Structural Slab for new WFO

[Laurentius]

Re: Structural Slab for new WFO

Hi Mikku,

Kamogawa is a big Japanese tourist destination, we have flower center, Sea World, Temples and many places of interest. Surfing in our town and down the coast is great, they have major competitions here. We get road cyclists, motor cycle and car tours, bus tours. The hospital where my wife works is so renown that it gets international medical tours.

[mikku]

Re: Structural Slab for new WFO

But you can do and see all those things year-round. Why early up and out for you when tourists are here?

[Laurentius]

Re: Structural Slab for new WFO

Think? To avoid it! To get the things done, before they get here, they go to supermarkets, places we local use daily and if we get there early we don't have to deal with the mobs or the traffic.

[mikku]

Re: Structural Slab for new WFO

Ah So!

That is why I live in the sticks! No crowds around here, biggest gathering is at my neighbors farm. 200 head of milk cows! That is a real crowd and you can tell when the barn is being cleaned! Lots of fragrance that floats thru the air!

Most of the houses around here are besso's (vacation homes), so this week there will be people mulling around pretending to enjoy nature. The rest of the time -- quiet! The way I like it!

[mikku]

Re: Structural Slab for new WFO

How is the breadmaking going these days? Now with some warmer temperatures, it should be a little easier getting the dough prepared and raising??? The whole neighborhood should smell good when you do a big batch of sourdough? Someday you'll have to send me a loaf of your specialty bread...so that we can enjoy what you are famous for making! maybe you can send it "japan style COD"...I cannot remember the term ---"dai-biki" or "chucku-balai", something like that?

[mikku]

Re: Structural Slab for new WFO

I took a day off today--really was supposed to work, but the job will not be finished--with a Sunday workday. (National Holiday - Children's Day)!

Since I was playing hookie, had to make the day productive--up at 4AM to unload the van and drive to the mountains to pick up spring water for drinking, got about 80 gallons.

Back by 7AM, early Skype to USA, early mooching of the forklift from my neighbor and was able to jockie the oven outdoors onto the lawn. By USA standards, postage size plot of grass!

Had some cut offs from structural beams so blocked up the oven a little and just set it down on the grass. It is elevated about a foot! Good enough to do a curing test burn.

I was surprised, the oven drafted pretty well! Only time smoke billows out of the door opening is at start up and when the active flame changes to smoldering. Otherwise, the smoke finds its' way up the chimney and so far, no staining on the stone around the oven opening.

Started with a very small fire, but kept it burning most of the day--adding thumb diameter size pieces of oak and gradually got up to some 1 1/2" pieces right before dark.

Got a lot of cracks in the pericrete and render. Actually looks like a "google map" that plots the location of techtonic plates round the world! But no cracks to the castable refractory! I guess the water has to get out--shrink, expand--whatever it does, but so what! When I finally get all the water out, it should fire great and then I can do multiple render coats over the outside and add wire mesh to prevent future deep cracks!

Think today was a "good day", glad to be busy with work--makes off time just more precious!

Attaching some photos: Ended up putting a potato wrapped in aluminum foil to see if it would bake, Probably hot enough--but did not keep it in long enough.











As you can see, the insulated chimney was also performing great.. Just slightly warm to the touch--it is also removable for transport via forklift.

Tomorrow is supposed to be clear as well, so in the morning--I'll remove the chimney and cover with heavy tarp--keep it dry until the next time I get some time off to burn it again!

[mrchipster]

Re: Structural Slab for new WFO

That is a beautiful looking outer arch.

Chip

[UtahBeehiver]

Re: Structural Slab for new WFO

Mikku,

Looks like a temple entrance to your oven, the stone, can't remember the name, really looks nice. Great job on a cast oven.

[mikku]

Re: Structural Slab for new WFO

Thanks for the compliments.. However, now I am having some second thoughts about the design itself. Most people use some kind of ceramic fiber over their oven domes OR loose fill. I think there is a flaw in thinking that pericrete directly over a cast oven is correct.

Pericrete is brittle on its own, and the castable sections of the oven will expand slightly with temperature. The pericrete has nothing to do except crack, and will probably continue to crack everytime the oven is heated---

I am thinking of removing the render, recycling the pericrete and putting something flexible or something that can absorb some of the expansion between the dome and the pericrete/ render coat.

Or second thought is to scrap the dome concept entirely and make an enclosure.
Only thing that is lost is whatever materials were in the render coat--which is minimal. Pericrete can be broken up and used as loose fill.

Got lots of time to decide what to do about this situation. Now the WFO is outside, I started setting up pipe scaffolding around the oven--later it can be tarped better than it is right now. Cannot rely on weather forecasts. All week here was supposed to be sunny to cloudy. At 4PM downpour, lightning and thunder...after that sunny until the sun set! Lucky i covered the oven with a good tarp this morning before going to work!

Happy to see that the oven fired and vented fine. Also rethinking the "Oya Stone", it is turning out to be extremely soft. Probably look like crap after a few firings and moving cooking utensils in and out of the oven!

This is a real good learning experience. After a few of these, might end up with something totally functional!

[david s]

Re: Structural Slab for new WFO

I'm pretty sure your cracks are caused by not allowing the vermicrete layer to dry before rendering over it. From memory you plastered over the vermicrete about a day or so after placing it. This locks in the moisture. Now when you fire the oven you are making steam which is causing the cracking. See advice on post no. 60. Don't worry too much though, you can still plaster over it all once it's dry. If you are having trouble eliminating the water, try drilling lots of holes through the outer shell. Also throw some plastic sheeting over the dome to test if water condenses under it. This will tell you there is still water in the insulating layer.

[david s]

Re: Structural Slab for new WFO

The other reason you have lots of cracks is that your first fire was kept going most of the day. I suggest you read the curing thread. The temperature ramp up should be done slowly. The vermicrete layer does not matter that much but you don't want to stress the refractory castings. The top of your dome will dry first while the base will still be wet. This creates an enormous difference in temperature between the two which in turn means an enormous difference in expansion of the material which can lead to cracking. Because you have wet vermicrete sitting directly against the hot refractory then steam will be produced easily. Folk who use blanket have a buffer which prevents the vermicrete getting too hot too soon.

[mikku]

Re: Structural Slab for new WFO

Thank you for your observations. I have a couple of questions maybe you can fill me in on.

1) What is the history of pericrete--i.e. who started recommending using it?
2) Are there any commercial oven manufacturers who use pericrete in their product that is sold?

A couple things about me--you probably know by now, that I am not a patient person, but I think that I can produce quality products--not necessarily WFO's--but in the other things that I do.

I think that this design is flawed--because there is nothing that will absorb the expansion of the refractory when pericrete is in direct contact. Please correct me if I am wrong!

The render coat that I did, was relatively thin--approximately 9-12 mm thick on the dome itself, but it was rock hard. It takes a lot of pressure to make cracks in that!

I really do not care of the pericrete cracked now in initial firing--or the render either.. Yes it can be covered again. But when the oven is "dry", refractory still expands when heated--and the same situation still would exist. Nothing to take up for the expansion.. That is what I am concerned about! I do not want to be rendering over and over until the cows come home.

A few people around here are interested in WFO's like mine, but I told them--I am not interested in selling anything that I do "Until" I get the bugs worked out!
And if you make more than one, you can't be waiting around for pericrete to dry out! So looks like trash that idea altogether.

I know that you have made several ovens, I do not know if you have sold any to other people... I would rather give them away for free than to sell one and get continuous call backs because of avoidable design flaws. Just not worth it. In house building, I try to avoid bad designs OR if it is an architects' project, I alert them to what I see as potential problems. Then, I am half "off the hook" if something does go wrong.

I noticed when firing, that the top of the oven "pericrete" felt very warm to the touch--also areas where cracks appeared were hotter.. Da--direct path to refractory! Most of the other areas including the chimney were rather cool. The IR thermometer did not give readings over 200C anytime during the day... Most of the readings were in the mid to upper 100 range. Hottest area was the top of the transition--where smoke and heat exited before going out the chimney. Never was the fire anything near roaring..usually flamed up and then went back to smoldering embers when the easily combustible fuel was spent.

Cannot see any damage to refractory that was poured in January and able to withstand temps to 1450 deg. C. Really thought that it was a slow burn! Sorry if I sound Irish!

Anyway, yesterday was my only day off for a while--have to jerryrig some decent cover so the oven does not get soaked! Thanks again!

[david s]

Re: Structural Slab for new WFO

Perlcrete directly against the refractory does work, but it needs to be dried out. See my PM

[mikku]

Re: Structural Slab for new WFO

Got home early enough from jobsite. New house is near Honda automotive manufacturing- Kiyohara. There are alot of "just in time" suppliers located in the same area--so there is a real rush of traffic in the mornings and repeats around 5-7 every day. If I get to jobsite before 7AM then rush is avoided--if I try to start like normal people at 8AM (takes 2 hours) to travel to site vs 35 minutes. Dah! Start earlier...

Tonite was second burn--for curing (no rhyme or reason) but this time the insulation layer of dome was cool to the touch and so was all the render.. Sunday's burn must have driven a lot of the moisture out.. Castable refractory showed no signs of distress -- maybe a few more burns then "light it up for real"!

No new cracks on pericrete or render--must have been like you said --Davids--water has to get out, and steam builds pressure.. Relief valve are the cracks!

This week-end, have to see how high of a flame I can get roaring out of the chimney--see if stainless melts! Whoopie!

Lots of short; dry, pine scraps from jobsite too! --good to get an initial bed of coals then go for the good stuff--dry oak or ash!

[mikku]

Re: Structural Slab for new WFO

Tonight, repeated yesterdays' routine. Started with some kindling that started almost immediately when you put fire to it. Monster took off burning right away. Added a couple of pieces of oak and let it burn --most of wood was consumed in flames--but right before going to coals, pushed everything to center and rear. Whole flame pattern changed--instead of flames licking forward--now the tips pulled to the rear and washed the dome with their tips.
Even the coals began to glow more brightly. The oven was drafting real nice and only hot vapors were being emitted from the chimney!

Nice to see the oven burn so clean. Even the pericrete and render stayed cool..must be an indication that the moisture is beginning to be drawn out. have to do the same tomorrow. A nice chicken might cook now, but chicken in one piece is a rarity in these parts. You can buy dressed chicken breast (8 nice pieces- 2 KG- for $4.50/pkg) but if you can find a scrawney chicken in one piece--they want $12.00 for this bird! Rather buy a slab of pork loin for the same bucks--Have to figure out how to do one of these in a WFO--in slices deep fried....I know the routine.