# No steel throat



## JBM (Mar 31, 2011)

Wanted to share how we build a throat without irons.


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## superseal (Feb 4, 2009)

Nice...what's the flue to the left? can't quite make out the size of it...


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## JBM (Mar 31, 2011)

Just an 8x8 for the woodstove in the cellar. Its going to get wrapped with 4" stone, dont know what kind yet.


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## CJKarl (Nov 21, 2006)

Do you support the damper with angle? I think I would have to fight the inspector to get that passed.


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## JBM (Mar 31, 2011)

No the damper sits on the firebrick, then the throat is sealed off the damper. The underside of it is tapered from 4" to 8" as well.


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## CJKarl (Nov 21, 2006)

We must use angle iron to support the front edge of the damper. Using the damper itself to support the masonry is a big no no around here.


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## JBM (Mar 31, 2011)

Wait , what? You put an angle iron under the damper flange on the front of the firebox?

Well either way, you would just build a few rows of brick under the arch and it would still have less steel in it.

If you used a lemance damper, you would need an iron across the firebox, so I might just go that route on every chimney if I were in that situation.


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## JBM (Mar 31, 2011)

After thinking about it, im sure the intent of the code was for the guys who support the throat on the damper/ firebox. If you can build a self supporting throat im sure the inspector would not require more steel put inside the firebox area.


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## brick (May 8, 2012)

Yup, can't use the damper for anything structural. It should be independant with the firebox for rebuild, expansion, contraction so forthe. Agree with JBM in his thinking on steel, less is more.


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## Tscarborough (Feb 25, 2006)

They built "modern" fireplaces long before angle iron (or dampers) were common, both are optional.


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## dbrons (Apr 12, 2010)

What I do lots of times with an arch is build a lintel just above the damper with bond beams and two lengths of #4 rebar which extend and hook into grout cells in the side walls. 

Of course I reinforce a shallow arch like JBM has there as well by building it with little 6" X 4" U blocks I make up with 6" long pieces of 4" hollow block ripped in half. throw a piece of #3 in there and some concrete mix  I can't help it - they reinforce everything out here.

Dave


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## smeagol (May 13, 2008)

You may need wider piers/abutments to deal with lateral forces created by the low segmental arch.


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## dom-mas (Nov 26, 2011)

I don't get it. I don't think JBM is supporting anything with the damper. The throat is already in, just waiting for the firebox which will have the damper on top of it, the damper gets sealed to the throat so there's no smoke leaking. Why would it need an angle?


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## JBM (Mar 31, 2011)

dom-mas said:


> I don't get it. I don't think JBM is supporting anything with the damper. The throat is already in, just waiting for the firebox which will have the damper on top of it, the damper gets sealed to the throat so there's no smoke leaking. Why would it need an angle?


I grew up building the throats just like in the picture but with 2 - 2x3 angle irons, straight across. This allow us to save the fireplace for a rain day.

The alternate way of doing them is to build the fireplace once the chimney is up "enough". The throat was then built off the damper. The purpose for the angle iron as mentioned by Carl, is for this situation where some of the masons built the fireplace before the throat.

If you remember back to a photo where the firebox was filled very wacky with blocks on edge and nothing against the brick to support the throat. This is sometimes a result of a sloppy mason who builds the fireplaces first. They support the throat off the damper therefore dont pay any attention to the 4" lining inside of the chimney, that is supposed to support the throat, they fill the firebox poorly with no structural integrity and cracking/movement will result. 

In the way I build the throats, I can stand blocks on edge as fill if I want to , as the fill isnt responsible for supporting anything. I also have 8" of masonry built to the first flue, not the 4" like was in the picture a few months ago.


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## dom-mas (Nov 26, 2011)

yeah i don't know. in my experience the throat is supported by the backup material, ie the structural 6" or 8" semi solid block and the firebox is independent of it with the damper sitting on top


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## 2low4nh (Dec 12, 2010)

I always build my box first. the back wall goes up usually at the same time. solid fill around the box, I don't get how you guys are building your box,damper and fill when the throat is already in place. my damper sits on top of the box usually angle across the front insulation to stop bridging from throat to damper. guess I would have to see the whole build process I just dont get how everything goes together easily enough to do it this way.


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## dom-mas (Nov 26, 2011)

I've never done the throat before the box either but I don't see what is wrong with doing it since the structure is already in, there's nothing for the damper to support

I do see the advantage of getting block up so the building can be dried in and the box and facing can be saved for rain days, I think I started a thread about it earlier this fall, but I can't get my head around how it would actually be done.

JBM, next time you do one like this, could you get some pics of the firebox and damper install?


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## bytor (Jan 23, 2010)

I too am curious about this method. We have always built our fireboxes/throat/smokechamber first, but I can see that there would be advantages to your method JBM. 

We have a rough-in to start later this week and have to get it up in a hurry as it carries the ridge beam for the roof... Given that temperatures are in the -20o range, I don't look forward to having to deal with all the tarping and heating for the brick saw etc. etc.... This would seem to be the perfect opportunity to follow your lead, and simply worry about the column of block for now. 

So... Questions; 

Do you have any pics looking up inside your rough-in? 

I assume the flues are already in place... Where, in relation to the arch is the bottom of the lowest flue?

How are the flues supported?

At what height will the damper be in relation to the existing opening?

It would seem to me, that as long as the arched opening is high enough, then building the firebox with appropriate back-up, installing damper and smoke chamber would be reasonably straight forward.. Might be tricky making the transition from smoke chamber to flue...

Thanks.


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## JBM (Mar 31, 2011)

dom-mas said:


> I've never done the throat before the box either but I don't see what is wrong with doing it since the structure is already in, there's nothing for the damper to support
> 
> I do see the advantage of getting block up so the building can be dried in and the box and facing can be saved for rain days, I think I started a thread about it earlier this fall, but I can't get my head around how it would actually be done.
> 
> JBM, next time you do one like this, could you get some pics of the firebox and damper install?


Sure.


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## JBM (Mar 31, 2011)

bytor said:


> I too am curious about this method. We have always built our fireboxes/throat/smokechamber first, but I can see that there would be advantages to your method JBM.
> 
> We have a rough-in to start later this week and have to get it up in a hurry as it carries the ridge beam for the roof... Given that temperatures are in the -20o range, I don't look forward to having to deal with all the tarping and heating for the brick saw etc. etc.... This would seem to be the perfect opportunity to follow your lead, and simply worry about the column of block for now.
> 
> ...


Lets assume the opening is done with 2x3 irons instead of the arch, it is pretty similar to the way you do it over the front of the firebox. The angled firebrick you cut in one of your posts is on the second course over the iron. 

I corbel out with irons to 8" then run 4" up for the chimney, the inside 4" wall carries the flue and is tapered to the inside flue dimensions. 

On inside chimneys we need 8" to the first flue, outside chimneys is 6".

So on inside chimneys we run a 4" wall up inside which carries the flue and tapers to the same triangle as the other wall. 

Split an 8x18 flue for the slabs that sit on the angle created. Lay brick ontop of it till the flue, wrap the flue, the rest is the same. 



















On a 5' chimney I would use 4' irons and an 18" flat stock to bridge where the furnace flue is. 

To make the arch, just make one with a 45 degree angle on some wood until you have an 8" chunk of wood.


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## JBM (Mar 31, 2011)

bytor said:


> At what height will the damper be in relation to the existing opening?
> 
> It would seem to me, that as long as the arched opening is high enough, then building the firebox with appropriate back-up, installing damper and smoke chamber would be reasonably straight forward.. Might be tricky making the transition from smoke chamber to flue...


You want to make sure you put the arch or the irons up high enough to fit the damper in. 8-10 inches. 

The smoke chamber is built to carry the fireplace flue. Only thing that needs to be installed is the damper, if using a vestal poker, some insulation on top of it, put up a wall to up under the throat.


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## dom-mas (Nov 26, 2011)

So to get this straight (and i think I have) You've built the foundation/ash dump, backup, throat, smoke chamber chimney and have installed the flue liners. Correct? 

You have yet to build the box and install the damper and fill in the area between the damper and arch. Correct?

And obviously face

Sao long as the smoke chamber is built I can see how this would work. I just couldn't imagine building a smoke chamber with the backup already built


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## dom-mas (Nov 26, 2011)

dom-mas said:


> fill in the area between the damper and arch.


Is this the part that has CJKarl asking about having material on top of the damper?


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## JBM (Mar 31, 2011)

dom-mas said:


> Som to get this straight (and i think I have) You've built the foundation/ash dump, backup, throat, smoke chamber chimney and have installed the flue liners. Correct?
> 
> You have yet to build the box and install the damper and fill in the area between the damper and arch. Correct?
> 
> And obviously face


Right. On an exterior chimney code requires 6" on the back wall to the first flue. Transition from laying a 4" block to a clay brick on edge. Build the smoke chamber, pretty much exactly the way the Rumford kit looks like, build it with the 4" wall over the irons and the brick on edge on the back wall. Should have a tall throat to the first flue. 

On an interior chimney code requires a full 8" wall to the first flue. Transistion from the 4" block to clay brick. Lay up the back wall, draw out the smoke chamber and slam in bricks to the pencil mark. Cap with slab of 8x18. 

Quick and easy.


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## JBM (Mar 31, 2011)

dom-mas said:


> Sao long as the smoke chamber is built I can see how this would work. I just couldn't imagine building a smoke chamber with the backup already built


What do you mean by backup?


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## JBM (Mar 31, 2011)

dom-mas said:


> Is this the part that has CJKarl asking about having material on top of the damper?


No, you need a wall to seal it off and get the 8".


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## JBM (Mar 31, 2011)

Should note that all this is parged inside. depending on how I feel I might even hit it with a sponge ...shrug...


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## dom-mas (Nov 26, 2011)

The backup material that the facing stone will tie to. It isn't really necessary for the fireplace since the chimney is 6" or whatever back from the firebox face but since they want the face to go up straight rather than stepping back you have backup material for the face stone


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## JBM (Mar 31, 2011)

No the stone is essentially a veneer. You build a real chimney with the block. Full 8" codes are met ect. dont rely on stone to meet your codes.


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## dom-mas (Nov 26, 2011)

JBM said:


> No, you need a wall to seal it off and get the 8".


What wall? 

Your damper is installed below the arch correct? So there is space between damper and the intrados of the arch. You need to seal that area with at least 4" if you have 4" of veneer or 8" if you have no veneer


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## JBM (Mar 31, 2011)

dom-mas said:


> What wall?
> 
> Your damper is installed below the arch correct? So there is space between damper and the intrados of the arch. You need to seal that area with at least 4" if you have 4" of veneer or 8" if you have no veneer


Right, were saying the same thing, :laughing:


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## dom-mas (Nov 26, 2011)

Right, and I think that is what Karl was wondering about. The small amount of volume being carried by the damper

And I agree. While you CAN include the veneer as part of the fireplace it is better not to use it as part of the 6 or 8" since you never know if someone will tear it off later to drywall it or put up some tile or thinstone of some sort.


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## 2low4nh (Dec 12, 2010)

so really you are saving maybe 6 hours labor doing it this way. I understand the way you built it I dont care for the seal around the damper. I usually have to fight for room due to space to get the damper in. I could just see trying to build the box and holding a damper up fumbling around and trying to squeeze inside the box all a big pain in the ass.


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## JBM (Mar 31, 2011)

Probably 6 hours, i dunno. I can slam in a throat in an hour. It takes me till 2ish to do the fireplace and clean up. I dont think I could be at the same place on a chimney with the same 7 or so hours doing it the other way.

Plus some of the time im doing the face on a rain day.


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## 2low4nh (Dec 12, 2010)

for me usually box back wall and fill with damper in place ash dump cut in cold air etc usually the first day throat and all block work for first floor done on day two with a few feet of tile depending on lay out size etc.


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## bytor (Jan 23, 2010)

I'm not so sure that this exact method would work for us after all...

We ALWAYS build our throat/smoke chambers out of 2-1/2" firebrick and refractory mortar....and would rather have this material bearing on the properly bonded 'fill' around the firebox rather than having to try to tie it in to the chimney structure for 'temporary' support. I understand that proper support can be achieved with proper corbelling etc... just not my preference.

What I would like to explore though, is raising the height at which you have your arch (or lintels) JBM, to something like 7 or 8 feet, leaving enough space so that ALL of the guts of the fireplace can be built later. So essentially we would have the block column with flues. The Smoke chamber would then be built up under the flues to provide the permanent support.

It's the temporary support of the flues that has me stumped.

I have seen some rough-ins done like this with the bottom flue encased in a 'collar' of concrete to lock it in place, not a great idea in my opinion... although I wonder about casting something out of refractory that the flue could sit on top of rather than pass through...

Hmmmm....

P.S. we also use custom made flat dampers as opposed to the Vestal brand, and would need a little more 'access' for the installation...


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## denver 2 (Jan 1, 2009)

Bytor,


We build our throats with block first and add our firebox later by taking the block up approx. 16 inches higher than the firebox and then crossing the opening with a masonry lintel stood up on edge and then a row of six in deep solid slabs on top of that and then another masonry lintel laid flat. This gives you a inside ledge of 4 inches to build what we call a jug. We dry lay four to five courses of 4 inch solid block on the inside edge of the lintel and then scribe a line from the box opening below to the desired flue size above. We then cut block and lay and repeat same process on back wall. Then we cut 4 foot masonry lintels into 2 foot lengths and lay up the sides of the throat. After building the throat we lay 4 inch block up the face of the lintel for the veneer to be attached or whatever. The flue can be set right after the jug is complete. This method is extremely fast and offers a smooth slope and is much stronger than corbeling in my opinion. When we install the firebox later we have plenty of room to install the damper and then fill the gap between the damper and lintel with firebrick. Next time I do one I will take pictures.


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## dom-mas (Nov 26, 2011)

Really, form and pour the hearth, run fresh air intake, layout and build inner hearth in a shiner position, and build firebox in a stretcher position in less than a day. You're pretty fast


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## JBM (Mar 31, 2011)

Bytor I get what your saying. Ive forensically looked at how you build your throats, and it is better for sure. The throats I build are supported off the interior walls of the chimney, just like you use the fill , i use the walls. Semantics I suppose. With a flue in the cellar something has to be bridged across to start the throat, but when filling the firebox that side is built to support the wall that tucks up under this. Again this is supported.

The corbelling to 8" off the iron or arch, one way or the other it has to be corbeled out whether its off the front of the firebricks or off the angle iron, either way the irons span into the masonry chimney. I always build 8" cheeks on the sides of the chimney, if I were to use an iron it bears on the inside 4" here.

From looking back at your throats I forgot how you taper in at the top of the firebox, that was one of the details I liked, it replicated the rumford throatr. Im not sure how you would implement this with my design. It might be tough as once im at the top of the firebox, im done and setting the vestal damper. 

As far as building the entire smoke chamber with firebrick, I just came from your site and the smoke chamber you build is what it looks like on mine, prettier for sure, I top the corbel with a slab off an 8x18 and parge the inside. 

Except for the issue at the top of the firebox and how you would make your damper work, I could make our throat meet your criteria for build quality.


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## JBM (Mar 31, 2011)

dom-mas said:


> Really, form and pour the hearth, run fresh air intake, layout and build inner hearth in a shiner position, and build firebox in a stretcher position in less than a day. You're pretty fast


I dont know if he meant all that, I cant tell.

I did labor for a crew that would throw up the base, sprinkle mortar or portland powder on the hearth and start on the firebox. 2 guys would be up to the roofline on the first day and the guy who did the cellar/poured the hearth/started the fireplace would finish the fireplace the next day and the 2 on the staging would finish the chimney by 3.

2 Day chimneys week after week with steps being built as the truck was loaded. 75 chimneys a year no problem. All with angle irons supporting the throats.

Of coarse this was with 8 pitches, 8x12s, 20" chimneys, no partition walls.


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## dom-mas (Nov 26, 2011)

2low4nh said:


> so really you are saving maybe 6 hours labor doing it this way.


I don't know, sounds like that's what he's saying. Of course a crew of 5-10 guys can do a lot more in 6 hrs than one installer and a labourer.


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## dom-mas (Nov 26, 2011)

Any way, I don't think that the method you use would be the way i would do a FP but I do see the advantage of drying the house in and saving indoor work for a rainy day. Even if it is only 6 hrs most guys would rather have 6 hrs of work on a rain day than negative 6hrs on their pay cheque


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## JBM (Mar 31, 2011)

Its just faster, it isnt better necessarily. Better comes with the mason. 

On an outside chimney with 2 masons a guy gets the cellar up by 930 and works on forming the hearth. The guy on the outside is up at the beginning of the throat by 11. Both of them work the rest of the day outside and are halfway up the house at 4 when one goes down to help the laborer pour the hearth. 

If we had to wait to build the firebox to do the throat, what would our day look like? Guy in the cellar and other guy gets the brick up 5' or so then pour the hearth and go home(thats all could be done). Next day both guys go in and build the firebox and throat. Then go outside and get the chimney cut over and a few feet up? It might be impossible to finish on the next day, unless at least 7 or 8 feet of the stack was built, which is unlikely. So now were into the 4 th or 5th day to finish a chimney?

Going home early that day costs too much. It prevents any chance at a 2 chimney week. Its not the 6 hours, Its being forced not to work because the hearth is not poured.

An inside chimney is different because you have to pour the hearth before any more work is done. Doing the firebox before or after really has little effect on an interior chimney aside from cold weather or rain.


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## dom-mas (Nov 26, 2011)

Whoa, a guy getting the foundation done in 2.5 hrs. Most that I see are 10-15 blocks per course with 4 outside corners, 12 courses is 120-180 blocks in 2.5 hrs?


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## Diamond D. (Nov 12, 2009)

Never been a fan of using block and lintels in the smoke chamber or the throat, although I know a lot of guys that do it.
It may be easier and faster, but IMHO, it can't take the heat for the long haul.

Maybe it's just how I was taught and I have a hard time with change, but I'll continue building the hearth, box, shelf, chamber and on up for now.
If its a rush, I'll get another man or two for a couple of days to get through the roof.

Having the stonework for a rainy day is good enough for me.
I can always find things to do when it rains, including putting up a tarp.

D.


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## dom-mas (Nov 26, 2011)

I don't think JBM uses directly in the throat or smoke chamber. I believe he uses clay brick parged with HTC


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## JBM (Mar 31, 2011)

dom-mas said:


> Whoa, a guy getting the foundation done in 2.5 hrs. Most that I see are 10-15 blocks per course with 4 outside corners, 12 courses is 120-180 blocks in 2.5 hrs?


No the chimney jog is a poured foundation. The guy in the cellar is only laying the 2 1/2 blocks for 11 courses.


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## JBM (Mar 31, 2011)

Ya transition from the block to the backer bricks.


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## JBM (Mar 31, 2011)

JBM said:


> No the chimney jog is a poured foundation. The guy in the cellar is only laying the 2 1/2 blocks for 11 courses.


In regards to an outside chimney, on a house.


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## dom-mas (Nov 26, 2011)

JBM said:


> No the chimney jog is a poured foundation. The guy in the cellar is only laying the 2 1/2 blocks for 11 courses.


OH, I've only seen totally separate footings where the entire foundation for the FP is done in block. the FP is such a different weight/density from the rest of the house that it settles differently from the wood framed building


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## dbrons (Apr 12, 2010)

Interesting techniques JBM. I build mostly outdoor fireplaces, or on a concrete slab, so I don't usually have to wait for a hearth to harden. 

But even though I can see you might save a few bucks with that style, I wouldn't go that way mainly because I wouldn't want to build a firebox all hunched over or on my knees. 

Dave


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## 2low4nh (Dec 12, 2010)

your always hunched over on a box they are never up waist high, exterior/interior chimnies are nice when the foundation is your back 3 walls. most of ours are all center fireplaces. the base and pad usually done the first day. I have only been able to get the box on a hanful of times.


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## dbrons (Apr 12, 2010)

not so on the boxes I usually build 2low4nh. And whatever the height, I'd prefer not having a shallow brick arch to bonk my forehead on. 
Dave


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## JBM (Mar 31, 2011)

dbrons said:


> Interesting techniques JBM. I build mostly outdoor fireplaces, or on a concrete slab, so I don't usually have to wait for a hearth to harden.
> 
> But even though I can see you might save a few bucks with that style, I wouldn't go that way mainly because I wouldn't want to build a firebox all hunched over or on my knees.
> 
> Dave


This technique really is best for a single facing for the fireplace, or even 3 sides I suppose. An outdoor chimney/fireplace wouldnt benefit from skipping the firebox like I do. 

I dont ever bump my head either :no:


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## JBM (Mar 31, 2011)

How about an update. Yesterday we had yet another snowstorm, guess where I was 

Here


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## dom-mas (Nov 26, 2011)

looks great. Laid the firebox up with stretchers?


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## JBM (Mar 31, 2011)

Yeah, always do with stone. Just looks better.


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## dom-mas (Nov 26, 2011)

interesting


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## JBM (Mar 31, 2011)

On this fireplace the owner wanted it to look "lumpy" and rustic. Its more lumpy in person I think. In an effort to keep it "lumpy" there are no plumb lines. Its easy to obsess over the corners when there is a line there to constantly remind you that you should have knocked off that little tidbit or whatever. It is also nerve racking constantly thinking about the corners if they moved or not. a 4" mantle is going on tomorrow and a 3" hearth. Just granite, couldnt get a matching stone.


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## dom-mas (Nov 26, 2011)

lumpy, now there's a descriptive word that's hard to nail down


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## Diamond D. (Nov 12, 2009)

Hmmm, Lumpy?
Hey Wally, It still looks pretty sharp and flat... Doesn't it Beve'? :jester:

Lookin' good,
D.


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## JBM (Mar 31, 2011)

Couldnt finish it today


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## brickhook (May 8, 2012)

Nice looking work....it's going to look awesome when you get finished!


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## fjn (Aug 17, 2011)

Looks great ! love the extremely uniform joint sizing. A mark of a true craftsman.


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