Idaho 36" Build

[AJH]

It looks like I'm going to want to put the oven in the middle of the pad, which will make the chimney line up with the ridge beam on the shade structure. I'm thinking that I could elbow it far enough away with a couple 45 degree double walled chimney elbows but worry that the heat will be too much on the first elbow. Anyone do something similar? My other option was to use brick to angle it over far enough to run a straight chimney pipe through the roof panels far enough away from the ridge beam.

[UtahBeehiver]

I think UL Standard 103 does not allow insulated ells greater than 30 degrees. But you can get around this by using 15 and 30 degree ells, see attached. This is from the Selkirk catalog.

[AJH]

Well, I picked up a 10 inch Chicago Electric wet tile saw 2nd hand and picked up the blocks I need to make the foundation. Looks like I may be cutting some pavers this weekend to level the bottom row and then dry stacking the blocks. I'm going with a 3.5 block by 4 block configuration, it's a little smaller than what's in the plans, but it looks like I'll have enough room to make the dome and insulate it with 3 or 4 layers of blanket. I haven't decided on a final render coat or framing it with hardie backer...

[rsandler]

Nice find on the saw--I built my first oven using that model, and it worked great. Sold it after finishing the facade and got like 3/4 what I paid for it, and I bought it basically new (more precisely, new-in-box from a guy on craigslist at a modest discount from retail).

On the block stand, I might suggest going a bit bigger. I built my first oven stand too narrow to have much room for error with respect to the finish, and regretted it. You may have already worked out this math, but with CMU's actually sized at 15.625 inches, 3.5 blocks gets you about 54" width all told; 45 of that is oven (36" diameter + 2 walls 4.5" thick), another 6 minimum is insulation (3 per side), leaving you just 3 inches (1.5 per side) for finish. And that's assuming you have the insulation wrapped tightly on the sides which I failed to do. You'd definitely need to do a render coat in that case--no room for tracks, and probably no reveal either, even with render. A few more blocks and bags of concrete don't cost much, but they'll give you more flexibility to change your mind when you get done with the dome. Don't know about your foundation space though.

[UtahBeehiver]

One suggestion on the wet saw. Take the water pump, extend the plastic supply hose, and place the pump in a homer bucket that you refresh with clean water as needed. This keeps the pump from sucking up all the cutting sludge thus extending the pump life. Cheap fix, few bucks for a piece of hose.

[Gulf]

+1 on keeping a clean water feed to the sawblade. However, the bucket will go dry when your mind is on other things. I have used a couple of hacks over the years for an auto-refill. Check this link out to a quick, cheap, and easy solution.

[AJH]

On the block stand, I might suggest going a bit bigger. I built my first oven stand too narrow to have much room for error with respect to the finish, and regretted it. You may have already worked out this math, but with CMU's actually sized at 15.625 inches, 3.5 blocks gets you about 54" width all told; 45 of that is oven (36" diameter + 2 walls 4.5" thick), another 6 minimum is insulation (3 per side), leaving you just 3 inches (1.5 per side) for finish. And that's assuming you have the insulation wrapped tightly on the sides which I failed to do. You'd definitely need to do a render coat in that case--no room for tracks, and probably no reveal either, even with render. A few more blocks and bags of concrete don't cost much, but they'll give you more flexibility to change your mind when you get done with the dome. Don't know about your foundation space though.

I've gone through so many different stands now in lots of different locations. The foundation is 12' x 24' and I have a Gazebo with posts 11' apart. After some more deliberation, I've gone back to the original corner layout =) Unfortunately, that means I'm short a few blocks from what I picked up the other day. Not a big deal though since I need to cut a bunch of pavers to fix the slope in the foundation. It slopes down about 2.25 inches over a 6' span. I am also going to drill a hole into each corner to anchor the rebar in the foundation. 4 should be enough, the rest of the rebar can just sit on top of the foundation.

[AJH]

Two new questions for the masses:

1) How much extra time for heat up is needed if I lay the floor bricks on their sides and have a 4.5 inch thick floor instead of a 2.5 inch thick floor? I'm still debating if I want the extra thermal mass for cooking bread the next day, but I don't think that I'm going to be making dozens of loafs... probably a handful at most, so the 2.5 would probably be plenty... is it easier or harder to cook pizzas on a thicker floor? I can see it not needing time to recharge between pizzas, but also see wiping it with a damp rag not cooling it down enough to cook on either.

2) Where is the best place to make up the extra height that I want for the floor? I can lay extra on the block stand to get me where I want to be, or I can put a layer of clay/cement brick under the cal-sil board to make up the difference.

[Giovanni Rossi]

AJH, I can't answer your questions directly bc I don't have anything to compare. But, here's some info to help decide. My 42" floor is 3" of refractory sitting on 2" of CaSil and 2" of FOAMGLAS. My dome has 4" ceramic fiber blanket and 2" pericrete insulation. I start baking pizza about 75-90 minutes after starting my fire. I don't have an insulated door and can bake bread for at least 12 hours starting the next morning.

Also, I think it was SableSprings who cautioned another builder on using clay/concrete brick directly under the CaSil bc of moisture wicking.

[SableSprings]

AJ, I think just laying the firebricks flat (2.5" cooking floor depth) is plenty for residual baking. My oven's a 39" diameter slightly modified dome (beavertail) with 4.5" (half-brick thickness). I normally load a cold oven up at 10-11 pm and fire it up. I dampen the fire down with my insulated door once it's going so that I'm looking at 700°F mid-morning the next day with a few coals still glowing. I clean ashes/coals out and close up the oven with my insulated door to make sure the bricks are equalized temps throughout. I normally shoot for baking about 2-3 in the afternoon and find I can do easily 12-16 baguettes @ 550-575°F (loading 6-8 baguettes in for a bake of 15 minutes). Oven has usually cooled down below 500 after those 2 bake loads, so I open the door a bit and plan on doing 5-8 whole wheat rounds when the temp drops closer to 475 or so. Too much insulation or brick thickness would make this cooking range more difficult. I just have about 4" of perlcrete (5:1) for my floor insulation.

The problem with a thicker floor is that is takes significantly more wood (and time) to bring it up to cooking temps. The Alan Scott design uses the much thicker floor and "doghouse" style because he was looking at cooking more than a couple dozen loaves every day with just a little temp refresh during the evening...and his design really isn't made for pizza...tough to get that much brick mass up to pizza temps.

As far as your getting to the correct height of your cooking floor, as John (Giovanni) noted, clay and/or concrete will wick moisture up into the floor of your oven's insulation. That's why tiles, weep holes, FoamGlas, specifically designed moisture resistant ceramic board, etc. are highly recommended...insulation only works well when it's dry. I'm glad you went with the covered area as that definitely cuts down on the water on & around your WFO. Figure out your preferred oven floor height, subtract brick thickness, insulation thickness, moisture break (tiles) thickness from that and pad your block stand hearth to that height using pavers or other masonry (preferred) products.

Hope that all makes sense...looking forward to your build! Don't forget you are going to need more wood storage than what will be possible under the oven and lots of prep/serving space near the oven.

[rsandler]

From your description of how much bread you want to make, 4.5" of floor mass is probably overkill. My 36" oven in DC had the normal 2.5" floor, 4" Calsil underneath and 3-4" CF blanket on top. It could be hot enough to start cooking pizzas in under an hour, but would be in better shape for baking bread the next day with a 75-90 min fire (or better yet, a few more logs on the fire after the pizza cook was done). The two things to keep in mind are

(1) even a 36" oven like you're planning can bake 8 loaves at a time. Indeed, you'll get better results from a full load, since the steam coming off the dough helps with baking. If you aren't planning on dozens of loaves at a time, you're looking at 1 or maybe two batches. 2.5" floor is plenty for that.
(2) If you aren't retaining enough heat for the amount of bread you want, it's easy enough to toss a couple logs on the hot coals the morning after a pizza bake to get back to bread baking heat. 20 minutes of live fire was usually plenty for me, even when the oven wasn't very well charged and was under 400F the next day.

[david s]

It depends on the clay composition of the tiles as well as the degree of their vitrification which governs how porous they are. Generally the higher fired they are the more vitrified they become, like the difference between porous earthenware and non=porous stoneware. The concrete supporting slab itself can also be made with reduced porosity by including an additive in the mix as well as sealing its top surface to reduce wicking.

[AJH]

I had a productive Saturday. I cut all the bottom bricks to get everything level and then stacked up the base. Next up is drilling some holes in the pad to embed a few pieces of rebar and then getting all the framing and reinforcement done.

[AJH]

Well, I finally made some more progress on the build. I got the supports put in, with shims. I laid out some 2x6's on the supports to pour the concrete table on. I got the rebar cut and bent and laid out the grid. And today, I wired all the rebar together nice and tight. Concrete table top will be about 4.5 inches thick... I'll probably hate myself before the end of the concrete pour after lifting so many bags of concrete, but oh well... I also got my cement mixer put together over the weekend. So, now I just need to put some silicone caulk in the corners and start mixing!!

[UtahBeehiver]

Install a few 1/2" PVC sleeves with the top covered with tape and just below the screeding surface. These will be for weep holes. When the pour is cured you can tap through the sleeves from the bottom and you have your weep holes. Or you can mark you rebar locations and drill through later. Either way, silicon a piece of window screen of the bottom hole to keep the bugs out. Weep holes will allow water to egress out from the floor.