Backyard Homebrew cast oven on wood cart

[Ronstarch]

The plan: 23" internal width barrel design, cast out of homebrew, placed onto a homemade wooden cart.

Extra challenge: I've been working on this build as a wedding present for a friend, so I have to build as much of it at my house as possible, then transport the components about 20 minutes away, and assemble in their backyard.

Current status: I cast the barrel in 3 separate pieces (1. back, 2. front with inner door, and 3. flue gallery with outer door). Separately poured a 36"x30"x4" perlcrete block. Built the stand and installed the casters. Now I need to put it all together.

I'll post my steps so far for anyone that's interested, and if you have any suggestions, let me know...there's still time!

I have a few questions about floor thickness, and mounting the oven to the cart, that I'd appreciate some guidance on

[Ronstarch]

I built forms for the back and front of the oven using plywood and melamine. I quartered up some foam pool noodles and hot glued them to the forms to create rounded internal corners. I wasnt sure whether just butting the two oven pieces together and mortaring would be strong enough for the finished oven, so for the molds, I created a overlap/underlap joint, similar to how old sewer pipes join together. This was a little tricky, I'm sure there was an easier/better way.

Overall internal dimensions of the oven will be 23" wide, 28" long, and about 16" high. It's basically a half-barrel, with an extra 4" of wall height added to the bottom.

[Ronstarch]

My homebrew mix was: 3 sand, 1 cement, 1 fireclay, 1 lime, with 2% melt extract fibers and a small amount of polypropylene burnout fibers.

I think my mix was a little too dry, but overall, I was able to build up the homebrew around my forms and press it into place. Next up was the unmolding...I unmolded the castings after 24 hours, because I didn't want shrinkage pressure to crack my castings, especially since they were cast over rigid wood forms (as opposed to sand). As you can see in the picture of the back piece, I have plenty of voids and ripples where each new "course" was laid onto the previous one. This is why I think my mix was too dry. Also, I cracked the front piece entirely in half while removing it from the mold (got too aggressive wriggling the plywood out). Since the casting was still moist, I mixed up some more homebrew, laid it on both broken pieces, and stuck them back together...and crossed my fingers

[Ronstarch]

I filled the voids in my still-moist castings using a richer mix of the homebrew (2:1:1:1). I worked the homebrew into the larger holes and voids, and then smoothed everything out with damp rags The final result looks pretty good. Also, the repair of the front piece seems to be holding rather well. After the repairs and patching, I damp cured the pieces for a week. I'm not sure if these voids and cracks will show themselves once I start firing the oven; hopefully not. The sewer-pipe connection wasn't quite perfect, I needed to take an angle grinder to the edge in order to get the parts to fit together. Next up, flue gallery.

[Ronstarch]

For the flue gallery, I was able to re-use the mold from the front of the oven, with a few modifications. I shortened it, so that the flue gallery is 7" total depth. Also, I made the outside door opening about 1" large than the inside door opening. The vent was designed to hold a large double-walled stainless steel chimney I got on craigslist. The chimney is 6" ID, 8" OD, so I used a coffee can to make the vent match up at the top. The chimney slips on, with the inner part sliding into the vent, and the outer collar sliding over the outside.

I cast the flue gallery in place over the front part of the oven, using a tarp so that it wouldn't stick. This was much much easier than trying to make the sewer-pipe connection; I wish I would have cast the front piece of the oven over the back piece in the same way.

You can see how the three oven pieces fit together in the picture (like a little caterpillar or something). Flue gallery weighs about 80 lbs, front piece 100 lbs, back piece 120 lbs.

[Ronstarch]

I constructed the cart using some reclaimed lumber, with stainless steel carriage bolts and lag screws. Built a shelf on the bottom for wood storage. Targeting a deck height of 42". The cart is 34" x44". I bought some locking 4" casters online, they roll pretty smooth for now (until they've got 500 lbs of pizza oven on them).

I'm now at the stage where I need to mount the pizza oven onto this cart. Here's where I could use some advice.

1) How to secure the perlcrete block onto the cart? It's 4" thick perlcrete (5:1) bonded to hardiebacker board. The perlcrete block is not quite flat on the bottom (or the top) so I was thinking I might need to lay down some thinset on the wood so make sure the block is evenly supported?

2) For the oven deck, I have firebrick splits (1.25" thick). Given that the oven is 1.5"-2" thick, will I be ok using these thinner firebricks for the floor, or would I be better off using full thickness bricks? Tradeoff is I'll lose height clearance on the door (the guy wants to be able to fit a turkey in the oven). Also, I already have the splits.

Thoughts?

[UtahBeehiver]

1.25" floor is a on the thin side, it does reduce your floor's ability to store heat and you will have to recharge the floor more often. But since you have the splits already your decision is made. Just be aware of the heat storage issue. There were posts recently about turkeys and oven sizes, I believe SableSprings noted that he could get a 20 lb turkey in a 12" high door, going by memory....

[Ronstarch]

Thanks Russel, appreciate the response. Anyone have thoughts on mounting the oven to the cart? My current idea is to lay down a bed of modified thinset over the wood, screw down a sheet of 1/2" Hardie board over that, then more thinset, then the perlcrete block (which is smaller than the table top). Will this work? Should I drive screws up from underneath the table, through into the perlcrete block? Should I put some type of waterproof membrane down onto the wood before doing any of the above?

[david s]

It will be gravity largely that holds the oven in place, but you should get a pretty good bond with the thinnest too. A waterproof membrane may act as a slip layer reducing any bonding so I think I'd be skipping that. Screws going into the vermicrete probably won't do much as it's such a weak material although they should ensure there is never any sideways movement.
Re the floor thickness, you could lay a .75" thick of home-brew over the vermicrete slab to increase the floor thickness and its thermal mass bringing it to the same thickness as the dome.

[UtahBeehiver]

Pouring an additional homebrew for under the splits is a great idea that David has. SInce your oven shell is homebrew was you should already have the materials on hand.

[shanxk8]

What about a physical attachment/barrier around the entire sandwich of wood/hardie board/thinset/perlcrete/oven floor? Having a fully encircled barrier that is attached to the cart might hold all the layers together & prevent sideways movement. This could be wood or metal, and under the external decorative covering or exposed.

Just my quick thought.

[Ronstarch]

I appreciate the responses. I went ahead with the thinset-hardie-thinset-perlcrete-homebrew-splits approach. The hombrew layer is about .5-.75" thick. I was able to get it pretty flat on top; should I still put down a bed of sand/clay under the firebricks? I was always afraid that the dry sand/clay particles would migrate up onto the food.

I mounted the back and front pieces of the oven into the still-soft hombrew, and mortared them together using more homebrew. Haven't attached the flue gallery yet; thinking of using perlcrete instead of homebrew to achieve more thermal isolation from the oven.

After that, I'll add 2-3" of ceramic fiber blanket, then a layer of perlcrete, then a render layer.

Question: do I insulate the outside of the flue gallery as well?

Thanks again for the responses so far, and for all of the info on this forum!

[shanxk8]

Not an expert here, but I put one layer (1") of CF blanket insulation on our flu gallery (vs 5" on the dome). It has a thermal break with fiberglass rope between flu and dome.

I did this as the outside of the flu got fairly warm from the hot smoke and whatnot during cooking fires. I figured a little insulation between got bricks and stucco makes sense.

[Ronstarch]

Hey all, I finished this oven last October but never posted any pics, so thought I would post a few as well as some lessons learned. Overall, the oven works well and looks pretty good (if I say so myself). For insulating the oven, I used a ceramic fiber blanket (2 layers of 1" each), metal mesh, perlcrete over that (about 1"), and then 2 layers of render. I did a brick arch entrance and a little landing in front of the oven mouth, both using some brick-colored patio pavers I found lying around. Drying fires for a week before bringing it up to temp. For the chimney, I have a removable stainless steel chimney from craigslist (6" ID) that draws well.

The two biggest issues with the oven: uneven heating due to barrel shape (cold spots in the corners), and because the barrel is a little "taller" than a true semicircle, the bottom sides of the oven also take a little longer to heat up. The other issue is that, as predicted, it's difficult to roll the oven on the 4" casters due to weight.

Thanks again to all who posted on this thread and helped me out with ideas!

[Ronstarch]

And a couple more photos. Takeaway: having now built and used both, I strongly prefer the dome shape vs barrel shape. Homebrew seems to work fine for a construction material. The wire mesh was very annoying to work with, but made a good substrate to render the perclrete against. The wooden cart is strong enough and sturdy, but 4" casters aren't enough to easily be able to roll the oven around a concrete patio.