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Discussion Starter #1 (Edited)
Started A Firebox Today.

So today I started a firebox, I started to remove the old firebrick and the damper is resting on the firebrick themselves.
Behind the side walls which are plumb there is a 3" gap full of ash,soot etc.
On the back wall the firebrick start of tight to the masonry behind them and leans out leaving a 4" gap at the top, the damper was also resting on the firebrick at the back, again full of ash, soot, broken brick. The height is approx 24" from the bottom of the firebrick to the top.
The existing damper is approx 14" wide outside to outside.
The over wall depth of the opening is approx 18" ( from the front to the block that was behind the firebrick.)
What is the best way to rebuild the box without having the back lean out nearly 4" I looked for deeper dampers with no luck.
The sides are no problem as I will lay a brick on edge the butt my firebrick tight against them. ( just to close the gap)
Is keeping all the walls plumb removing the damper and installing a pop top damper on top of the flue and option.

Should have mentioned there is signs of smoke on the front of the fireplace,
 

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Discussion Starter #3
ImageUploadedByContractorTalk1423182340.525487.jpg

Photo 1 shows the front of the damper sitting 3/4" of the lintal over the opening

ImageUploadedByContractorTalk1423182423.534970.jpg ImageUploadedByContractorTalk1423182442.720169.jpg

Photos 2+3 show the back of the damper and the gap which is approx 4" wide.

Was thinking of getting a wider damper 28" building the side walls, setting the damper on the and push it tight to the back. The gap at the front I could install a lintal to close the gap.

Sorry for the crap photos.
 

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When I lay out my angles I make the top 14". Not 14" deep, but measuring the sidewall it is 14". The 4" gap at the top (if I am reading this right) is how the smoke shelf is created.

You should fill the firebox as you go, maybe put a piece of cardboard against the exterior bricks for a bond break. Keep the angle.
 

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Discussion Starter #5 (Edited)
Started A Firebox Today.

To build the firebox with such a Slope on the back wall how would I build that, would it have to be done in stages, it's not a huge job but 40 mins from the homestead, should I wait till the firebrick set before I fill?
 

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That third pic is sorta tough to see what's happening, but I don't think this is that hard....

I'm guessing you mean the damper is 3/4" off of the lintel, which, if it's the lintel over the fireplace itself, is too low......but I've seen it plenty before, and sometime they're fine.

I would not use another lintel there, just pack ceramic fiber, or some other fireproof 'insulator' there......while that wants to be closed in, the damper needs some room for expansion, and that just goes into the smoke chamber anyhow......

So it looks like the masonry backup is plumb, and the gap is caused by the brick's batter, correct? I would try to rebuild it much as it was, using the same damper if it's not damaged....

Years ago I worked for a guy that built the guts and entire chimney first, and would come in and do the fireplace last, and this may have been done that way, who knows.......it always seemed inferior to me, but I know it's not uncommon.

You don't necessarily have to do it in stages, but these are always a pain in the ass......unless you're 4'1".......:laughing:
 

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Discussion Starter #7
Started A Firebox Today.

So it looks like the masonry backup is plumb, and the gap is caused by the brick's batter, correct? I would try to rebuild it much as it was, using the same damper if it's not damaged....




My main issue is building the back wall with a 4" slope from bottom to top to meet the damper over a 24" distance. How should I support the brick?
 

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I'm not well versed on repairing/retofitting fireboxes, but have certainly done many new ones from scratch. We always build the side walls first with the appropriate angle cut on the back edge (i.e. Following the predicted slope of the back wall). Once somewhat cured, build the back wall so that it extends past, and leans against the side walls. If the span between the side walls is too great, we might stack a few blocks in the firebox to prevent the back wall from 'sagging' before it cures.
 

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So it looks like the masonry backup is plumb, and the gap is caused by the brick's batter, correct? I would try to rebuild it much as it was, using the same damper if it's not damaged....




My main issue is building the back wall with a 4" slope from bottom to top to meet the damper over a 24" distance. How should I support the brick?
I didn't see the lower part, but usually the back wall will go up plumb for anywhere from 13-16 inches........at least that's how I've done it for many years.....and I'll weave/bond those with a miter cut. You're laying them on their sides, which I don't do, but the idea is the same.

At that point, I use a compound miter cut on the sides, probably just like bytor, but for running bond I'll lay it all at once, you can go sides or back first, needing a short straight edge/level for range in between if the sides go first.......bytor's method is perhaps more common, but you don't have a lot of room to work......

Easiest thing is to cut a guide out of plywood, 2x, something fairly light......that will have your straight back, and the angle you need....this is just a guide.....I use Heatstop 50 exclusively, with full bedding, so it may be a little harder for your box......I find holding them for a few seconds helps, they will wanna creep forward a little, especially with a sharper angle.....but you'll get the feel fairly quickly......the harder the angle the tougher it is, but you can dictate that......it's the hardest part of a firebox for sure......

You can always lay the back wall plumb as well, it'll be easier, but that often makes an awfully small box.......

You also may not have room for any other masonry, I'd fill the void with perlite if it's available......
 

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As long as the angle is less than *45 (or more than *45 I can never remember but more vertical than horizontal) you just lay the brick up. The refractory acts more like a glue than mortar does. I find it best to cut the bevel into the bricks that are plumb, that way the angled brick are still pushing down more than out and the bricks against the sidewalls can help to stop them from sliding forward. If you put the bevel on the angled bricks they could possibly slide backwards before the cement has dried.
 

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In a perfect world the firebrick are laid into panels that reflect the heat into the wood pile or the room allowing fewer logs and smaller fires to burn cleanly.

Is there room to lay the back panel 4 inches wide instead of sailor fashion?


You could then saw the "corbelling" into the exposed face on the last few courses.. or saw into wedge shaped specials that keep the fireclay thickness less than an eighth of an inch the whole width of the specials bed joints,(eliminating the need for falsework) But last course will need the top cut to lay level for the damper to rest on.
One can even bow the back panel so it acts as an arch horizontally as well as vertically... leaving the intersections with the sides unbonded so the back panel can shrink and grow with out jacking the sides around.

The back panel should extend past the sides to aid in supporting the rolled panel... cut the sides as necessary to make it so.

Did the old fire place draw okay?
 

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To build the firebox with such a Slope on the back wall how would I build that, would it have to be done in stages, it's not a huge job but 40 mins from the homestead, should I wait till the firebrick set before I fill?
I have an 18" level I use to straight edge the back wall. Slap the course on, get it straight and give it a sec. It will hold. Lay them flat if you can.


Ive also use a piece of strapping before I had the little level.

Normally I would do the sides then the back, but seeing as there is a fireplace in the way already , you might find it easier to do it more or less as you go, so that it can be filled right. You woulnt want to fill the whole thing after your done. (without practice first)
 

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I have an 18" level I use to straight edge the back wall. Slap the course on, get it straight and give it a sec. It will hold. Lay them flat if you can.



:thumbsup::thumbsup:


As JBM suggested,lay them as stretchers with joints as thin as a playing card......they will stay put.


You will probably have to cut a spit at top to compensate for tight joints.


If they were laid that tight as stretchers originally,you would not have the job now.:laughing:
 

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Discussion Starter #14
I have an 18" level I use to straight edge the back wall. Slap the course on, get it straight and give it a sec. It will hold. Lay them flat if you can.







:thumbsup::thumbsup:





As JBM suggested,lay them as stretchers with joints as thin as a playing card......they will stay put.





You will probably have to cut a spit at top to compensate for tight joints.





If they were laid that tight as stretchers originally,you would not have the job now.:laughing:

Can't lay them flat, the fire place is existing, I think I will build the side walls then the back maybe have a few 2x2 ( or whatever is at the yard) and as it begins to lean out just put a brace to hold each row.
 
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