# Masonry Fireplace Cracking



## JBM (Mar 31, 2011)

The fireplace is causing heaving when it gets hot. You really need to take into consideration expansion on exterior chimneys. 

How was the firebox filled?


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## JBM (Mar 31, 2011)

Its not settling.


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## NickCat11 (Nov 8, 2015)

It was filled with block and concrete.


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## JBM (Mar 31, 2011)

Fireboxes should be filled loosely, or with 1/2 inch airspace to the outside wall. Above the firebox needs to be built with expansion aND contraction in mind


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## superseal (Feb 4, 2009)

Surely I don't like that firebrick size or the fact they're adhered to the block. The lick'em stick'em is a thorn too. You need to isolate the veneer to the block and the firebox construction as well. 

The hearth stone and mantle may make it in one piece if all the details are in place but two stones may be better in this situation...either a sacrificial mortar joint or soft joint in the center.

A true 4/6" stone veneer or maybe a brick veneer with air space and a traditional firebox and I doubt your looking at those problems.


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## NickCat11 (Nov 8, 2015)

The bluestone hearth and top rim bluestone that cracked are perfectly level. Top piece of bluestone baffles me because I can't see the heat of the fire getting to it.


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## dom-mas (Nov 26, 2011)

The entire unit is getting super saturated with heat because the firebrick are attached to the firebox with no air space. Chimneys deteriorate a lot quicker when there is no space between the flueliner and the surrounding masonry. Thermal bridging should be avoided in fireplaces big time


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## fjn (Aug 17, 2011)

NickCat11;

This problem is not the end of the world. Since the level on the hearth stone reads good and there is no rocking or change of plane,I would say you are safe to rule out settling / foundation concerns. Since you said it is your fireplace here are some recommendations that may help.While the hearth stone crack is not really dead center,however it appears quite straight. Possibly,you can measure equidistant on left side and saw cut a joint there also. In essence,you will then have a three piece hearth,at least the random crack will not be glaringly obvious.Then get some type of cap to prevent water intrusion down the stack. Lastly,you may have to resign yourself to have to do a little pointing more often than optimal. Again,it is not the end of the world. The next ones pay more attention to thermal expansion and you should be just fine.:thumbsup:


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## NickCat11 (Nov 8, 2015)

FJN,

Thanks again for your feedback. One other question, do you think I should rip out the splits and put full fire brick in instead? I know it's a lot of extra work but if it saves me some hassle in the future I'll probably do it before we get busy again in the Spring. 

This was the first all masonry fireplace we have done. Typically we build everything out of stacked stone and keep block work to a minimum. I figured my house was the best place to start before I add it to our arsenal of services. There were additional aspects to the project (pics below) which worked out well. Unfortunately there is one kink in the rope right now that needs fixed but at least it's a good learning experience


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## fjn (Aug 17, 2011)

Since what you have going on is probably multi faceted I.E. no expansion provided at firebox along with chimney / flue I don't know how pronounced a firebox fix will alleviate the problem.


Possibly,just possibly all the cracking you have going on is all that will happen. Keep your fingers and toes crossed,keep an eye on it and see how things play out before ripping the firebox apart. You may just get lucky with a band aid approach. You can always do a full blown fix at a later date.


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## brickhook (May 8, 2012)

I always suggest when firing a new fireplace, to build small fires to start with.

A very hot fire in a new fire place will certainly cause damage.

We built our cabin in '93. We were cleaning up and i was throwing all of the T&G scraps in fire. The fire got really hot, and when I looked up...The whole chimney had a 3/16" crack all the way across the 8' wide chimney!

I stood in the front door when I told my Dad ( in case I had to run) And he told me to let the fire go out, it would be ok.

To this day , you cant see the crack. It went back together. Lesson learned.

You may not have any further damage, just build small fires in it for a little while longer.


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## dom-mas (Nov 26, 2011)

Personally I would replace the splits with full sized firebrick, I think it's accelerating the problems. That one picture of the stone with the iron staining really suggests a water problem to me as well (take a look at the firebrick in that photo)...deal with that first The unit gets soaked, then gets hot and cracks. I'm wondering if there is some steel close to the firebox on the right side that is conducting the heat to that side


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## fjn (Aug 17, 2011)

brickhook said:


> I always suggest when firing a new fireplace, to build small fires to start with.
> 
> A very hot fire in a new fire place will certainly cause damage.
> 
> ...






Good point ! Cast iron stoves need to be treated the same way. The 1977 Vermont Casting Vigilant I own developed a crack last year in the fire back.Last month the new fire back I ordered came in (by the way,the original design was flawed,it was a one piece back) the replacement one is a two piece. Anyway,the instructions state "place in 350 degree oven,leave at that temp for 30 min. increase temp 50 degrees each half hr. When installed in stove,build small fires for first 7 times ! Masonry needs same approach.:thumbsup:


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## Fouthgeneration (Jan 7, 2014)

I'd saw C Js out of the thermal cracks, and caulk the cold ones with a joint filler.
Have a tin lender build an metal insert with "a funnel"to connect to metal flue liner, allow at least an 1/2" air cavity to allow air to cool the masonry.

One of the many methods use to make little rocks out of big rock at the quarries across the World include heating large rocks internally to split them...

Next attempt remember the fire box needs to be able to grow/shrink in all 3 axis X,Y,Z inside the weather box/structure every time the fire is lit.

Some time studying successful kilns, or even a couple of kitchen ovens will be well spent .

As a practical matter I don't think you'd have enough volume left for wood fires if you relaid the fire box with an air cavity and full bed fire brick.... It would be about 6-7" narrower and about 3-4" shallower...IMO


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## fjn (Aug 17, 2011)

Fouthgeneration said:


> As a practical matter I don't think you'd have enough volume left for wood fires if you relaid the fire box with an air cavity and full bed fire brick.... It would be about 6-7" narrower and about 3-4" shallower...IMO





:thumbsup::thumbsup:


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## dom-mas (Nov 26, 2011)

That firebox is 36" wide as it sits, he'd lose about +/- 3.5" if he laid up firebrick as shiners with 1/2 airspace. Plenty stable and the 1/2" airspace would do wonders in keeping it cool. ANY airspace will eliminate thermal bridging


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## NickCat11 (Nov 8, 2015)

Thanks for all the help everyone. My first plan of attack is to remove all the firebrick and some of the stone veneer on the front face. I think I can cut away at least one inch of block on either side with a chop saw and grinder. This will enable me to get a 1/2" air space and use full brick without sacrificing to much of the box. All of the cinder block cores are filled solid so I won't be jeopardizing anything structurally. It's going to be some work but I think it's doable.


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## dom-mas (Nov 26, 2011)

Personally I don't think that laying the firebrick as "stretchers" is necessary, lay them so the 2 1/4" side is down and they will be plenty stable enough, it's how the majority of firebrick are laid these days. Fireclay is more like a glue than a mortar and since the bricks are very true they stay nice and plumb so long as you lay them that way


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## fjn (Aug 17, 2011)

dom-mas said:


> That firebox is 36" wide as it sits, he'd lose about +/- 3.5" if he laid up firebrick as shiners with 1/2 airspace. Plenty stable and the 1/2" airspace would do wonders in keeping it cool. ANY airspace will eliminate thermal bridging






It is true that the vast majority of firebrick are laid as shiners,the advantage starts and stops with the initial cost reduction. Beyond that there are none,whereas,laid as stretchers,the advantages are manifold. In this case some space is saved which is important.


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## dom-mas (Nov 26, 2011)

For an outdoor fireplace built entirely out of masonry, I think 2 1/4" thick of firebrick is plenty. My opinion


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## fjn (Aug 17, 2011)

Well,let me say this,in all my years I needed to do major work on three interior fireboxes where the backs and a side were knocked loose. In every instance,I asked the ho how did this happen ? Each one said someone got a tad to aggressive throwing a big chunk of wood on to the fire.


Let me ask you this,where is the likelihood more pronounced for someone to get more aggressive throwing wood on a fire ? Is it in the living room or a backyard party in the summer when half the guests are walking around three sheets to the wind with a snoot full of suds ?


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## dom-mas (Nov 26, 2011)

I guess i don't understand why anyone is throwing wood in the fire? Don't abuse your stuff and damage wont happen. Yes drunk people break stuff, it's the price they. I don;t insist that people who are drinking only use plastic glasses either. I figure if you're adult enough to drink, you're adult enough to compose yourself, and if you can;t then it's your own fault


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## JBM (Mar 31, 2011)

Problem probaly isnt isolated to the firebox, its exacerbated with either the lintels or damper or both. Cracking the mantle like that is from something lintel on up.


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## Windycity (Oct 3, 2015)

fjn said:


> It is true that the vast majority of firebrick are laid as shiners,the advantage starts and stops with the initial cost reduction. Beyond that there are none,whereas,laid as stretchers,the advantages are manifold. In this case some space is saved which is important.


firebrick are designed to be laid as shiners per the manufacture. years ago the town i was doing a lot of fireplaces in required per code to be laid as a traditional brick or "stretcher" we talked to the brick yard about it and they contacted to manufacture and yes they are supposed to be as shiners. Yes the code has since been changed and now they no longer require it...


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## fjn (Aug 17, 2011)

Windycity said:


> firebrick are designed to be laid as shiners per the manufacture. .




???????


A brick can be laid in any position it can be laid in. In 1979,when Republic steel Corp. spent 60 million dollars building new coke ovens,there was not one firebrick laid other than a stretcher.I doubt they were intent on not following the manufactures specs. Common sense tells you the thicker the wall,the more stable and long lasting.


So many fireplaces are laid as shiners,most guys think that that is the way it automatically should be done.


Read this excerpt from this book;starting with the section titled The firebox is laid out on top of the hearth. It explains the nuances of the method. The author of the article is one of the most respected masons / instructors in his field. His two books are considered a must in masonry training programs for the past 40 years or so.


https://books.google.com/books?id=b...position are firebrick made to lay up&f=false


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## Fouthgeneration (Jan 7, 2014)

The firebrick in use appear to be "splits" ~ 4"x 8"x 1-1/8" looking back at the November thread....


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## dom-mas (Nov 26, 2011)

Fouthgeneration said:


> The firebrick in use appear to be "splits" ~ 4"x 8"x 1-1/8" looking back at the November thread....


They are. My advice is to get rid of them and re-install firebrick as shiners with at least a nominal airspace. I'm sure that JBM is correct that the flue liner is probably poured solid as well which isn;t ideal either and that the damper isn;t installed on insulation for expansion but re laying the firebox is a start


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## JBM (Mar 31, 2011)

Yeah for sure relay them on edge, with heatstop. Even without much of an airspace, 1/4, the bond break would be enough. The back wall can be sorta loosely filled with some broken pieces of the firebrick.


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