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Cracked Concrete Chimeny

6K views 20 replies 8 participants last post by  Maintenance 6 
#1 ·
Here's some pictures of what I am trying to repair and I'm trying to find out if this is something I can do myself. Here are some pictures. As you can see there are a lot of small cracks as well as a large hole.
Does anyone have experience in fixing something like this?
How would I go about doing the repair myself? Where should I start? Is it better to hire a professional?
Thank you for any and all advice
S
 

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#2 ·
Is that an actual "chimney" as in for a fireplace? OR is it a covering for some type of vent coming from under the house? It appears to be stacked block construction with something like a skim coat of mortar over it and the outer coating has deteriorated over time. The "hole", as I see it, is where some of this outer covering has come off. I've seen this type covering on other structures. Have you tried to pull off any of this coating? I've seen it where you could find a starting place and pull off large hunks of it, as it didn't seem to bond very good. I'm not a masonry person, there are some on this forum who give great advice and hopefully they will chime in here. Right off hand I'm thinking that if the internal part of the structure is good, then a new outer covering may be all you need. With the height of that wall, and it looks good, I would be looking at something a little more decorative if needed. Good Luck, David
 
#3 · (Edited)
Not that it really matters, but where are you by the way? Could you update your profile to show this for your future posts? (If others reading this wouldn't mind it would be great too!) Those of us who try to help find it useful to know, especially if you are US, Canadian (the country we should have invaded instead of Iraq) or like from the English speaking countries with her majesties accents like the UK, New Zealand or Australia. Or wherever.

Anyhow, call a mason. It will be cheaper than doing this yourself. Or a nice one, and most are, will tell you how much you should attempt yourself and quickly remind you of your limits.

It looks like you have a fair amount of moisture getting into or seeping out of this thing all the way from ground level to over the roof or did you just photograph after a major rain storm? That is not good for concrete/mortar/stucco and whatever else you have. You may find you have to replace the entire structure?

I also don't see any footing under this structure? Strikes me rather iffy if that much concrete block, if that is what it is, is just sitting on the ground.

If it is working chimney for a wood stove or fireplace (weird it would have been allowed to have an exposed side attached to exterior framing) call a chimney expert. It's not worth a house fire trying to DIY to save $1,000 or whatever. And, depending on where you are, this strikes me as something that could require an inspection and signoff. You may not be able to get the sign-off if you DIY.

If it is just a decorative covering over a hot air vent or two for whatever reason, perhaps a retrofitted heating system on an antique home? I agree it could be made to look nicer or less conspicous.

Be careful.
 
#4 ·
Thanks guys. It is a cinder block structure coated in a thin concrete slim coat that encases a hot air vent stack. The structure looked perfectly fine when we purchased the home(here in NJ) 2years ago. It has obviously deteriorated as moisture entered into cracks we did not see at the time. I'm not looking for a quick fix so I'll most likely call a professional.
 
#5 ·
Hey, do click on your username and add your location so we remember where you are in the future. You don't have to put NJ if you don't want to admit it. Just type in "Home of the longest continuous burning tire fire" and we will figure it out. At least give us some clue though.
 
#6 ·
Is it possible that the roof is draining against the chimney?
I can see eaves-trough on the one picture and wonder if there is a cricket missing/never installed.
The cricket (or saddle?) will deflect most of the water away from the chimney so this doesn't happen any further.
 
#7 ·
Is it possible that the roof is draining against the chimney?
I can see eaves-trough on the one picture and wonder if there is a cricket missing/never installed.
The cricket (or saddle?) will deflect most of the water away from the chimney so this doesn't happen any further.

Finally, someone else that refers to it as a saddle! :thumbup:


I'd suggest having the chimney re-lined, make sure water isn't coming in at the roofline, patch the larger cracks & missing plaster, & paint the entire chimney with a product similar to Sherwan-Williams Loxon XP.
 
#8 ·
I am losing people here. I thought I heard this was just a vent stack of some sort and not a chimney? Why it is encased in such an elaborate thing that is falling apart is what escapes me? No matter I suppose, water is definitely getting into it from ground to above the roof. Worth repairing given the damage shown would be my question if the whole thing has hidden compromises? The whole thing could be rather flaky?

I say again, call a mason.
 
#10 ·
What does this vent? Chimney block were pretty common at one tine. A square block with a round hole through the center. They were not layed up with any kind of ceramic liner. They were usually set on a tab poured with the building footer. It appears that's what you have. When used as a chimney, the furnace kept them dried out pretty well. They are a little sketchy when used for a wood stove or fireplace, as the creosote/tar residue would build up inside them. Gas furnaces produce a lot of moisture, and the exhaust is also pretty corrosive and will attack the mortar joints from the inside. Any moisture that absorbs into the block, and cinder block are plenty porous, will be subject to freezing. That situation will blow off the parging on the outside, like your picture shows. The problem you have is that you can only repair the cracked joints on three sides, not the ones that face the sub-siding. Depending on what you use the chimney for, that could be a danger. Your best bet may be to repair the cracks and spalls and then have the thing lined. These block are no longer produced, for just that reason.
 
#11 ·
What does this vent? Chimney block were pretty common at one tine. A square block with a round hole through the center. They were not layed up with any kind of ceramic liner. They were usually set on a tab poured with the building footer. It appears that's what you have. When used as a chimney, the furnace kept them dried out pretty well. They are a little sketchy when used for a wood stove or fireplace, as the creosote/tar residue would build up inside them. Gas furnaces produce a lot of moisture, and the exhaust is also pretty corrosive and will attack the mortar joints from the inside. Any moisture that absorbs into the block, and cinder block are plenty porous, will be subject to freezing. That situation will blow off the parging on the outside, like your picture shows. The problem you have is that you can only repair the cracked joints on three sides, not the ones that face the sub-siding. Depending on what you use the chimney for, that could be a danger. Your best bet may be to repair the cracks and spalls and then have the thing lined. These block are no longer produced, for just that reason.

Thanks for elaborating that point, that's exactly my thoughts. :thumbup:

Usually plain mortar was layed between the flue tiles (which I'm only assuming are actually inside) which resulted in such a thin joint that it eventually failed. Sometimes they would have used air-set refractory cement instead, which is the same material used inside of fireboxes. We now know years later that air-sets don't stand up to water/steam/vapor well at all. Often times, chimneys that held up to dry wood venting start to fail quickly when subjected to the cyclic, moist venting from gas furnaces. That shouldn't be too bad to have re-lined as you won't need the crazy-expensive bendable stainless liner.
 
#15 ·
Very interesting system there Stu. I've never seen that before. As Europeons, I think you have far more faith in older, proven technology, such as good old masonry construction. Here, people seem far more concerned with the speed & price, not so much longevity.

BTW, what would you venture to guess that mix of perlite to portland is? 6:1?
 
#18 ·
When we build a chimney now gap between the clay liners and the brickwork of the chimney is filled with vermiculite, mixed about 8 or 10 to 1 with portland to stabalise the mix. We used to fill the gap with sand/cement mortar, but now it needs to be insulated. Before 1965 most chimneys were built without liners and the flue was just parged with sand/cement.
 
#19 ·
There are very few perlite or lightweight flue liners used in the U.S. A common use of perlite is between the clay flue or a tin flue and the chimney block.

The saddle flashing is common in older structures with a chimney at the center of the house and really does not apply to a chimney laid on a roof with one side obstructing the runoff. If it too wide, a cricket is used to divert the water around the chimney.

It is difficult to give any reasonable answers beyond guesses since there is little real fact given like the type of vent/flue and what is is made from. My assumption is that it is some kind of a tin chimney (single or multiple walls), but not a clay flue since no legal flue could be used in a chimney block that size and still be legal unless the exterior of the chimney flue has a very, very small diamater. The dark stuff behind the skim coat could be creosote deposits that are very corrosive to concrete, mortar and skim coats. The source of the moisture is probably from above and that is probably the cause of the cracks that will open/continue after coating and the process will continue to deteriorate. It is also possible the home is older and block is larger and the "temporary" vinyl siding hiding the real size of the flue.

Getting up on roof and looking at the crown/cap would tell a lot.

Dick
 
#21 ·
I would venture a guess that there is no liner. The block are square with about a 10" round bore. When they are layed up, the round bore becomes the flue. That is what made them a problem. A cracked joint would be open directly to the structure of the building. Insurance companies, as I understand it, had them banned, but they were still available in 1970, as my garage has a chimney built from them.
 
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