Alan Scott oven project begins

[astroinfidel]

Hello everyone from rural Quebec. I have just begun a 32 x 36 inch Alan Scott oven build, and will document it here and hopefully find advice when I need it from others that have gone before me. I can see from reading posts here that this forum tends more towards pizza ovens, and many consider the Alan Scott design to be too massive and that it takes too long to heat. This is not a concern to me. I am retired on a bush lot, and my focus is on baking bread. I will be using the book "The Bread Builders" as my guide. I poured the foundation slab yesterday, and am going to keep it wet for at least a week before starting the block walls.

Sorry if the images are out of order. They were not uploaded that way and seem to have gotten mixed up somehow.

Dean

[UtahBeehiver]

Welcome to the forum. We do not see a lot of Alan Scott ovens on this site but we can offer a lot of newer technology and material suggestions to make your oven more efficient. Do take a look at the new barrel oven that Karangi Dude is building, he does a lot of bread and non pizza cooking and his build is top notch and he teaches WFO cooking.

[astroinfidel]

Hello Russell,

And thanks for the welcome. I would actually be curious what the best modern material would be for under hearth slab insulation. I will be using firebricks for the hearth, then under that will be a 3 1/2 inch thick hearth slab for thermal mass, then the insulation layer. The plans call for vermiculite/cement at 6/1 for the insulation layer, but I have heard that there are better alternatives available now. I would like to insulate it very well - as much as 3 to 4 inches of synthetic material if possible. I have been searching online but have not had a lot of success yet.

I will let the foundation slab cure for a week before starting the block walls. I just picked up the blocks today.

Dean

[JRPizza]

I don't know what plans you are following but if I remember right the original plans had an excess of thermal mass in the floor (sort of a floating island), whereas I believe the newer plans have a more reasonable mass sitting on top of efficient insulation similar to the FB oven plans.
Edit - I posted this and when I saved your last post appeared. Having a layer of firebrick sitting on top of and thermally coupled with a 3.5 inch slab will certainly work but will also take lots of wood and longer firing times. Most ovens on this site have bricks laying flat (~2.5") and if more thermal mass is desired bricks are laid on edge for 4' of depth. These ovens produce some quite long cooking times. I didn't see if you are planning on doing commercial type baking, but if not you might want to consider cutting back on the floor mass.

[UtahBeehiver]

CaSi board, minimum 75 PSI compression rating recommended, there are may brands out there, Thermo Gold 12 is one, FB store uses AlSi board as well, It is substantially more costly than v or p crete. Again, look at KDs build, he is doing it right, using both CaSi and V/pcrete.

[astroinfidel]

Hi JR pizza,

I guess how much mass is considered excessive depends on a few things. I have free unlimited firewood, and I am going to be baking mostly bread. I think if you are going to be mainly using the oven for pizza the hearth mass would be considered excessive. But I am building this for bread, and for the long term. It is located on land that has been in my family for over 100 years, and I hope it is still being used here for baking in another hundred or two. I likely won't use it commercially, but I want the option of someone being able to if so desired sometime in the future. And I love the idea of firing it once for the day for bread, and then being able to cook dinner without refiring it days later. So I will be happy to have the hearth mass. I am retired and have lots of free wood and the time to let it heat up, so it just isn't an issue for me.

I have been using my cousin's Pompeii style oven that he built from FB plans. It is a big one..48 inches, and when I fill it and get good steam from the loaves, it produces fantastic bread. But even when fired for about 5 hours, I can't get a second bake out of it. I am down to 400 F by the time the first batch comes out, and it doesn't recover. So for my purposes, I did not find it had enough thermal mass.

Dean

[astroinfidel]

Thanks Russell,

I will check out those insulation leads.

Dean

[Gulf]

I will be using firebricks for the hearth, then under that will be a 3 1/2 inch thick hearth slab for thermal mass,

Have you thought about turning the fire brick on edge. That is 4.5" of thermal mass? Many bread bakers have done this. Going with your plans, make sure that the "hearth slab" is a refractory blend. Otherwise, if you were ever able to heat saturate it, it will spald. Those tiny little explosions will loosen the connection with the floor brick making it even harder to heat. Imo, you need to rethink this.

[astroinfidel]

Hello Joe,

The bricks will be on edge, and the plans do call for refractory mortar for the hearth slab. What exactly do you feel I need to rethink?

Dean

[Gulf]

Dean,

The bricks will be on edge, and the plans do call for refractory mortar for the hearth slab. What exactly do you feel I need to rethink?

Imo 8" of floor seems like a bodacious amount of real estate to heat saturate. But, it sounds like you've got this. Let us know how it performs.

[astroinfidel]

Hi Joe,

I just happen to be at a time and place in life where I have unlimited firewood, and lots of time at hand. That changes the equation a bit I think. Let it take 10 hours to saturate! From what I am reading of those who have built this oven, they are able to do 6 loads of 10 to 12 loaves of bread on one firing once saturated, then use it for cooking dinner days later, and as a slow cooker later still. Without the luxury of time and lots of wood literally laying around, the thermal mass I am building to probably wouldn't make as much sense. I also like the idea of a family member of the future having the option to use the oven for a small bakery if desired. So bring on the concrete and thermal mass.
And Russell, I have asked for a quote from the manufacturer of Thermo Gold 12 to cover the 56x48 inch under hearth area that I need. I asked for a quote for 4 inches thick, and told them I want to pour a 4 inch slab over it for a hearth for a bread oven. I'll let you know what they say when I hear back from them. And yes I expect it to be a lot pricier than vermiculite and cement!

Dean

[JRPizza]

It's awesome that you are going into your build eyes wide open. We will all watch your build with great interest and hopefully you will continue to post/contribute after the oven is in use so we can all learn about how oven's perform with copious amounts of thermal mass .

[SableSprings]

Hi JR pizza,

I guess how much mass is considered excessive depends on a few things. I have free unlimited firewood, and I am going to be baking mostly bread. I think if you are going to be mainly using the oven for pizza the hearth mass would be considered excessive. But I am building this for bread, and for the long term. It is located on land that has been in my family for over 100 years, and I hope it is still being used here for baking in another hundred or two. I likely won't use it commercially, but I want the option of someone being able to if so desired sometime in the future. And I love the idea of firing it once for the day for bread, and then being able to cook dinner without refiring it days later. So I will be happy to have the hearth mass. I am retired and have lots of free wood and the time to let it heat up, so it just isn't an issue for me.

I have been using my cousin's Pompeii style oven that he built from FB plans. It is a big one..48 inches, and when I fill it and get good steam from the loaves, it produces fantastic bread. But even when fired for about 5 hours, I can't get a second bake out of it. I am down to 400 F by the time the first batch comes out, and it doesn't recover. So for my purposes, I did not find it had enough thermal mass.

Dean

Welcome Dean! Sorry to come in a little late to this thread, but I do find it interesting that your cousin's oven doesn't store enough heat for a second bread bake. I have a 39" Pompeii style oven with 3.5-4" of 5:1 perlcrete insulation under my cooking floor and normally bake about 20 loaves (in 3-4 loads). I have a full firebrick cooking floor and wish I could have put in the superior CaSi insulation board instead of the perlcrete. I bake my baguettes at 575F and finish with a load of whole wheat type breads at 475-500F an hour or so later. I now fire my oven late in the evening (overnight-slow burn/reduced draft) before baking and clear any remaining coals/ash mid-morning the next day. The dome is always cleared by morning and I usually have to open the oven for a time to cool it down to bread baking temps. That cool down period for me can take 1-2 hours (low draft) and I'm sure you will have to work out a firing schedule that allows for the cool down (and includes the seasonal outside air temps ). I've attached a temp profile below from my first method of firing in the morning of bake day, where I don't believe I was saturating my oven bricks to full thickness. I think you will want to take similar readings of your cooking floor after the oven has been cured to develop a similar temp graph to settle on your cooking/baking windows.

Normally, I throw in a chicken or dutch oven full of potatoes & onions after bread bakes and have had no problems having a fine meal from them. I know that others with much better insulation (the newer materials) and normal full brick thickness, have reported cooking temps several days after initial firing. Insulation & an insulated door are MAJOR factors in retaining heat in any WFO.

As others have said, I'm looking forward to following your build!

[astroinfidel]

Hi Mike,
And sorry to be so slow getting back to the thread myself. My cousin doesn't have his oven permanently set up yet, and it is just the slab with the oven on some stacked blocks. I think he has 2 inches of ceramic insulation under the hearth firebricks, but then I think it is just the thick concrete slab. So this may be robbing him of some heat. He also does not have a very efficient door, so that likely doesn't help either. I think he has 2 inches of ceramic blanket and a few inches of Perlite concrete on top, and that is all.
I have been busy with the oven build. Here are 6 pics and I'll follow with 6 more in a new post as 6 seems to be the limit per post.

And I love your temperature data! I will be installing two thermocouples in the dome cladding so I can speed the learning curve and just geek out keeping track of it. .
Dean

[astroinfidel]

Here are a few more pics, including a dry run with no mortar. I have just set the hearth bricks in a 50/50 fireclay/sand mixture, and will soon start the walls. I did not pour the slab with alumina cement after all. The day before while doing some last minute reading I found the following on an engineering site:

"High alumina cement concrete is one of the foremost refractory materials but its performance varies with the range of temperature. Between room temperature and about 500°C, concrete made with high alumina cement loses strength more than concrete made with Portland cement, then up to 800°C the two concretes are comparable but above 1000°C, high alumina cement gives excellent performance."

Here is the link: http://www.engineeringenotes.com/con...chnology/31082

So it appears at the temperatures that the slab is likely to encounter, Portland cement is as good or better than alumina cement. And alumina cement starts out weaker than Portland to begin with. And after reading about the process of "conversion" that degrades and weakens alumina concrete, I decided to stay with Portland. As aggregate I am using only crushed granite to reduce or hopefully eliminate spalling. Not as good as traprock or some other igneous rocks, but hopefully will be able to take the heat that it will see in the slab and cladding.

I poured 5 3/4 inches of Perlite concrete insulation, then 4 1/2 inches of granite aggregate concrete for the hearth slab. That gives me a cool 9 inches of thermal mass when I include the 4 1/2 inch firebricks on their side. That should store enough heat for a loaf or two.

Dean