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Offline SC

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WFO Construction - stuck on two things
« on: July 11, 2014, 05:44:38 AM »
I am into the construction of my WFO. See picture. I am stuck on two design items.

I am building it from a scavanged insert and there is no "tunnel" per se with an opening upon which to place a chimney. It is a neopolitan style oven so the smoke will roll out of the oven opening. I bought a rectangular 8 inch by 12 inch terra cotta flue liner, 24 inches high and need to position this above the opening. I am struggling trying to figure out how to design this so could use help! Should I just forget about a chimney or am I going to have to somehow brick a chimney around the face of the oven? If I use brick I imagine I will need a piece of angle iron above the oven opening - will this get screaming hot and represent a hazard to my forehead everytime I slide a pizza into the oven?

Second question - once I have the chimney (or no chimney) done, I am ready to wrap the thing in ceramic blanket, and hold that in place with chicken wire. I want an igloo design (ie I do not want to build a frame structure). I have access to lots of granite quarries.  I want the igloo covered with smallish 1-2 inch thick flagstone pieces, or perhaps granite rocks - both set in mortar. The masonry shops I have spoken with have recommended that I simply slap a 1/2 inch layer of regular cement right on top of the chicken wire/insulation.
Will this work or is the underlying layer of insulation going to be too spongy to provide enough support? Is regular cement OK or do I need something with more adhesive (thin-set has been mentioned).

Last question. I put refractory mortar over the oven seams as you can see in picture. Did I use enough?

P.S. Sorry about picture orientation - cannot seem to figure out how to change it

Thankyou!
« Last Edit: July 11, 2014, 05:52:12 AM by SC »

Offline Tscarborough

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Re: WFO Construction - stuck on two things
« Reply #1 on: July 11, 2014, 09:11:57 AM »
You have the lintel laying right there.  Brick the sides, mount the precast lintel and put the flue on top.  You will need to do something to secure the flue, so consider bricking the whole chimney.

Offline stonecutter

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Re: WFO Construction - stuck on two things
« Reply #2 on: July 11, 2014, 09:46:52 AM »
Cool base, I knew you where in PA by that stratified stone before I glanced at your location.  If you posted using an iPhone or iPad,  you need to edit the rotation before uploading it on the forum.....ask me how. I know.....
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Offline stonecutter

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Re: WFO Construction - stuck on two things
« Reply #3 on: July 11, 2014, 10:26:11 AM »
I am into the construction of my WFO. See picture. I am stuck on two design items.

I am building it from a scavanged insert and there is no "tunnel" per se with an opening upon which to place a chimney. It is a neopolitan style oven so the smoke will roll out of the oven opening. I bought a rectangular 8 inch by 12 inch terra cotta flue liner, 24 inches high and need to position this above the opening. I am struggling trying to figure out how to design this so could use help! Should I just forget about a chimney or am I going to have to somehow brick a chimney around the face of the oven? If I use brick I imagine I will need a piece of angle iron above the oven opening - will this get screaming hot and represent a hazard to my forehead everytime I slide a pizza into the oven?

Second question - once I have the chimney (or no chimney) done, I am ready to wrap the thing in ceramic blanket, and hold that in place with chicken wire. I want an igloo design (ie I do not want to build a frame structure). I have access to lots of granite quarries.  I want the igloo covered with smallish 1-2 inch thick flagstone pieces, or perhaps granite rocks - both set in mortar. The masonry shops I have spoken with have recommended that I simply slap a 1/2 inch layer of regular cement right on top of the chicken wire/insulation.
Will this work or is the underlying layer of insulation going to be too spongy to provide enough support? Is regular cement OK or do I need something with more adhesive (thin-set has been mentioned).

Last question. I put refractory mortar over the oven seams as you can see in picture. Did I use enough?

P.S. Sorry about picture orientation - cannot seem to figure out how to change it

Thankyou!

1) if you trim back your insulation, you'll have room to build a vent arch with a throat opening in which to set your flue.

2) You have some things to consider here.  First, what is your insulation thickness?  Second, don't 'slap' stone onto the insulation because it will compress it down, and the bond will fail from tensile stress....chicken wire won't do squat to stop it. A better method would be to put a 3"-4" layer of vermiculite or perlite 'crete over the ceramic blanket.  After it dries then you can mortar to it.  And if you want reinforcement in the bed mortar use wire lath not chicken wire.

If you are bedding the stone as a veneer ( flat side facing out ) then you will need to strengthen the bond between the stone and mortar.  Use a slurry of acrylic additive/Portland  or type S and paint the backs of the stone before bedding it.   And when the mortar cures, get yourself a good quality sealer (silpro is would be great for this one) to help with moisture intrusion.  In the  winter, assuming there is no shelter over the oven, put a tarp over it.....but don't lay the tarp in contact with the shell.  Be sure to use something to allow air flow underneath the tarp, to keep condensation from seeping into the veneer.

Even with the extra help, bedding thin stone as a veneer is weak and it's success relies 100% on bond.  Don't just slap the stone on the oven.   Most of those guys have zero construction experience...they are salesmen.
« Last Edit: July 11, 2014, 10:28:18 AM by stonecutter »
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Offline SC

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Re: WFO Construction - stuck on two things
« Reply #4 on: July 11, 2014, 11:24:33 AM »
Yikes.  The stone sounds like more than I bargained for as well as being high maintenance (winter care - this is Northern Ontario where winters are harsh). I just checked out the cost of the veneer and it is about $5 per square foot, so assuming I need 100 sq ft - thats another $500 on top of what I have spent already.  Maybe I will have to cave in and just stucco it.... I assume stucco would be much less expensive, less work and less maintenance than stone?

By the way, I thought the piece laying on the ground there in front of the oven was the (lintel?) piece to go on top of the opening to create a place for the chimney/flue as well.  But after I got the oven together I realized it was actually the landing piece.  There are lugs on it that slide under the front of the oven, and the original oven floor had a tongue (landing) that would have fit perfectly into that piece. Mystery solved. It never sat correctly on the top it was unbalanced and the lugs did not go anywhere sensible. So, I am not going to use that piece. So, I am left with trying to McGyver a chimney.  There remains the suggestion that no chimney is actually needed because the lenght is not likely to cause much of a draft anyway. I know the merits of chimneys have been debated on this site but I wasn't able to draw any conclusions about whether I need one.

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Offline SC

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Re: WFO Construction - stuck on two things
« Reply #5 on: July 11, 2014, 11:33:51 AM »
Stonecutter thanks for the tips.  After looking at the stone, if i do go with it, I am going to use 2 inch to three inch thick pieces. The one inch looked too uniform and I am going for more of a rustic look to match the base.
I did pick up some stucco lath, which I was going to put over the chicken wire to provide more support for the stone.  Where i am located it is very difficult to get decent supplies.  Even picking up additional refractory cement ((I brought stuff from Philly but ran out) was over an hour trip and costs $30 bucks for 10 pounds. So, my point is, the perlite solution you have suggested is problematic. With the use of stucco lathe, what if I use regular cement and put a half inch layer or so, let it dry, the mortar and apply the stone. I assume a half inch of concrete won't crush the blanket, as long as I use the lathe, and when dry will support the stones? Please tell me if i am wrong. The other additives you suggest for painting the back of the stone. Are they readily available at a big box store, or would i need a specialty masonry store (which is a problem here).

Offline SC

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Re: WFO Construction - stuck on two things
« Reply #6 on: July 11, 2014, 11:35:24 AM »
Sorry, one last thing Stonecutter. Can you explain, or point me to a place to see what you are describing for the flue and chimney?

Offline SC

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Re: WFO Construction - stuck on two things
« Reply #7 on: July 11, 2014, 11:36:54 AM »
I have not applied the insulation yet. I bought 3 rolls with the idea that it would give me 2 inches of cover - but I will see what I actually get later today.

Offline stonecutter

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Re: WFO Construction - stuck on two things
« Reply #8 on: July 11, 2014, 11:51:59 AM »
I'm tied up until later, I'll be happy to answer your questions tonight!
When we build, let us think that we build forever.
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Offline SC

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Re: WFO Construction - stuck on two things
« Reply #9 on: July 11, 2014, 03:11:24 PM »
Excellent. Got insulation on lath on.  Good 4 inches of insulation. Went to quarry. The selection here is beautiful so I am all in on the granite. Plus, I figure, I can get by with 50 sq ft rather than 100.  So, i need to mix up the potion you suggested to attach the rock. I am now wondering whether it is necessary to put down a layer of cement and let it dry - at least on the sides which are vertical. Once i have the sides done, I could do the top with a layer of concrete (say 1/2"?), let it dry, then lay the stone on top? Do i need the perlite concoction given I have 4" of ceramic blanket?

I'd like to put a granite lentil in as well, to hold up the chimney/flue. How much heat will this be subject to because I know granite doesn't do so well in high heat? The lentil will only be about 4" from the oven door. Maybe if i craft a metal support under the lentil so that even if the granite cracks the whole chimney won't come down?

Finally, can I attach granite flagstone to the terra cotta flue? What is the best way to do so?

Sorry for peppering you with questions but like most people on this board I am probably a bit OCD. Started on this damn thing at 4 am and need to get it done so I can move on....
« Last Edit: July 11, 2014, 06:31:34 PM by SC »

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Offline stonecutter

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Re: WFO Construction - stuck on two things
« Reply #10 on: July 11, 2014, 06:24:24 PM »
Yikes.  The stone sounds like more than I bargained for as well as being high maintenance (winter care - this is Northern Ontario where winters are harsh). I just checked out the cost of the veneer and it is about $5 per square foot, so assuming I need 100 sq ft - thats another $500 on top of what I have spent already.  Maybe I will have to cave in and just stucco it.... I assume stucco would be much less expensive, less work and less maintenance than stone?

By the way, I thought the piece laying on the ground there in front of the oven was the (lintel?) piece to go on top of the opening to create a place for the chimney/flue as well.  But after I got the oven together I realized it was actually the landing piece.  There are lugs on it that slide under the front of the oven, and the original oven floor had a tongue (landing) that would have fit perfectly into that piece. Mystery solved. It never sat correctly on the top it was unbalanced and the lugs did not go anywhere sensible. So, I am not going to use that piece. So, I am left with trying to McGyver a chimney.  There remains the suggestion that no chimney is actually needed because the lenght is not likely to cause much of a draft anyway. I know the merits of chimneys have been debated on this site but I wasn't able to draw any conclusions about whether I need one.

Northern Ontario?   Your location says Philadelphia, so I assumed PA.....that and the stone is the exact type PA is known for.  I know it runs from PA through Upstate NY but wasn't sure about Canada, but I digress.....


As for a chimney, being outside....you don't NEED one, but it's nice to exhaust the gases and oven heat above and away from the oven finishes.  That and if you have a windy day or if the oven faces prevailing wind, a properly sized vent, throat and flue will keep the exhaust out of your face. 

About your oven finishes,  nothing is maintenance free.   And a harsh winter can be harder on stucco than a veneer, and it's more difficult to repair and blend in stucco than stone cladding.    Maybe a tile mosaic would be better...there's even a couple on this site you can check out.  I still think you should use sealer on the grout, even if the tile you use is water impervious like porcelain or glass.
« Last Edit: July 11, 2014, 06:28:22 PM by stonecutter »
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Offline stonecutter

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Re: WFO Construction - stuck on two things
« Reply #11 on: July 11, 2014, 06:34:41 PM »
Here you go...
When we build, let us think that we build forever.
John Ruskin

Offline TXCraig1

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Re: WFO Construction - stuck on two things
« Reply #12 on: July 11, 2014, 06:49:25 PM »
Glad to see you are getting the oven put together.
"We make great pizza, with sourdough when we can, baker's yeast when we must, but always great pizza."  
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Offline stonecutter

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Re: WFO Construction - stuck on two things
« Reply #13 on: July 11, 2014, 06:53:53 PM »
Excellent. Got insulation on lath on.  Good 4 inches of insulation. Went to quarry. The selection here is beautiful so I am all in on the granite. Plus, I figure, I can get by with 50 sq ft rather than 100.  So, i need to mix up the potion you suggested to attach the rock. I am now wondering whether it is necessary to put down a layer of cement and let it dry - at least on the sides which are vertical. Once i have the sides done, I could do the top with a layer of concrete (say 1/2"?), let it dry, then lay the stone on top? Do i need the perlite concoction given I have 4" of ceramic blanket?
  with the thickness of your stone (1"-2") you are going to be  between 15-25 lbs per squ ft...so you are going to get compression.  To what point, I can't say....what I will say, is that I think it's going to cause you problems.   It would be like dry setting a stone walkway and mortaring the joints.  Your substrate ( the oven insulation) is too flexible for a rigid system( stone veneer).  Of course because it's insulation, you aren't getting away from compression no matter what you do. So if it was me, I would want a layer of perlcrete at 5:1 and 2" thick before the stone veneer goes on.    And more insulation is never a bad thing, unless you have no room left on your slab for finishes.
I'd like to put a granite lentil in as well, to hold up the chimney/flue. How much heat will this be subject to because I know granite doesn't do so well in high heat? The lentil will only be about 4" from the oven door. Maybe if i craft a metal support under the lentil so that even if the granite cracks the whole chimney won't come down?
Yes, if you want a granite lintel, then use angle iron.  Granite should be isolated from too much thermal cycling, though...the quartz content makes it susceptible to cracking...and it will if there isn't enough mass to distribute the heat. 
Finally, can I attach granite flagstone to the terra cotta flue? What is the best way to do so?
No, never put any kind of masonry in direct contact with the flue liner.   It needs room to expand.  If you are new to masonry or don't feel confident to leave a cavity between the flue and the stonework, you can wrap the flue with ceramic blanket or fill the cavity with loose insulation as you build your courses up
Sorry for peppering you with questions but like most people on this board I am probably a bit OCD. Started on this damn thing at 4 am and need to get it done so I can move on....

Better to ask questions now, than build a clunker you have to demolish later!

Also, to a question you asked earlier....
 Don't bother with more mortar parging over the oven seams..it's just going to crack anyway.  If you are really OCD about it, then put a layer of mortar over the joint, then a strip of lath 4" wide, then more mortar.  It won't stop the joint from cracking, but when it opens up, then joint stays covered.
« Last Edit: July 11, 2014, 06:56:46 PM by stonecutter »
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Offline SC

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Re: WFO Construction - stuck on two things
« Reply #14 on: July 11, 2014, 11:51:55 PM »
Thanks man. Your advice is really great!

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Offline SC

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Re: WFO Construction - stuck on two things
« Reply #15 on: July 11, 2014, 11:55:14 PM »
And slab room is getting tight but only on the back - where if I over-run the slab it won' t be a problem, at least cosmetically.

Offline SC

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Re: WFO Construction - stuck on two things
« Reply #16 on: July 12, 2014, 08:06:30 AM »
Can anyone advise on how to build the chimney? You have said the (8x12) terra cotta flue needs insulation filled space between it and the stone walls of tge chimney. What do I do and in what order?
1. Fasten an angle iron across the top of the pre-fab brick vertical columns which are on either side of door?
2. Seat the 12 inch edge of the flu on the iron and the other 12 inch edge on rhe top of oven?
3. Doing this will mean that 4 inches of the flue will be sitting on the oven creating a ledge on which creosote will sit and be diificult to get at no?
4. If I cannot attach brick or stone to the flue itself then I will have to put my non-existent bricklaying skills to work to somehow fashion a chimney ?
5. do I use refractory cement for tge whole chimney and the bottom edge of flue sitting on oven?
6. I suppose I need to do all this before applying perlite/concrete to dome?

Is this is all correct or do I start by building the chimney out of brick and build two pices of angle iron into brick to hold the flue thereby eliminating need for flue to sit on top of thos columns and on top of stove?

How the heck do I seal the bottom and top of chimney between flue and chimney wall - just with bricks and refractory mortar?

Offline stonecutter

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Re: WFO Construction - stuck on two things
« Reply #17 on: July 12, 2014, 08:32:06 AM »
You don't need to insulate the flue liner.....you just need to keep masonry away from it.  The insulation allows you to build up without worrying about maintaining a cavity, nothing more.


I think you should keep it simple and run a single column of firebrick on each side of the oven opening. Then set an angle iron across to create a ledge for the flue.  I don't see a problem with the flue being supported by the oven on one side, as long as there is no insulation under it.

The other option  is to use a stainless flue, then you don't need to worry about structure around a clay liner.   Then all you need to do is basically build a square or arched vent to attach a transition plate, then your flue. I feel this will be a lot easier for you.
« Last Edit: July 12, 2014, 08:45:45 AM by stonecutter »
When we build, let us think that we build forever.
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Offline SC

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Re: WFO Construction - stuck on two things
« Reply #18 on: July 12, 2014, 12:05:14 PM »
If I run up two columns of brick as suggested, can it be regular brick or does it need to be fire brick? I bought a bunch of red reclaimed brick. I would think i am going to be OK for heat outside the oven no?

I went out and got the granite flags. You are right they are very heavy. I do not have sufficient room on the base at the back for much perlite/concrete (I have 4 inches between the lathe and edge - so maybe room for 2 inches).  So this has me thinking again about a couple other options:
- I read about pencil rebar. Basically plant one end in the granite then bend it over to the roof other side and plant that end. Repeat with several other pieces. Like an umbrella frame.  If I did this could I get away with less covering over the insulation before laying the stone? Could I use just Portland or should i do the perlite?
- alternatively, just put the granite veneer on the vertical sides, so I could get away with regular mortar (maybe with the adhesive you suggested), then forget about flagstone on the top - stucco the top down to seal against the veneer on the sides. If i went with white i would probably have to have white grout between the flags on the sides. So sides in granite flags, top in stucco.

Offline TXCraig1

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Re: WFO Construction - stuck on two things
« Reply #19 on: July 12, 2014, 12:06:56 PM »
It's time to ban iphone photos.
"We make great pizza, with sourdough when we can, baker's yeast when we must, but always great pizza."  
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