Interior masonry chimney, cracks, wall clearance questions UPDATE WITH PICS

[Highbeam]

I have a single story home with a centrally located masonry fireplace filled with a Lopi insert and a full SS liner through the clay lined flue. The chimney used to be in the garage which was converted to living space so the old garage slab is still in place with carpet on it. Walls were built around the plain concrete "back" of the chimney into the converted garage at about a one foot offset leaving an empty wasted space for junk to accumulate from the attic above. The roof trusswork is tight against the masonry and insulation touches the concrete. The house is 40 years old and new to me.

I just replaced my electrical panel, Zinsco deathtrap, and had one of the walls open to clean out the junk and to inspect the concrete fireplace. I discovered a vertical crack at the rear corner that begins about a foot from the ground and runs up the chimney to about 7 feet above the ground. The width shrinks to zero at the bottom and zero at the top and is about 3/16" at its widest. No creosote or water evidence. The crack makes it through the transition from wide firebox to skinny single flue chimney stack. I could not inspect the other rear corner for similar crackage.

I have a few questions. I will be rebuilding the aesthetic walls surrounding the rear and sides of the old fireplace. Can I reduce or eliminate the 12" offset?

I want to insulate all around the attic penetration which means sheetrocking up to the chimney. This seals off the lower chimney and firebox to the ground, is that okay or do I need to insulate and seal the aesthetic walls and make a chimney chimney?

How big a deal is the crack? Can I repair it, and if so, how and with what.

I had been burning the stove all day with no blower to stay warm while replacing the panel and the only warm spot on the chimney was at the transition from skinny chimney to wide firebox. It was only warm, just noticable compared to the rest of the chimney. No ash drawer or cleanout.

I can get some photos tonight if it would be helpful. I hope to seal off the attic tonight.

Thanks

 

[kevinmoelk]

A picture says a thousand words.

Zinsco panels aren't the death traps people think they are, they do have a terrible reputation. They were used all over WA state. Biggest problem with them is that there was almost no room for expansion, their layout was poor, and since they're no longer made a new 15amp breaker costs you $60 bucks. Safety wise, they aren't bad if wired correctly. That said, an upgrade to a Siemens or SquareD panel is a big step up.

-Kevin

 

[Highbeam]

Thanks for replying, I set in a siemens panel that is a combination transfer switch approved by the UL with the little lockout plate. Lots more expansion room and the crackling breakers are now off of my mind. I disassemled the old panel enough to see where the buss bars had been arcing for a long time. Even found an old arced out breaker sitting on top of the panel.

I have a panel full of relatively good used breakers if there is a market.

I will surely post some photos tonight but I am going to look for some masonry crack sealers in the meantime since nomatter what the verdict is, the crack must be closed up.

 

[Highbeam]

UPDATE WITH PICS

I went and took some photos so maybe you folks could help me out. The crack measures 1/8" at its largest and by feel another crack seems to be present in the exact same spot on the other side, I can barely slip an arm over there. The one block was easily removed by hand and the rest are tight.

I purchased some cement based crack filler but did not use it yet. To be honest I am a little afraid that the back wall wants to fall over which would be a problem since the fire is lit. My level shows the back wall pretty much plumb.

Please let me know your opinions.

 

[Highbeam]

One more pic of the front with the Lopi crankin at full power. The hearth is 4" thick Wilkeson Sandstone. The pic is a little dark but should due.

 

[kevinmoelk]

Looks like a foundation problem that is causing the chimney to crack. Better have Elk take a look and give his opinion. Not sure how much this will effect the functionality of the stove seeing as you have a liner.

-Kevin

 

[elkimmeg]

Boy that 3 picture concerns me with the 2/8 appears to be making contact with the block right below a structual crack
The crack is too uniform following almost exactly the 4" thickness. I bet it cracked right into the fire box?

I'm going to add to this post in edit mode after I look at those pictures again..

More alarming and I suspected this holllow core blocks were used look at the side of picture 2

No wonder they cracked so easilly..

Code requires 4" solid masonry units not having your fire box lined and protected by hollow core blocks It also appears th have clearance to combustiables issues
2" space between solid masonry to any combustiable framing members I don't know what code is to hollow core blocks because they are not susposed to be used
If I am looking at that chimney from a garage then where id the 5/8" fire code sheet rock providing one hour protection to the living space?
Even if the home was built in the 60's living space protection was required then.

So what could cause the problem? the mason installed the fireplace on only the garage slab and did not do an adequate footing. That is one possibility.

The other one was an intense chimney fire hot so hot the blocks expanded and cracked possibly way too hot of a fire in that fire box litterly. blew the back wall out.

So how was the fire box before that insert installed? what about the flue liners?

I will wait for your answers but you have a damn good reason to be concerned.

 

[Highbeam]

The house was built in 1967 by a cabinetmaker.

I couldn't help myself and filled the one crack last night, also rebuttered and installed that loose block to seal it all up. The insides of the cracks were clean but I wanted to seal it all up just in case. I understand that the repair isn't 4" deep. Oh a little more information, the firebox (the interior trapezoid part) extends all the way down below the garage slab grade onto a footing in the crawlspace. Looking down into the void between the outside of the chimney and the firebox I could see all the way down. I don't think that the chimney is set on the garage slab but I can't be sure. Also, looking down into the area between the firebox and the exterior block wall I couldn't see much of a crack at all, not certain if it made it into the firebox.

The blocks were indeed hollow but every one that was visible was mostly filled with mortar. The outside sure looked nice though (trying to find some humor).

The photos are taken from the converted garage. There is now living space all around the chimney so the insulation will be removed in an effort to improve heat to flow. The conversion was done with permits in about 1974. While there looks to be sheetrock between the hearth wall and the chimney, there certainly is none on the other three faces, just this big 12" gap and then wood. The upper framing members are actually touching the chimney as you noted, I actually thought maybe for support.

There are no apparent cracks on the converted garage slab around the chimney base. We did have a moderate earthquake several years ago and I am certain that there was at least one chimney fire.

The firebox was in decent shape when I had the insert out for the liner installation a few weeks back. The firebrick's mortar on the smokeshelf side was mostly washed out near the top due to a missing raincap. The firebox was black from old fireplace fires and no obvious cracks jumped out at the installer. We removed the steel damper during the liner install. The clay liners were 8x12" and took the 6" flex very well, the sweep thought everything was in good shape and passed "chimney" approval before the liner install. The SS liner was done because I wanted a safety and performance upgrade and to make sweeping easier.

I really do appreciate everyone's input. I am not a mason nor a chimney professional but I hope to learn as much as I can about the right way to deal with this.

 

[Highbeam]

I see no reason that the stove won't perform flawlessly except for that one time that the whole mess falls over. Hah!

 

[kevinmoelk]

How big a deal is the crack? Can I repair it, and if so, how and with what.


I see no reason that the stove won't perform flawlessly except for that one time that the whole mess falls over. Hah!

More pictures would help beyond your descriptions. Sounds like a proper footing may have been made, but who knows. If the job were permitted, it may be worthwhile to look it up to see if any notes were made concerning the chimney.

You have a crawlspace under your garage? Or am I reading that wrong?

No offense Highbeam, but why did you ask the question if you already knew that you were just going to fill the crack?

You got an answer from a man with a wealth of knowledge and experience who expressed his concerns and then simply chose to ignore his advice? I don't get it.

And since there may indeed be a chance that the "whole mess falls over" I would not see such a remark as funny. Now is the time to correct the problem, not just patch it over and keep your fingers crossed. This is fire we're talking about.


-Kevin

 

[Rob From Wisconsin]

Correct me if I'm wrong, but aren't most garage slabs
somewhat sloped to promote water drainage??
So is it possible that there may be as much as a 1/2"
difference from front to back or corner/corner??

Rob

 

[Highbeam]

Maybe I wasn't clear. I patched over the cracks to prevent air/exhaust/carbon monoxide/ or anything else from leaking out while we looked into this further. The patch is only to minimize cooler gas movement and not a solution. I need to have priorities and the first one is waking up in the morning to be able to solve this problem.

The advice I have received from Elk was partial as he stated he would get back to me after I answered his questions. I answered each one and hope he gets a chance to reply soon.

The original house, all but the garage, sits atop a crawlspace on a footing/stemwall foundation. The hearth appears to be substantially supported by a footing that is all the way on the crawlspace floor. The chimney and house foundation was then backfilled and then the garage slab looks to be poured around the chimney as can be evidenced by the splatter of concrete on the lower course of block on the back three sides of the chimney.

Please be specific on additional photos that would be helpful. I will gladly do what I can to help you help me. I have no intention of "just" filling the crack. No advice was ignored but quite the opposite - I am eagerly awaiting more input. Raking it in.

I talked to a trusted builder today who referred me to a chimney sweep/retailer/builder type outfit as a local source of advice. I would like to be as informed as possible when that guy comes and looks.

Thanks

 

[Highbeam]

Correct me if I'm wrong, but aren't most garage slabs
somewhat sloped to promote water drainage??
So is it possible that there may be as much as a 1/2"
difference from front to back or corner/corner??

Rob

If this 40YO chimney were poured atop a sloped slab (I don't think it was) then the mason would adjust the gaps to make up for the slope I would think. The garage was a large two car garage but with only one door at the far end. More of a workshop since this guy was/is a cabinetmaker. I set a level on the back wall and it is relatively plumb. The joint work looks quite good too.

Yes the slab is sloped away from the chimney.

 

[Rhone]

I think it once being a garage is your answer. A house designed with a chimney, under said chimney is a 12"+ thick footer that extends 12-16" beyond the base with 5/8" rebar placed every 3" vertically and spaced every 16". Chimneys have one hell of a footer to support one hell of the weight of the chimney and prevent the weight & mass from shifting/moving and causing the chimney to crack. If this was a chimney added to a garage floor after the fact where there's just the normal thickness of concrete to support a cars weight thats probably your answer. I can't tell you if it's safe or not or what the future holds but my guess is they didn't rip up the garage floor under the chimney to put a proper footer and you're seeing the results.

 

[kevinmoelk]

Maybe I wasn't clear. I patched over the cracks to prevent air/exhaust/carbon monoxide/ or anything else from leaking out while we looked into this further. The patch is only to minimize cooler gas movement and not a solution. I need to have priorities and the first one is waking up in the morning to be able to solve this problem.

The advice I have received from Elk was partial as he stated he would get back to me after I answered his questions. I answered each one and hope he gets a chance to reply soon.

The original house, all but the garage, sits atop a crawlspace on a footing/stemwall foundation. The hearth appears to be substantially supported by a footing that is all the way on the crawlspace floor. The chimney and house foundation was then backfilled and then the garage slab looks to be poured around the chimney as can be evidenced by the splatter of concrete on the lower course of block on the back three sides of the chimney.

Please be specific on additional photos that would be helpful. I will gladly do what I can to help you help me. I have no intention of "just" filling the crack. No advice was ignored but quite the opposite - I am eagerly awaiting more input. Raking it in.

I talked to a trusted builder today who referred me to a chimney sweep/retailer/builder type outfit as a local source of advice. I would like to be as informed as possible when that guy comes and looks.

Thanks

Okay...good. Thanks for the clarification. No animosity towards you Sir, just making sure we are all on the same page concerning safety.

See bold above.... This seems to be a contradiction. How can the garage not have a crawlspace, yet the chimney footer be dug to meet the crawlspace floor? My only thought here is perhaps the garage maybe had a gravel floor prior to being finished? Or did the garage always have that nice mantle? That would be something... a fireplace for your cars, lol.

As far as pictures are concerned... the more the better. Just let everyone know what we are looking at. Can you get a photo of why you believe there is a footer in place? Pictures, pictures, pictures.

-Kevin

 

[Highbeam]

Thanks for sticking with me...

Imagine the house built without the garage. A stand alone house with an exterior chimney. The hearth faces towards the main living space. The footing for the home's stem wall is level with the footing of the chimney. You build the stemwall and the chimney and then backfill the exterior of the whole mess to grade. The crawlspace is not backfilled and is essentially a pit. Then you decide to add an attached garage to the same wall as the chimney. No reason to dig down and pour your slab below grade, you want the slab at grade so you can drive in and not have stairs. The garage portion of the home is built as a slab on grade structure and the original home is built with a crawlspace.

The photos of the concrete block work are taken from the garage side and the hearth photo is taken from the crawlspace side. If my hunch is correct, the blockwork extends below the garage slab to the level of the footing in the crawlspace.

I'm Mr. Mom tonight but I will do my best to make time to crawl into the crawlspace and investigate the footing. I hope to have some photos to show. There are spiders down there.

Thank you for sticking with me folks, I knew that it would be hard to describe.

 

[elkimmeg]

Here what has to be done all the bond blocks that are cracked have to be removed. They are the cement blocks that tie the cracked wall into the side wall.
Once removed they have to be motared in. I would use solid blocks for replacements. Before replacing, in the bottom motar joint ,I would imbed a wall tie crossing
the crack motar join below. The wall tie will act as metal re enforcement and create a better bond an lessen the chance of it cracking again. With a grinder and concerte balde, remove the remaining s motar in the cracked joint Simple caulk will not sufice you might use concrete or motar patch in a caulking gun to force as mush morar in there as possible.

Sir I do not know you skill level but the job scope may be beyond it. But at least you know know a way to repair it if hiring a mason.

I gave two possible causes, an earthquake could also be responsible.

 

[kevinmoelk]

Elk, I'm going to try and re-phrase what you said. Correct me if I'm wrong in understanding what you stated.

1-Tear out the back side of the chimney area
2-Use solid blocks
3-Rebuild the back side with the blocks and tie in with wall tie (which are basically strips of metal that go inbetween the mortar joints)
4-To add the ties you'll need to grind into the existing wall at the appropriate height of the mortar joints created by the new solid blocks
5-The first row or base row should be tied into the floor

I'll also add that when tying new concrete to old there are special additives added to concrete to help bond. It will help to spray down the old concrete to bring up the moisture level too. In that way the drying process will be slowed down and less likely to hairline crack. In fact, it's a good idea to keep the concrete moist and covered with plastic or wet burlap for a few days after the work is done to give the mortar time to cure slowly.

How did I do Elk?

-Kevin

 

[elkimmeg]

Elk, I'm going to try and re-phrase what you said. Correct me if I'm wrong in understanding what you stated.

1-Tear out the back side of the chimney area Remove only the bond blocks the entire wall does not have to be removed
2-Use solid blocks
3-Rebuild the back side with the blocks and tie in with wall tie (which are basically strips of metal that go inbetween the mortar joints)
4-To add the ties you'll need to grind into the existing wall at the appropriate height of the mortar joints created by the new solid blocks
5-The first row or base row should be tied into the floor

I'll also add that when tying new concrete to old there are special additives added to concrete to help bond. It will help to spray down the old concrete to bring up the moisture level too. In that way the drying process will be slowed down and less likely to hairline crack. In fact, it's a good idea to keep the concrete moist and covered with plastic or wet burlap for a few days after the work is done to give the mortar time to cure slowly.

How did I do Elk? Over kill you only have to grind out the split motar joint and wall ties in ther are useless unslee imbeded in the motar joint and simple grinding a joint will not alloe=w them to be embeaded. One could rebuild the back cornor but I think particial rebuilding can accomplish the same thing. One could get into it and decide that is the best path to go

-Kevin

 

[kevinmoelk]

Okay, I understand now. 2nd attempt: You would remove and replace on the bricks that span over the crack, right? Then before you add mortar you could lay down a wall tie to span the crack where the crack is at the joint itself. Then get one of those pastry chef mortar bags and squeeze as much mortar you can get in the crack and point up the brick.

I was confused previously about the wall ties, my thought was that you could use some of that special adhesive to glue in the wall ties into the old work after grinding the space for them. But now things are making more sense.

-Kevin

 

[Highbeam]

I took a pic from below in the crawlspace. Only real thing learned from below is that there are blocks all the way down. So the chimney is not resting on the garage slab. The hearth face of the chimney extends to the foundation in place of the stem wall in that section. Then the little step in front of the firebox is constructed into the crawlspace. Its supported by a footing that sits into the crawlspace. The little hearth step footing is what was pictured since that's really all I could see from below.

I don't quite understand the wall ties. I understand removing the broken bond blocks and removing the mortar joints where cracked and as needed to replace the broken blocks and remortar. Where do the ties go? Do they actually tie to the wall or jsut act to reinforce the location of the previous crack?

The crack extends up into the actual chimney a slight bit. Are those bond blocks replaceable without taking down the whole chimney? The price of this repair will be balanced against chimney removal. At this point, I'll assume the repair price is reasonable.

I will not be doing this myself. I would not feel safe or qualified but once done I want to deal with the walls. Does there need to be sheetrock on the chimney side of any walls? How far away must these walls be? And finally, may I close off the attic penetration or must the vertical extension of the large firebox portion of the chimney extend into the attic?

I thank you folks for such a non wishy-washy set of directions and advice. On one hand I am happy to hear that there is a solution short of demolition and on the other hand the repairs sound like a lot of work.

Here's the pic for reference. It is basicly an exterior chimney with the inboard part of the footing shared with the house. I was looking for an ash drawer but it is probably under the slab. I also threw in a pic of the new siemens panel with the handy UL tranfer interlock device. If it hadn't been for this panel change out I would have never seen the crack.

I am listening carefully and if you good people can add to the advice given please don't hesitate.

 

[Highbeam]

I think the lightbulb went on with the wall ties. They will just be buried in the new mortar across the old crack. Now to replace the broken blocks you must remove all of the old mortar on the three sides right? Then grind out and replace the mortar joint where the original crack simply followed the mortar joint.

Is that right?

Next is to pull apart the other wall and check that crack out. I think it is not as bad but I, and the mason, will need to know.

 

[Highbeam]

Allrighty then, I grabbed a 2003 IRC and the minimum air space clearance to combustibles is 2" for an interior chimney. Then where a chimney passes through a ceiling I am required to provide fireblocking of "non-combustible" material fastened in place.

Sheet rock is combustible, how about insulation with the paper removed? I'm on a hunt now.

The mason has been called and I am waiting on his schedule for a visit. The good fireplace shops are booked up and they referred me straight to their mason, must be their busy time of year.

On edit: The chimney, front, and sides of the fireplace require 2" clearance but the rear of the fireplace requires 4".

 

[elkimmeg]

this is an existing situation where all can not be corrected the hollow block issue still stands code requires 4 " soild masonry and 2" to combustiables framing menbers
passing threw a wall or ceiling requires 2" clearance to framing menber and that the be fire stopped with non combustiable materials Most embed sheet metal of alumium flashing as the fire stop in the nearest motar joint. this could be accomplished by grinding out the nearest motar joint installing sheet metal and cementing it in plus nailing it to the framing menbers helps hold it in place. The wall ties are as you figured in the bond block motar joints. this is not code but added protection preventing further movement and cracking all bets are off witha above average earth quake but the could be the difference. Me I would do it that way. People here have called me anal because I believe if doing something and there is a simple way to improve a situation I will do it or suggest it. To me I have been doing things this way all my life. I'm not a mason but could do that job. The most important thing is to provide or make up, the lost bond strength the cracking did, to that outer wall

 

[kevinmoelk]

Highbeam, on the first picture on post #20 in the upper right... Is that cresote coming through the bottom edge?

-Kevin