32" Homebrew Cast, Metal Stand - Dallas, TX

[loganc10]

Hi there,finally able to kick off my 32" build after initial research/planning last year. An overview/plan for each of the categories below, but I will add/link a dedicated question list /progress post as I get to each milestone.

Big shout out to Mullster , sergetania , Nick J C for their great build logs last year, and david s for the continued contribution; a quick read through those threads definitely fill in many gaps for the novice/inexperienced builder.

Design Plans:
Overview:

The oven will be 32", homebrew cast on a metal stand.

Parameter	Value
Dome ID	32"
Dome Thickness	2"
Blanket Thickness	2" (maybe 2x 1.5" layers)
VCrete Thickness	1.5"
Render	0.75"
CalSil Thickness	4"

Foundation:

The oven will sit on top of an old hot tub pad that is embedded into the patio.

Stand/Base/Hearth: (post #3) - In Progress

Metal stand: I bought and retrofit a 60"x60" metal table/stand off Craigslist constructed from 2" steel tube.

Platform: 1.5" Exterior plywood + thin set + 1/4" cement board, 1.5" plywood edges sealed with Titebond 3 waterproof glue
Waterproofing membrane (undecided): Potentially seal cement board with Redguard membrane to prevent moisture absorption into plywood, worth the $50?
Under-Hearth Concrete Pad (undecided): At the moment, I plan to pour a 2" pad that will go under the insulation in the shape of the oven (out to the blanket layer). My thought is this gets it plenty off the top of base and limits any water getting in the CalSil, it also raises the height of the oven floor.
Ceramic Tiles: 1/4" ceramic tile (6"x6") that will go under the insulation.
Weep holes: 4-5 0.5" holes drilled through plywood, cement board, concrete pad

Insulation:

Thermo-1200 in 2" (9 pcs for a total of 27 sq ft) for ~$130
Use 4" (2 layers) under fire brick

Firebrick:

Standard firebrick from brick yard (regular/medium duty fireplace brick?)

Dome/gallery mold:

Dome mold: Stack 12"x12"x1" foam sheets as filler, then top off with sand for shaping
Gallery mold: Design gallery in CAD, create 1" and 0.5" cross sectional slices to be laser cut out of EPS foam

Dome/gallery:

Homebrew:

Clay: Hawthorne-35 - 100 lbs
Cement, Sand, Lime: TBD

Melt extract fibers/SS needles:

5 pounds (slightly under 2% by vol)

Polypropylene burnout fibers:

Nycon Procon M 19mm/ 0.75" fibers (38 microns / melt point 320 deg F)
Purchased 2 pound sample for $10+shipping from Nycon

Chimney:

Already purchased a 6" Supervent anchor plate. I'll trim/cut some of the stock plate down so it can fit on top of the cast gallery where I'll embed in some threaded rod/bolt to attach to.

Breather valve/pipe:

Will likely do similar pipe+cap seen in other recent build

Cast Facade:

Cast tile/decorative glass front facade similar to other recent builds

Additional post to follow with details/questions of each phase of build.

[sergetania]

Looks like a well-thought out plan!

Ceramic tiles under the insulation? Hmm,interesting...

When you are making the gallery, I would suggest to make sure that you have a cavity that collects smoke into the chimney that's as wide as the gallery itself. That's one change I would like to make to my oven. I have got quite a lot of smoke escaping from the front. A full-width cavity could've helped some of the smoke go into the chimney.

Best of luck! Both building and then cooking in the oven is lots of fun!

[loganc10]

Need some advice/thoughts before I move on from the stand/base/hearth part of the build.

You will see in the attached pictures the stand and the plywood + thinset + cement board sandwich. The 2 sheets of ACX exterior grade plywood were laminated together, then 1/4" cement board was adhered using thinset/mortar and screws. Once the oven is built on cement board, the remaining exposed cement board will be tiled/cladded.

I have the following questions:

1. I'm somewhat worried about the longevity of the plywood/cement board with moisture/heat. It is sealed on the edges with Titebond III waterproof wood glue. I've bought tub of Redgaurd membrane that I was planning on applying to the cement board. Wanted to hear from others if this is a worthwhile step, or if I plan to tile over cement board should that be enough?
2. Oven will be built right on top of the cement board. I'm weighing two options right now:
   • Place ceramic tile on cement board, then 4" of insulation
   • Pouring a 2" concrete pad that the tile/insulation will be placed on top of, the benefit of this would be that it eliminates some potential for water penetrating insulation since its up off the base cement board and also raises the overall height of the oven fire brick floor (which might be uncomfortably low with current height of base)

[david s]

Two things that worry me about your build are, firstly the plywood base which although is exterior will not stand up to weather. You don’t say if your oven will be out in the weather or if it will be undercover, but either way both heat and moisture tend to deteriorate any plywood and in combination will accelerate this process. Also if you drill through the plywood to create weep holes the exposed edges of the holes are going to be places where moisture will be expelled so expect deterioration there. Can you seal the edges of the holes?

The second concern is the height of your floor. Generally it is recommended to design the oven floor height at elbow or belly button height for optimal cooking workability.
Itherwise it looks like you’ve thought things through well and done the necessary research.

Also embedding threaded rod (don't use anything other than stainless) into refractory introduces the problem of different thermal conductivity of the two materials. The steel will get way hotter than the refractory that surrounds it and over time may cause cracking where it is embedded. This is the reason stainless needles are used as refractory reinforcing because their lower mass and greater surface area are able to dissipate their heat to the refractory that surrounds them more easily than a thicker steel bar.

[loganc10]

Thanks for your thoughts. Both concerns were something that I was trying to brainstorm the best ways of mitigating. I've committed to the plywood at this point, but do regret not going with a 2" concrete pour in place of the ply + cement board direction. I chose the plywood route as the concrete would have been much heavier, and was trying to reduce total weight on the stand.

I briefly mentioned some plans to help solve/attempt to mitigate both issues in the original and following post; below is a little more details on what I have in mind.

firstly the plywood base which although is exterior will not stand up to weather. You don’t say if your oven will be out in the weather or if it will be undercover, but either way both heat and moisture tend to deteriorate any plywood and in combination will accelerate this process. Also if you drill through the plywood to create weep holes the exposed edges of the holes are going to be places where moisture will be expelled so expect deterioration there. Can you seal the edges of the holes?

I plan to seal up the plywood edges and weep hole edges with a combination of a thick water proof glue layer and/or Redguard Waterproof membrane (commonly used between the cement board and tiles in shower applications). Areas immediately on or around a plywood edge will be sealed with the glue, then the cement board top will be sealed with the membrane. Finally, along the edge of the outer ring will also be caulked. At the moment, I'm thinking I'll leave the bottom unsealed incase any moisture does find its way in, it wont be trapped. There is several inches of outer ring overhang beneath the plywood that should keep the underside mostly dry.

We just had a large pergola built, I eventually plan on covering it with Polycarbonate and putting the oven under there and vent going through.

[?] With 4" CalSil and 2" concrete separating the cooking floor and top of base, what kind of temperatures could I expect the cement board to reach? High enough to question the integrity of the membrane (shower floor tile could theoretically get 100+ deg F, though not sure how much higher this Redguard stuff is rated/useful for)?

The second concern is the height of your floor. Generally it is recommended to design the oven floor height at elbow or belly button height for optimal cooking workability.

The current stand with its original casters is only 30" high. I plan to increase the length of the legs by slotting 18" long 2" receiver tubes up the original 2" legs, then adding end cap leveling mounts. This extension, along with the 2" concrete oven extrusion on top of the stand should get the oven deck height in the vicinity of 45", which is a couple inches higher than my elbow/belly button height.

Also embedding threaded rod (don't use anything other than stainless) into refractory introduces the problem of different thermal conductivity of the two materials. The steel will get way hotter than the refractory that surrounds it and over time may cause cracking where it is embedded. This is the reason stainless needles are used as refractory reinforcing because their lower mass and greater surface area are able to dissipate their heat to the refractory that surrounds them more easily than a thicker steel bar.

Just to ensure we are on the same page, are you referring to the anchor plate mounting or using steel rods for refractory reinforcement? I was only referring to embedding in an anchor point for the plate, similar to what was done by sergetania here.

---

All-in-all, a understand there is compromises with the plywood approach, and it won't hold up the test of time as well as a masonry based stand; however in the 5 year range there is a fair bit of uncertainty when it comes to still being in the same city/house. So my target for it withholding the wear and deterioration is something closer to the 5 year mark.

Thanks!

[david s]

"Just to ensure we are on the same page, are you referring to the anchor plate mounting or using steel rods for refractory reinforcement? I was only referring to embedding in an anchor point for the plate, similar to what was done by sergetania"

Although the top of the flue gallery won't see temperatures as high as the dome or floor, the same principle applies. You may get away with no problems there, particularly if you keep the diameter down to reduce the volume. I'd suggest nothing thicker than 1/4", but anything other than stainless is likely to corrode in that position.

Regarding the extension of the legs on the stand, as the oven will be heavier than you think, some welded diagonals on the legs would be advisable.

[loganc10]

After a long hiatus as life got in the way, the last couple months I have made a bit of progress in completing this project, but still a bit to go.

Admittedly, I got somewhat in a "oh well if its wrong, as long as its built" mindset. As an engineer and inexperienced builder, I was splitting hairs way to much on the design and execution; and finally one week/weekend I decided to quit over-thinking a just build as much as I could without stopping and asking too many questions.

I can't edit the original post due to its age, so I'll update below and link to subsequent posts outlining what has been complete so far and current questions going forward.

Post #1 still captures the over-all goal and most design choices accurately.

Overview: (post #1)
Stand/Base/Hearth: (post #5, post TBD) - Done
Weep Holes & Tile: (post #8) - Done
CalSil Insulation: (post #9) - Done
Firebrick: (post #10) - Done
Dome/gallery mold: (post #11) - In Progress

[loganc10]

Concrete Pad/Hearth, Weep Holes, & Tile
As described in post #5, I have 1.5" of exterior plywood, thinset, 0.25" cement board, and waterproof membrane (Redgaurd).

I pre-drilled 5 weep holes and sealed the hole edges with the membrane.

The 2" concrete pad was poured, using foam pieces for weep hole location.

I probably could've been a bit more strategic with the tile by breaking it into smaller pieces or making clear channels to the holes. Instead, I just figured that water will find its way of least resistance; and placed the tile in a neat grid. Since the insulation/tile level will be 2" up off the base layer, I thought it was less of an issue.

[loganc10]

CalSil Insulation

I used two layers of Thermo-1200 2" CalSil insulation, making sure each layer was oriented 90 degrees from the other.

[loganc10]

Firebrick, Thermal Break, & Water Membrane

I found low-duty Whitacre Greer firebrick at a local mason supplier. I wasn't super happy with the condition of the bricks, there seemed to be a bit of thickness variance and some of the bricks had some pits or cracking; which I tried to pick around / cut out. Hopefully they will be suitable, and I'm just being overly anal.

I added a 45 degree cut-out/thermal break to the gallery bricks, then slid a left over piece of CalSil with the same angle into the void. Pretty happy with the result.

As shown in the pictures, I added some additional Redguard to the concrete pad and first layer of CalSil, I also put it under the gallery landing bricks; as documented by another user who reported it held up pretty well after a few years of use.

[loganc10]

Dome/Gallery Mold & Planning

Post #8 - #10 came as quick progress over the course of 3-4 days, though now I'm at a bit of a cross-roads and be procrastinating on the casting of the oven.

I laser-cut and will laminate pieces of 0.5" and 1" foam to create the gallery mold, then will create a sandcastle for the dome (with some styrofoam cooler/blocks to reduce amount of sand needed).

As I am dry-fitting the gallery mold, I'm concerned that it might be a bit longer than ideal. The wider section of the gallery (not including lip section) is currently 12" (30cm) long. I also plan on having a 2" thick cast facade on front as well, further increasing the depth.

So with that, I need to make the decision to trek on as is, or cut back the brick, insulation, and concrete pad 2-3 inches. I'd really prefer not to, but would like to get other's input on their lengths and if this would be a major or minor hinderance when working the oven. For what it's worth, I am taller at 6'2"/6'3"; so longer arms might help.

[AndreasP]

How wide and tall is your opening? I think that the width makes a big difference as far as access is concerned.

I ended up making my dome opening 19" wide and 10" tall in the center, 8" on the side. 19" is on the wider side. Post#42 in my build thread has a comparison table if what I could find.

My entrance is really shallow, 8" .
I still need to add a 2" fascia that i have cast.

We have done pizza several times now and everything worked really well. Good access and with an insulated door l the oven is still at a out 500F the next morning.

Not sure if I would redo your base, then again, it wouldn't be that much work. I am sure others with a deeper gallery will chime in with their experience.

[loganc10]

AndreasP, good point. My oven will also be 19" wide and ~10" tall.

Including my 2" front face, I'll have a total of 14" for the landing/gallery. Searching around a bit more, it doesn't seem terribly uncommon to see 12-14" lengths around the forum, especially on the brick oven side of things.

I'll think about it a bit more and see if anyone else chimes in. I'm leaning towards no. While it would be pretty simple to cut the brick and insulation back the few inches, the concrete pad on the bottom would be more annoying/difficult needing to use an angle grinder.

[loganc10]

Dome mould
I decided to cast in two separate parts - dome and gallery. Dome mould was made using lid of styrofoam cooler, some additional foam sheets, and sand with a little clay mixed it. I built a jig for the hemisphere, but it probably wasn't needed, patting with a trowel did a decent job at shaping and the jig was mostly for a radius spot-checking.

[loganc10]

Dome Cast

I cut long triangle strips of light kraft paper and soaked in flour/water mixture. It was very windy putting the strips on, so needed to rig some tarps up to block the wind. Eventually with another set of hands, we were able to get everything laid on the dome then kept spraying with water to keep wet/damp.

Mixed homebrew in 5-6 gallon batches, taking around 4 total batches.

Covered in two layers of old damp bath towels and sealed with liberal amount of plastic wrap and tarp.