Structural Slab for new WFO

[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.

[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.

[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!

[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.

[mrchipster]

Re: Structural Slab for new WFO

That is a beautiful looking outer arch.

Chip

[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!

[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

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!

[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

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

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

The only holidays I take off are 4th of July, Christmas, Easter...if I have other work to do.

What ya mean...tourists are here? What has that to do with you? Are you turning Japanese and gawk at foreigners? Even the little kids stare and point their finger at me as their mothers tug them by. Or are you too acclimated and blend into the crowd?

[Laurentius]

Re: Structural Slab for new WFO

Hi Mikku,

Sounds like you had some productive fun. Today's a holiday and you're not off. Its a stay at home or get out early day for me. The tourist are here.

[mikku]

Re: Structural Slab for new WFO

Back to the hunting and gathering mode. Had a day off finally from work, decided to try gathering wood for WFO and wood stove. The oak that was cut down about 3 years ago was my project for the day.

Three years is way too long to leave good wood lay on the ground. Spent 5 hours with a professional Echo chainsaw cutting only one log up into usable firewood and transporting it back to my house.

The log started out being 4 meters long, varying in diameter from 750mm to better than 600mm. The insects and weather had taken their toll. Mushrooms were growing on the bark, a real sad story for a once stately tree.

I did my cuts from both sides--very hard to get a cut to line up side to side for a relatively big log. There were other logs jammed around my log of interest.

Finally got the log cut up into 350 mm blocks and then the big job...slicing off all the bark and trying to get down to undamaged wood.

Better than 1/3 of the wood was too far gone. The rain, insects and other wood diseases had damaged much of the wood. I am lucky that this year, I began to harvest firewood from this tree. Another year would have made firewood an impossible option.

At least, I got maybe a ton of firewood off one log. I hope the sun can do some good with this wood. The stuff I transported is free of bark and the diseased wood has been surgically removed (chainsaw style).

Now when I get my next day off, I can begin splitting it into burnable sizes.

[mikku]

Re: Structural Slab for new WFO

That is the exchange I got for little snow. Tochigi prefecture has a lot of Sugi trees and their pollen bloom is mid March. When the wind blows, it looks like green smoke---and the trees are everywhere. Even taking allergy meds, nose is running like a hose, sneezing, eyes itching... Now we are into Hinoke pollen time, I'm not as allergic to Hinoke so the meds keep life manageable. With the Sugi pollen landing on everything, you need to use your windshield washer to clear the windows.. What comes off looks like split pea soup, but creamy no chunks! Better than the icy winds though.

This year in Northern Minnesota they are worrying about the ice being off Lake Vermillion for fishing opener--that is sometime the beginning of May--I think.
One year ---many years back, there was still ice in the harbor in Duluth the first week of June...burrrrr.

After the snow starts melting then watch out for flooding all along the Mississippi river! If it isn't one thing, its something else!