Structural Slab for new WFO

[mikku]

Re: Structural Slab for new WFO

So--fill the void with castable..no cardboard.. its only 25mm thick--so trowel grade, casting grade..either OK? Got open bags of both?

[david s]

Re: Structural Slab for new WFO

The 1:5 vermicrete is not really strong and will abrade easily when you slide the pipe in and out. I overcame this problem by making a stainless steel sleeve around the outside of the pipe, but mine is single not double. Yours is more complex being double. It has stood the test of time well, whereas I'm sure the 5:1 vermicrete, which surrounds the sleeve, would not have.

[mikku]

Re: Structural Slab for new WFO

Thank you! I had not carried the chain of thought to your final conclusion. Have to go back to my "bankin-ya-san" sheetmetal friend and mooch another piece of .035 stainless. I know he has another piece that will fit this situation, because he cut off pieces today for my caps! Getting good at mooching but I have to wait now for his (in-return-free-requests!)

Think twice, twice--then cast once!

[mikku]

Re: Structural Slab for new WFO

Started setting up the chimney for refractory lining.

Cut a cap from .035 stainless sheetmetal, this stuff cuts wierd--even with what I thought sharp snips, does not cut cleanly, likes to roll instead.

By making some tabs, I could inset the cap about 30 mm into the end of the pipe end and then pop-rivet into place both inner and outer at bottom of pipe.

I did a little calculation on the volume of the pipe at 25mm thickness and was surprised with the amount of refractory required. I don't have 28 kg of materials and really don't want to buy more either! Sounds like a SOL situation!

Sure hate planning something and have to change in midstream. What now?
Then I thought about my house chimney, and the one that Laurentius has in Chiba. Mine is insulated with something, his is double-wall with air-space. Both using insulation rather than refractory--like a masonry chimney would have as a "flue liner"..

So plan change --fill the void with loose fill perlite! I have enough of that and don't have to buy any more!

So, I put a fine bead of "silicone" in the small space at the bottom section of the pipe--to keep the perlite from falling out, and filled the space. When I got to the top, put the other cap in place and riveted only the outside. That way, if the inner flue expands in length, there are no rivets attempting to stop it.

Finally, capped the top off with trowelable castable. I am assuming that it will shrink enough while setting up--to allow a gap for anything to vent on heatup or cool down.

Next time I have a chance, I'll flip the chimney end to end and fill the bottom 30mm void with refractory to seal that off. Got to assume that the silicone will burn up when the first fire is lit, or I can carve as much out as possible before putting the refractory cap on the bottom end.

I expect the chimney to be a little cooler, possibly enough not to worry about burning yourself when it is firing. The flue should heat rapidly as soon as the fire is started and create a good draft. At least those are my hopes right now.

If it doesn't work properly, I can always drill out the top pop rivets--break the refractory, dump out the perlite and fill it with refractory--but that is another $30 for a 20KG bag of the troweling stuff.

Pictures are below:

[david s]

Re: Structural Slab for new WFO

If it was mine I'd be drilling a small hole through that refractory collar. You don't want it totally sealed. Remember that a litre of water creates around 1600 litres of steam.

[mikku]

Re: Structural Slab for new WFO

I did not mix any portland cement or water with the perlite (just loosefill) when insulating the stainless spiral duct. However, the refractory cap shows no sign of shrinkage after two days. I used stainless pop rivets, so they should anchor the cap-preventing it from falling out.

I agree, with the venting --but probably will be drilling through the outer 200 mm right below the cap in a few places. If there is any residual moisture it can vent, also probably a bad idea to cap both ends (without some kind of relief exit)--all the makings of a pipe bomb when the air inside expands!

Thanks for keeping your sharp eye on my project!

[david s]

Re: Structural Slab for new WFO

Yes, a hole through the outer pipe is probably a better solution. You only need a tiny one.

[mikku]

Re: Structural Slab for new WFO

I agree, That is what President Obama refers to as a "Vulcan mind meld"!


I got it right..he was close!

[mikku]

Re: Structural Slab for new WFO

Time is rapidly approaching for the oven to be moved outdoors to begin heating the refractory and forcing any residual moisture out of the pericrete. Alot has been written about brick domes, what would the firing schedule for an 80 mm thick cast dome look like?

It has been three months since the original casting and well over a month since the pericrete insulation was placed. Everything looks bone dry right now--accompanied by several hairline cracks on the render.

[mikku]

Re: Structural Slab for new WFO

Finally had a chance to make up a sleeve to surround my double wall DIY chimney.

The chimney is 200mm diameter, so I fabricated a sleeve out of .035 stainless stock to be 216mm diameter and 400 mm high.

This will allow for my chimney pipe to be removed and still leave a chase that will not crumble. (per David s recommendations)

Now, the pericrete can be formed around this sleeve and later the entire oven can be plastered.

Used drill in anchors to attach my baseplate to the refractory and popriveted the sleeve to the baseplate prior to attaching.

Found a small can of furnace cement to make the seal- stainless to masonry and gobbed the rest of the can on top of all the flared flange- sleeve.








Could probably bring the oven outdoors now to do the curing fire or pile some more pericrete around the chimney then bring it outdoors? Depends on the weather now. Just had a typhoon go through this week-end, so glad the oven was indoors.

[david s]

Re: Structural Slab for new WFO

I can't find the firing schedule for the castable that I use, but from memory it is 25 C/hr to 300C then 50 C/hr from 300 C to 500 C then again 25/hr from 500 C to 600 C, 50 C/hr from there on up to 1450 C. Obviously you won't have to worry about these higher temps. If you try and follow this schedule using wood it will not be easily achieved due to the poor control you have. Suggest you read the curing thread for an alternative, which we are not allowed to discuss. The biggest problem you face is driving out the moisture gently. If you see steam then you are going too fast, back off. Try a search of your product on the net for their firing schedule. I've found most steaming problems (blowing) with pottery occur at around 250 C. I should think that castable would be the same. Do not think that because you are over 100 (boiling point) that it is safe to increase temp rise suddenly.

[mikku]

Re: Structural Slab for new WFO

I am at the point of ordering thermometers, both for the oven door and an IR thermometer to measure firing temperatures. I had the order all typed in and the items cannot be sent to Japan using amazon. If I search amazon, jp; I am having difficulty finding anything. Must be some restrictions on lazer or IR in this country. I'll have to try some other sourcing to see if I can find something somewhere.

I am trying to locate items that would allow me to do a more controlled firing, so far with no luck. There is no real rush to get this oven completed, it is more important at this point to do it right. So I will be taking my time more....

The place where I located the furnace cement was really surprised to see that someone in this area was actually building a workable pizza oven. Their business sells imported wood stoves, accessories, and chimneys. When I showed my pictures, people gathered around and asked questions for about an hour.... I was really surprised with the interest shown. A wood fired oven is called a "kamma" in this country!

The list is growing of people who want to see my oven in operation. This summer sometime will be the date to shoot for.

Thanks for the firing information and everything else!

[david s]

Re: Structural Slab for new WFO

Be careful when using an IR thermometer. It reads the surface temp which will be higher than that which is deeper in the walls, hence the slow temp rise required. Water in the refractory will hold down the temp wherever it is present. You've reached the exciting part- FIRE !
Good Luck.

[mikku]

Re: Structural Slab for new WFO

Ran into a merry-go-round circle jerk this week.

Since I could not get the IR thermometer I wanted via Amazon--because of import restrictions, I ended up buying one threw my hardware store. Today when I got some commercials from Amazonjp, the product I had been looking for before was now available here at a competative price. Now I have an off-brand IR thermometer for more expensive than a brand unit!

I was able to locate a good quality oven door bi-metal thermometer and that is now on order.

Since there are a few things waiting to arrive--decided to add the rest of the pericrete insulation around the chimney sleave--that turned out being a lot of monkey business as well because it had to be stacked 16" high and it tapers from around 5" to 2" thickness at the top. Free style insulation--now the oven begins looking like some outer-space ant hill. This insulation was 5:1, perlite to portland--should be a little firm tomorrow, but fragile.

I looked at several different LP gas burning devices, ones that would be used for outdoor cooking (circular burner rings), replacement oven parts for commercial ovens, and weed burners. The weed burners are available with different tips, orifices, wands, and hoses. I decided that a nice item for starting the wood fires without newspaper--etc could be used maybe in my initial curing as well. I'll be ordering the smallest orifice size, using .4kg LP/hr. Should be able to throttle that down as well. I guess enough said on that subject, agree that I should be able to get controlled temperature curing with this process.

Attached are the chimney cover insulation--after the curing process, the entire thing will get a render and some type of final water/repellant coating.

The insulation around the chimney actually does more to insulate the landing area. The chimney doesn't need the insulation--it is already insulated; once the render is in place, it will give a lot of support for the chimney.

[david s]

Re: Structural Slab for new WFO

That little thermometer you have in the oven is exactly the type I use. They are cheap, accurate and you can read the temp where you need it. Do yourself a favour and pop rivet a larger base on it. When moving it around the oven with the existing base they fall over and are difficult to manouevre.