Pdx 42" update

[mongota]

My challege is that I'm nearly to the edge of my hearth in the back, I have about 1.5" available now for both the vermicrete and stucco. Can I skip the vermicrete and go directly to stucco, or perhaps thin down the vermicrete layer? Or would I be better off adding an extra 1" of blanket around the entire oven and then going straight to stucco?

With those choices and those dimensional restrictions, I'd do a third layer of 1" blanket. Then stucco lath (expanded damond mesh). Then stucco.

When I built my oven I thought the lath would be a pain in the rear to apply but it was ridiculously easy and surprisingly fast. It made the subsequent stucco application worry free regarding my concerns over compressing the blanket while troweling on. I worried that I might compress the insulation while troweling it on, and the insulation expanding/rebounding and possibly cracking the stucco while the stucco layer was still plastic, before it had cured/hardened.

Congrats on your progress.

[Macrinehart]

Gulf - well noted on your advice. I do have a plan for a steam vent in vermicrete/stucco at the top of the dome. I've purchased a marine grade stainless steel mushroom cap which should provide sufficicient ventilation without letting anything in.

As for the transition piece, I had not planned to use any hardware for anchoring, although that is feasible. My thought was to use this fiberglass tadpole gasket (picture attached) with 2000F rated adhesive. This example features a 3/4" bulb diameter. I intended to glue the tail piece to the bricks and securing the bulb piece to the inside of the SS material ould provide both flexibility and a good seal. I suppose I could also provide some spacer material around the transition piece and use someting like this fiberglass gasket to seal that gap too.

Incidentally, I am working with a local fireplace guy on the transition piece. This guy has in business since the 70s and has accumulated a lot of vintage stove material over the years. He proposed salvaging a cast iron transition piece that integrates with a vintage stove model he has from his stock, but only if it fits.

I am a little skeptical about this idea. For one thing, cast iron is heavy, and I'm not sure if I want all that weight resting on the opening arch. Secondly, I don't know what that would do with respect to movement of the dome. Instead of being able to slide, I'd be afraid that lateral pressure would transfer through the cast iron and onto the opening arch.

Any thoughts? Am I good to be skeptical on this or is cast iron a good idea if the size works?

Thanks!

[Gulf]

I think that you have all of it covered as for expansion of the actual dome.The CFB is doing that. However, you need to make a place for the steam to escape during curing if you haven't included that in your design. Also, there will need to be something that will performs as an expansion joint between any ss steel and any masonry including the vermicrete. As for actual attachment to the chimney, I would like to see the "transition piece that you are using. Usually, it is just a heat resistant gasket that is homemade. Where ss bolts are used for the actual anchoring, oversized holes through the ss a good practice to allow for expansion.

[david s]

The expansion at our service temperatures amounts to about 3-4 mm every time you reach pizza temperature.

[Macrinehart]

Thank you Gulf and david s for the advice.

There is one more area I have questions on before going too much further. This pertains to accounting for material movement during heating and cooling, particularly where different materials are interacting around the base of the chimney.

Elsewhere I've read that the oven dome may move during heating and cooling. I assume that the insulation layer helps to allow this movement without cracking the vericrete or stucco layers of the dome.

I have also allowed about 1/2" gap between the dome and opening arch which will be sealed with fiberglass stove gasket material. It's pretty tight but should allow for some minor flexibility.

Over the interior and exterior arch I will have a Stainless steel transition to the chimney, and because this connects to both the interior and exterior arches, I have my doubts about the best way to attach this piece. I'm thinking of using fiberglass tadpole tape, as I think it should help provide a good seal with some flexibility to isolate interior dome movement from the exterior arch and the vermicrete and stucco layers.

Finally, I intend to surround the base of the ss chimney transition with vermicrete and stucco in the back the insulation till butt up to the ss transition piece. My plan is to leave only the front face of the exterior arch exposed.

I am a little concered that as these different components heat and cool and interact I could start having issues.

Can anyone see any yellow or red flags?

Thank you!

[david s]

You could try applying a stucco/render coat directly onto the blanket, but it is a very poor substrate to work to. A vermicrete layer as well as providing additional insulation, sets up firm and covers bumps in the blanket, particularly if the top of the oven has an extra layer which creates a step (as in post #261)

[Gulf]

Looking back, you have a rectangular hearth slab. Your oven is round. If I am correct, you will only be hanging over just a few inches for about a foot at the apexes of the sides and maybe the rear of the dome. That's not too much. Just lay down a piece of hardy board at those points to cantilever over those short spances. Reinforcement mesh in the first coat of stucco would be good to reinforce those areas.That's not just an opinion. I have done it lol.

[Macrinehart]

Hey builders - I have a question on the use of vermicrete for the dome. I have 2" of ceramic blanket insulation around the entire oven and will layer an extra 1" blanket on top, which I understand will be the hottest area.

I read on another post that with 3" of blanket insulation the vermicrete layer could be skipped. My challege is that I'm nearly to the edge of my hearth in the back, I have about 1.5" available now for both the vermicrete and stucco.

Any thoughts on this situation? Can I skip the vermicrete and go directly to stucco, or perhaps thin down the vermicrete layer? Or would I be better off adding an extra 1" of blanket around the entire oven and then going straight to stucco?

Many thanks!

[Macrinehart]

Memorial day weekend ends with my project feeling much closer to completion. I got started with insulation today. I came up a little short on material so it's back to the ordering more. I'm also hiring out a custom SS chimney transition, and there is chimney pipe to buy plus a cap. Chimney pipe is really expensive!

I was also looking for a vapor vent for the top of the dome. I know there are some less expesive options, but I found a vendor that manufactures marine grade stainless steel mushroom vents. It looks really nice, so I decided to get one. I connected with the owner and he will make one without the powder coat that the typically apply to avoid and risk of noxious odor at high temps.

I keep beaking parts of the opening arch. Yesterday I cracked one of the joints when I was getting in the oven to inspect my work. Then today I broke the joint on one of the bricks that was to be the base for chimney. I had to mix more mortar to fix that, as I used the last batch yesterday. And then while I was positioning it again the brick broke! no worries, no one will ever see it. I decided my oven needs a break from me, so waiting for the next batch of materials is a good thing.

[david s]

Insulation values are the reciprocal or opposite of thermal conductivity values, so the higher the thermal conductivity,the lower the insulation value. Thick conductive materials store a lot of heat very quickly.

[Macrinehart]

david s - I'm not sure I understand the problem, besides weight. Does the higher thermoconductivity effec the oven performance? What effect does it have?

2mm seems very thin.

In other news, I closed the dome today! COULD I BE DONE WITH THIS STAGE? To be honest, I have doubts. The after the 11th course the remaining opening was too big for a 1 piect plug and too small to allow more that one more course. So I custom cut 4 pieces to plug the top.

There was a lot of trimming to get a good fit, and in the end my plug is a little uneven. But is seeled! I got inside the oven to check things out and noticed its a little uneven plus there was a pretty deep gap inside. I filled the gap with mortar.

Attach photos. Let me know if I need to have a redo.

[david s]

Steel has comparatively high thermal conductivity which will both heat and cool rapidly. At 1/2” thick you will have a lot of thermal mass there, effectively sapping the oven of heat as well as making the door very heavy and hot to handle. To overcome warping issues at baking and roasting temperatures, which can create sealing problems, mild steel needs to be relatively thick (approximately 2mm), but any thicker starts to introduce the other mentioned problems.

[Macrinehart]

Made good progress on the oven today, and I'm confident I'll be closing the dome this weekend! FINALLY! haha

Today I rebuilt the opening arch. I'm custom cutting the bricks to provide a level, rectangular opening for the smoke box, which will transition to 8" stainless steel chimney. I finished front of that opening today, the back will come tomorrow.

Last night our blacksmith friend Arnon came over and inspected the progress. He'll be building my door, for which he plans to cut a 1/2" think sheet of steel to size. The door will have a slide damper, basket handles and coiled feet to for support. In addition he's forging a long-handled peal and coal rake.

[Macrinehart]

Here is the outer arch with my form removed. Some of the lower bricks were tilted incorrectly, which I fixed as I was approaching the top of the arch. But looking at it now I'm thinking about taking it appart and redoing things between bricks 4 and 14.

Update: I was showing off the oven to my dad and he used the opening arch as a handhold and accidentally pulled it apart. So I guess that settles the matter; I'm rebuilding the opening arch.

[Macrinehart]

Hi David - well noted, and I have the rebate per your guidance, my outer arch bricks are cut lengthwise so the outer arch has less depth than the inner arch to create the reveal.