Matt Todd

I've had these growing from cuttings for 4 or 5 years now in zone 5b. I hear they are difficult from seed. I think you'll get vegetative growth every year, and maybe your colder zone will keep it more in check! As you've read on some of these other comments, it can very easily get out of hand but it's enthusiasm is limited to early June to frost here. Maybe more limited where you are.

But what I really want to say is: curb your expectations on fruit. Even IF you get it in your zone, this passion fruit is not the same as its southern cousins. The "fruit" is limited to juicy pulpy pouches surrounding the seeds. You can mash out some pulp from lot of fruits to get a little bit of goodies. Not worth much. Generally I just bust one or two open a year to chew on the pulp and spit out the seeds.

While the fruit is nothing special, it's still a fantastic plant for the flowers and medicinal leaves! Even great to grow as a seasonal privacy screen.

Some fine looking dragons there. My own cat is anxiously awaiting her mass heater, soon to be installed.

Where do you suppose that black water drip comes from? I would have thought she'd be entirely dried out from the last heating season!

Is this a yearly issue of masonry absorbing ambient moisture from humidity over the summer and needs a few burns each new cold season to dry it out again?

Fox James wrote:Sounds good apart from putting super wool in your oven, that is not a good idea due to the risk of microscopic fibres being ingested!

Super wool is the mineral based safe alternative to Kaowool and Ceramic wool. I would still probably rigidize it though! Or perhaps use vermiculite board.  

Taking all your comments into consideration, I'm going to go with a silicone carbide kiln shelf. Thinner and stronger than the standard cordierite shelves with better thermal conductivity (only con seems to be a higher price!)

I will surround this with a steel box for the oven. When I'm not using the oven, I will leave a piece of superwool blanket on the oven floor for better firebox efficiency.

Hopefully this will give me the best of both worlds: a quickly heated oven that is powered by both the firebox below and the hot gasses in the top of the bell. The Shorty core will allow for adding wood if I need a longer cook time and the thermal mass of the bell should ensure longer useful cook time.

I acknowledge that this is all experimental and unproven but I'll give it a shot and report back!

Cristobal wrote:
Regarding the white oven, please be aware that it may not work as you wish. Usually white ovens are made from steel or cast iron and are used while burning.

You're absolutely right. Last night I did a test on a 1 inch thick slab that I'd made from extra refractory. I used a very powerful propane torch to blast the bottom up to 1000F degrees (538C) but the top never got above 190F (99C.)

Extrapolating that into the firebox, the slab bottom would never get anywhere near 1000F from woodfire alone and with the actual slab at 2.5 inches thick... it would never truly heat up to anything close to a usable oven temperature. And like you said, the brick side walls would not pick up enough heat from exhaust gasses alone.  Perhaps it would reach an operating temperature if I continuously burned wood all day long but that's not desirable to anyone.

So now I'm thinking I should replace the refractory slab with 5/8ths kiln shelf (since the slab is TOO massive to conduct heat) and top that kiln shelf with a steel box oven. This would give me heat conducting up from the firebox and also heat from the sides/top via the exhaust gasses.  Quick heat response is good, I think. If I'm cooking something that needs more oven time, I could just add a log or two. Does that sound like a more reasonable design?

Cristobal wrote:
I do not want to be negative, just want to share my findings.

Not at all. This is why we post here, so others can provide feedback and save us from mistakes!

Cristobal Cristo wrote:Matt,
Actually the thinner kiln shelf is exposed to less breaking forces.

Your slab will store more heat. Are you planning to make it a black or white oven?

Good to know!  I was majorly concerned about both the uneven heat and heavy items on top of a suspended kiln shelf (however heavy something like a full casserole dish could be.) But if you're successfully blasting the bottom of a kiln shelf with a higher temperature than a firebox would ever see, that's encouraging. I did consider double stacking 5/8th" kiln shelves to be even more robust.

It will be a white oven topped with kiln shelf. I had no reservations about putting on on top where there is less heat and no weight load.  

So far I'm hoping to stick with the cast slab precisely because it will hold more heat, but I'm open to folks here trying to convince me to go kiln shelf instead.

The slabs spent Sunday in the oven, wife barely approved. I read that the free moisture in refractory is the most dangerous and that's what requires a careful and slow ramp-up. So they spent 9 hours slowly ramping up to 500F degrees.

After that I brushed off more dry/loose material and the edges look pretty rough. But the slabs have a nice ceramic "ring" to them now that they are partially sintered.

I took them out to the shop to mock up the core. The upright bricks on top are the oven walls, which still need a kiln shelf top. More details on the core and Shorty riser will come in another post.

Now you can see why I chose refractory slabs over kiln shelves. I designed the build to support the oven above, and I'm afraid of the direct flame on just the center of the kiln shelf would cause uneven heating compared to the sides that are resting on brick. Uneven heating of tile is what makes it crack so I have the same fear with kiln shelf. I'm much less afraid of this with a 2 & 1/2 inch thick refractory slab. But still undecided if THIS slab is good enough. Next up: I'll heat the slab pieces with a powerful yard torch to see how they fare.  

An update: I opened the mold and sprayed the tops and edges with water. Then re-covered in plastic again for another 24 hrs. The top edges that got squirted from both exposed top and sides seemed to have firmed up a bit. The bottom edges were still awful soft (dry/powdery) so when I took a wire brush to all the edges, the bottom edges gave up more and exposed some aggregate. A metal scraper knocked off any loose aggregate.

No idea why those bottom edges were so dry. The soy wax I used was plenty thick and souldn't have robbed moisture. But the bottom face is nice and smooth at least.

Now they're suspended over a dehumidifier to begin the drying process. I think I'll keep playing with these and not count them as a 100% loss just yet. I will do the gradual heating ramp up curing and see how they look and feel after all that.

thomas rubino wrote:
I was warned, possibly by Fox, who has vast experience vibrating cast items, to be careful "Not" to over-vibrate!

I took the warnings not to over vibrate or over water too far!

So now I'll put these slabs through a torture test just for fun. And probably end up re-casting (a $100 mistake.)

Or I could sandwich the slab in kiln shelves. I could have used kiln shelf from the get-go but that's more expensive and I wanted the thick cast refractory slab for mass since the top of the firebox will be the bottom of a white oven.

But on the bright side, sharing failures is what helps other succeed!  

thomas rubino wrote:
I used a variable-speed saws- all with no blade. My forms were sitting on plywood with a tire bolted to it.

I very much appreciated and studied that post before I made this attempt, but I suppose I was unclear on how you used the saw to vibrate the form.
So the form was sitting on a tire which allowed the whole thing to "jiggle" more than it ever could sitting on a solid surface (my first mistake.)

How did you use the saw though? Just pressed the front of the saw against the table and pulling the trigger engaged the piston inside enough to vibrate the table?