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The rest of the (WFO) Story

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OldWoodenSpoon's picture
OldWoodenSpoon

The rest of the (WFO) Story

Okay, after all the compliments and enthusiasm over my new WFO, it is time to tell the dirty details of something I only just touched on in my earlier blog post:  the little matter of too much fire too soon, and the problems with the doorway arch.


Saturday morning I got over enthusiastic throwing wood into my "small drying fire".  My wife admonished with "Isn't that a little big?", to which I replied in my best know-it-all tone "No honey, you should see a big fire!".   Then we noticed the cracks, and the top bricks of the arch sagging from thieir proper position.  After much running around for steel buckets, fireplace tools, water and my heavy elbow-length gauntlets (it was really hot in there) I shoveled the live fire out of the oven as fast as I could and doused it with water in the bucket.  It was too late though, and the damage was done:



The crack is not all that bad, but the brick problem is another story.  A couple of days earlier we had noticed these bricks had come loose.  When I investigated, the mortar and the bricks had all separated from each other and the mortar was just loose slabs between the bricks.  This next shot makes it easier to see both the loose mortar and the keystone brick dropping through the top of the arch as well as a head-on view of the crack.


 



 


I hoped the insulation layer would secure things together, but the heat expansion in the dome proved I was just wishful thinking.  Something had gone wrong somewhere and my arch was coming apart as I stood there.  You can see the tops of two bricks I wedged into the arch to hold things up while the oven cooled off and I figured out a plan.


 



Here you can see my solution, if you look carefully.  I hope we can get a better shot of this tomorrow when the light is better, and I will edit that shot in here if we are successful.  However, if you can see it, my solution was to break another rule about ovens:  I installed a metal arch support in the form of a hoop shaped to fit inside my arch.  I made the hoop loose fitting, and then loosely packed a wood stove door gasket made of a fireproof, non-volatile glass fiber between the hoop and the brick to take up the slack and provide compressible space between the hoop and the masonry.  These materials expand at different rates and to different extents, and I have no idea if this will work or not.  Since my alternative if it fails is to rebuild the arch, and my alternative if I don't try this is to rebuild the arch, this is a free chance to get lucky.  As you can see in this shot above, I pulled all the old loose mortar out of all the arch joints.  That's all it took too:  I just grabbed it bare-fingered and pulled each wedge out in one piece.


While working on all this and running around I noticed something I now call "probable cause".  Earlier, I blamed this whole incident on too much fire in a green oven, too soon.  The next shot proves I could be wrong about that.  It certainly was contributory, but I'm not sure it was the cause at all.  I think I made a bigger strategic error earlier in the building process, in how I joined the arch and the dome.  If you look carefully at this next shot, especially at the very top brick, you will see it is tilted up to the right.  This brick was dead-level when I built the arch.



Here's what I did and what I think happened:


- When I mortared the arch originally I only mortared the front 75% or so of the wedge-shaped gaps.  I left the rear 25% empty so I could tie in the oven dome itself.  This was, I believe, the fatal flaw.


- As planned, I built the dome and filled in the rear-most 25% of these mortar wedges in the same pass as building up the dome, effectively making those parts of the arch an integral part of the new dome.  I also added a layer of oven mud over the top of the back 25% of the arch as well, thoroughly integrating the arch and the dome.


- I sat back and watched it all slow-cure as I kept the dome and the dome-arch joint draped with moist towels for three or four days, and then under cover of dry towels for two or three more days, all to slow down the surface drying and let the inner clay keep up better.  During this time the new dome showed some stress cracks from drying, which I worked over with the back of a spoon as much as I could to try to iron them out.  Honestly, it did not help much, and my overzealous drying fire on Saturday morning brought them all back.


Now, look again at the tilt up-to-the-right of that top brick in the shot above.  I believe the oven dome shrank significantly in drying, and because the doorway arch was so throughly integrated into the dome, the dome squeezed the arch in on the sides and down on the top at the back edges of the arch bricks, popping all the mortar loose and opening up bigger gaps between bricks than were there when I built the arch originally.  When the arch alone was complete, the inner surface was continuous, with the inner edges of each brick neatly and firmly in contact with the edges of it's neighbors.  Now it looks like carved jack-o-lantern teeth.


The fact that I built too hot and too large a fire on Saturday only brought all this to the fore sooner.  I now believe I doomed this arch when I tied it so tightly to the dome of the oven.  Nothing I read told me I should do this, and it also did not tell me I should not.  I learned that part myself.


I installed the new metal arch support today, and also re-mortared the arch.  Now I will give the fresh mortar in the arch a couple days to dry out and go back to small (yes, really small!) drying fires to slowly cure the oven dome and all, and see how it goes.  When I am finally able to really heat things up I will find out if my metal arch is going to be a help or the final straw that destroys the doorway arch.  Then I will know what the next chapter will be.


Thanks for listening, and stop by again.  I'll continue to post my progress, positive and negative, right here.


OldWoodenSpoon


 

Comments

Mebake's picture
Mebake

Sorry to hear that you had to go through all the trouble, but it must be worth it,ultimatley.


Can't wait to see your first ever WFO born loaf!


khalid

SylviaH's picture
SylviaH

But don't get discouraged.  My daughter had the stone masons tear down her WFO 3 times before they got it right..the best part was it was done during the just beginning phase and that was only a fraction of the stonework building the house, the builder said he knew how to build a wfo..well my daughter and I did a lot of research..the worst, 1st mistake was, they put the flue in the oven..like a homes fireplace...yikes!  Speaking of flues, since you may be redoing the arch...I see a lot of wfo without one...they difinately have a good purpose and keep that heat and smoke off that lovely arch.  Since you have to redo some arch work, you might consider a flue installation.  The whole inside of her oven is done by joining firebricks into a dome shape...lovely work..I don't believe there was even morter used..just skilled brick masons.  I hope I'm not affending by asking but you are using a special mortor for heat..like they make the cement floors out of in some wfo's..that seems maybe the type that would hold up best.  I know that while building her wfo oven they said that the mortor eventually would just drop out of the stones if it was used in the dome.  The main reason I dropped in my 2 cents worth was just, if you have to do some work over...I think you would see benefits from a chimney flue..by the way it's installed on the outside of the oven door : )  My first fire consisted of only balls of newspapers.  The fire your showing in the photo did look a little large for the first firing..maybe it could have been about the 4th to fit the size of your oven.  The whole oven takes quite a while to dry completely before firing and this curing needs to be done again, before using a finished oven if you live in a very cold climate. 


Keep up the good work and don't get discouraged...you certainly are to be commended for starting such a project.  Added:  I have an arch very similar to yours except the opening sides are straight with 1/2 bricks, with the flue behind, going up to the top where the bricks arch..they are only decorative.


Sylvia 


 

OldWoodenSpoon's picture
OldWoodenSpoon

I'm dissappointed obviously, but I'm doing okay.  It helps that this is a "test oven" of sorts.  This is a mud and earth oven a la Kiko Denzer, and using his book "Earth Oven" as my guide.  The only brick, mortar and stone in the entire project above the oven floor is in that arch you see out front.  The rest is all fireclay, sand and water.  That is probably one of the reasons it expands and contracts so much with heat.  It also means there is even more water in the dome than you would have expected if it were a brick dome covered in grout or mortar.  This is a full 5 inches thick of clay and sand.


  This oven will (I hope) last me a few years, but eventually I will tear the oven off the top, saving the foundation, and build a "Pompei Oven" in the style of what your daughter has.  Mine will not come out so fine though, because I cannot afford to hire a mason, so I'll do the work myself.  I have all the experience in bricklaying that you see on display here!  None!


Thanks for the tips on fire size too.I'm going to go back to step zero and start again as if I'd never lit it up, once the new brick work drys out for a day or two more.  I cannot undo the damage done, but I can sure hope to not cause more by over-firing it again.


I considered adding a flue, but decided this was simpler to start with.  If I end up having to rebuild the arch, I will reconsider that option.  If I can cut some bricks so I can put the flue right on the front of the arch, I may try it since I've now practiced and learned on a couple of arch builds already. :)


Thanks again for the support!
OldWoodenSpoon

SylviaH's picture
SylviaH

Your oven looked so good I honestly thought it was made of stone..and you were to yet finish the outside last layer decorative.  That's some great looking sand and clay work!  Looks like cement.  I'd say you could do anything you put your mind too.  As far as my daughter's wfo well that's another story...I meant to express the work and disappointments that come with even the best stone masons ....and there are very to be found.  I think you have the makings to do just as good a job as a trained mason.  I had to learn all about making a fire...I thought you just threw some logs in arranged half way decent and lit them...now I know how to start a proper fire and without all that smoking...the first fire we lit the fire department truck was seen checking the neighborhood..though they didn't bother us...I'm sure someone must have called...the smoke was terrific and we just seemed to keep making more...we did get a bit of laugh out of it...though it's not funny for the fire dept.  I know when that first pizza or loaf comes from your oven...you will have a good long laugh and big smile of satisfaction!


Sylvia