needs to be replaced. This may not be visible from the outside, or from the inside if you take the metal cap off. It may only become visible when you remove several layers of the brick.
From a design standpoint, it may be desirable to remove the face brick down to the roof level before building the chimney up again.
I completed a project like this a couple of years ago and have one waiting for me to do before winter. I have another project at a local brick building with capstones with the deteriorating caulk problem. This building has moisture problems on the interior plaster walls and newer drywall from the leaking joint between the brick and the cap stones.
If the problem is not yet severe, you may want to try having a mason grind out the mortar joint between the cap and the brick and tuck point it carefully. This may be enough to correct the problem.
I would also suggest replacing or adding and additional thin layer of concrete over the present cap if you decide to keep it, since caulking cracks in the cap is only a temporary solution.
_________________
When building or manufacturing always ask, "How will we recycle that?" - JWmHarmon |
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Jack 10
Joined: 04 Jul 2007
Posts: 3
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| Posted: Fri Jul 06, 2007 4:47 am Post subject: |
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Many interesting points JWmHarmon.
I skim coated the Concrete cap three years ago, it eventually spalled of so went with a foundation coating, did caulk also , but I am going to reinvestigate again. I still don't trust that the gas company when they installed the fireplace did not consider the impact of having a 10 inch damper held open around a 5 inch pipe, leaving lots of room for moisture from rec room to attmept to rise up outside of liner to a deadend at top of flue.
Seeing the complications brought up here , I am going to pay a Chimney Sweep /Consultant for an hour of his time to review my options.
I might even look at option to change back to wood (I have lots of land access to wood now) Even if it means taking cap off and removing one or two lengths of 8 x 8 clay tile that I suspect cracked too with winters ( winters that go to -20 F for multiple days) Tnen rebuild 2 or three feet of chimney. I think I am handy enough to do that myself, the hard part might be getting concrete cap off without breaking (yes it has 2 inch overhang and groove for drip)
Thanks to all for proffessional advice ! (its as serious as I was worried it might be ! ) |
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