Scratch build thread - 36-inch inner diameter dome oven

[mnagy]

Here’s my dome build. Next I’ll insulate with fiber blanket and render over it. Still haven’t decided on render mix. And I’m terrified about drilling a few screws into the dome base to hold down the chicken wire. We’ll see how it goes.

https://www.tiktok.com/t/ZT8MWXyE2/

[david s]

I know that covering the blanket in chickenwire is the general method used and recommended by most builders, but here are 4 good reasons why it’s a poor solution and why I have never used that method in any of the many ovens I have built.

Drilling into the brick is asking for a crack to occur at that point, particularly when filling the hole with a steel screw, that will want to expand faster when heated, than the less conductive brick that surrounds it. I have always thought adding highly conductive steel wire to an insulating layer is counterproductive. Additionally if the blanket layers are compressed by the chicken wire it will also reduce the insulation capacity of the blanket. Finally, it is an arduous and time consuming task to apply chicken wire over a compound curve.

A layer of lean vermicrete over the blanket will easily restore a nice form as well as provide a nice firm substrate to render on to, at the same time as providing additional insulation (a 10:1 vermicrete has about the same insulation value a ceramic fibre blanket).

It’s obviously not possible for you now, but some thin wire ties embedded into the brick joints at several places is better than drilling.

A nice video of your build by the way, thanks for sharing

[mnagy]

Thanks for the thoughts! What if I drill a few 3/8” holes and just “glue” some kind of fastener in there with mortar? That way I’m not screwing into it.

mare you also suggesting that I don’t actually need to tie down the blanket? That maybe the vermicrete would hold it down? Or are you saying that I might want to insulate with vermicrete only instead of the blanket?

I’ve got time to do this right.

[david s]

Drilling a large diameter hole increases the risk and you'd need a "glue" that will withstand high heat, but it could work. Can you fix into the underfloor insulation layer?
As I said before I have never used chicken wire to tie down the blanket. In fact I don't tie the blanket down with anything. As an extreme example, here are some pics of a large (1.6m internal) oven I built which shows the vermicrete over the blanket. Unfortunately the owner installed the stand and cast slab really close to the walls on either side of the corner (I hate corner builds). This meant that there was only room for two layers of 1" blanket on the sides, so i compensated by putting 5 layers on top. The 35mm of vermicrete over the whole oven easily covered the dome to restore a nice shape. It required a variation in vermicrete thickness to smooth out the steps created by the uneven blanket layers. The vermicrete application was difficult at the sides and the back. The only way I could access the back corner was to continually crawl under the stand and squeeze into the triangle in the very corner,( a real bitch)

I would not recommend insulating an oven with vermicrete only because a thick layer takes ages to dry. The beauty of the blanket is that it's already dry. A 1.5" or so layer is pretty dry after a week, especially if out in the sun and wind. We set up a fan because this was indoors.

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[mnagy]

This is great, thanks David. I’ll go ahead and use the fire blanket without the chicken wire. I feel like the dome is rough enough that the blanket will sort of stick to it like velcro. Then I’ll just render right over it. Just put the flue gallery on tonight. Really excited to start the curing process in about a week or so!

[mnagy]

What do you think about using small pieces of duct tape to hold the ceramic fiber blanket together a bit at the seams? I realize the render won’t stick to the tape, but I wont use a lot of it, and the render can just float right over it.

[mnagy]

Entry arch and chimney mount.
https://www.tiktok.com/t/ZT8M33rKP/

[david s]

What do you think about using small pieces of duct tape to hold the ceramic fiber blanket together a bit at the seams? I realize the render won’t stick to the tape, but I wont use a lot of it, and the render can just float right over it.

I think you will find it's unnecessary. Tape does not stick to blanket well either.
I fill any gaps in the blanket with cut pieces of more blanket. It is a dream to cut and fit, but as. 10:1 vermicrete is about the same insulation value any holes can be filled with the mix also. I think you are over- worrying.

[mnagy]

Thanks David!

[UtahBeehiver]

You can use small TapCons to drill into the base to fasten wire to hold the blanket down. You don't need many. This is what I did to fasten my wire down.

[mnagy]

Thanks! I like this approach. Good compromise. I’ll just put 6 or 8 screws in the counter top and wrap them over the dome. I’m not going to use fiber blanket on the entry tunnel (I’ll just render that) because I have a gap between that tunnel and the inner arch which is filled with heat stop caulking.

I’m going to give the dome about a week to cure, and then I’ll start slowly drying it out with small fires. Looks like I’ll be just in time for winter.

[mnagy]

Here’s how I wound up doing the fiber blanket. Similar to UtahBeehiver. Thanks all!

https://www.tiktok.com/t/ZT8Mo5qod/

[UtahBeehiver]

You can start curing with charcoal briquettes, gets you about 200 F without flame impingement and you can do a dutch oven or cast oven meal on the coals as a bonus. When you start wood, very slow go. One extra piece of wood will spike the temp very easily. This is where we see many builder get impatient going too fast too hot and crack their ovens. The turtle wins the race in curing an oven. Also, any thoughts of installing a vent at the apex of the dome since you sealed the bottom in with AL gutter foil it will also keep water that gets in from getting out. By install a vent in the apex, water vapor can escape. When water sublimates from a liquid to vapor the volume increases by 1500 X with the potential of pressurizing the dome and possible cracking. Vents are cheap and available at any auto store for under 10 bucks. Both Gulf and I use them in our builds. We used a threaded pvc bushing embedded in the stucco with the opening to the depth of the blanket.

[mnagy]

Man. Thank goodness for you guys. I do have drain holes in the stand, with tile/channels under the vermicrete layer. Can the water escape downward? If I get a vent on top, you’re saying it only needs to get to the blanket layer? Thank you again for following along and pointing out these things!

[mnagy]

How about something like this?