Structural Slab for new WFO

[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

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.

[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

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


I got it right..he was close!

[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 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

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

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:

[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!

[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

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

Hello david s!
Both the 150 and 200 are .5mm thickness, the T-collar is .8, and the flat piece it is spot welded to is 1mm.

Are you saying that I should try to line the 200mm with a layer of corrigated cardboard? and then slide the 150 inside? And then fill with refractory?

Is there a problem with a crack in the refractory anyway? Some chimneys are double wall with only air in between?

Corrugated is probably too thick. You need it between the refractory and the inner pipe because that's the one that gets hot first. Maybe it doesn't matter if it cracks as it is only acting as a spacer between the pipes. It is a different story if it is the structural refractory of the entry though. If you want the pipe removable then making it slightly loose will be useful. You only need about 1mm thick for this.

[mikku]

Re: Structural Slab for new WFO

I was planning to have the chimney removable. The 150 simply sides over the T collar. I was going to build up around this chimney with pericrete.. (possibly 30 cm height )..maybe 5:1 to give the whole thing a little support/ but wrapping cardboard around the 200 before stacking up the pericrete. Final coat would be the render and whatever else--maybe the lime plaster or shikui as a weather coat. The cardboard could burn out or pull out with the pipe removal. I am assuming that the 5:1 would keep its shape after several insertions and removal operations. I could fabricate a water collar that would clamp around the 200 --maybe a simple "T" out of 200 stainless to cap things off. At the top of the dome, I still want to leave a breather vent to get rid of steam in the future. Cannot figure out where to locate a "dip stick"--Maybe "Brickie would kindly tell me a good location"--hehe! lookout now!

[mikku]

Re: Structural Slab for new WFO

Hello david s!
Both the 150 and 200 are .5mm thickness, the T-collar is .8, and the flat piece it is spot welded to is 1mm.

Are you saying that I should try to line the 200mm with a layer of corrigated cardboard? and then slide the 150 inside? And then fill with refractory?

Is there a problem with a crack in the refractory anyway? Some chimneys are double wall with only air in between?

[david s]

Re: Structural Slab for new WFO

I used castable refractory around the single walled stainless flue pipes for the second and third ovens, which were identical, that I built. In both cases the refractory cracked in the same place. I concluded that the expanding pipe, which is going to get hotter way faster than the refractory that surrounded it was powerful enough to fracture the refractory. The pipe in both cases was fairly thick at 0.9 mm. I now use 0.55mm which may not be strong enough to stress the refractory to the point that it would crack, but I was not prepared to take the risk so now always make sure that there is a slight gap. You can do this by wrapping thin cardboard around the pipe before casting up to it, then remove the cardboard once the refractory has set. You don't say how thick your pipe is but this may be a consideration. Ready made pipes are usually pretty thin stuff.