Day 4 - Pour Slabs

Step one for today: build a frame for the hearth slab. I measured the size I want the slab to be, then cut 1x4s to length and screwed them together (put to screws in, but in the top half so that you can back the screws out once the slab is poured and knock out the boards). Then, to know where to make notches, I set the rebar in place very carefully and marked exactly where they go on the block (Only two of the four sides need the notches so that one direction of rebar can run above the other direction. Today I also had to readjust some of the grooves to go a little deeper because the top run of rebar was resting on them instead of the block). Then I took the rebar out, put the frame in, marked where the rebar will go, and then cut out the notches.

To make the vermiculite concrete, I used 6:1 vermiculite : portland cement. Make sure it is mixed very well before adding water. Also, we needed almost twice as much as we thought we needed from calculating square footage. I'm not sure why this was, I guess the water really pulled everything together.

Mix the dry ingredients thoroughly. 

When adding the water, I would suggest doing it with a fine spraying hose because the vermiculite will absorb a lot of water and every time you add water it washes the cement from the vermiculite. So it is good to mix the water in right away little by little so it all doesn't just go into the vermiculite. But maybe this doesn't matter.

Slowly adding water and mixing it in little by little.

That's about right

We poured half of the slab, then put the reinforcing wire in, and poured the rest. Usually you would not have to do this, but the wire we had had pretty small holes, so in order to insure that cement got down to the bottom sufficiently, this is what we did. 

Note: The vermiculite slab is 2-inches thick. The hearth slab is 3.5-inches thick.

We let this sit for about an hour before pouring the hearth slab.

Tying the rebar together. You can see better in this picture, the "vertical" rebar are in grooves,
yet the "horizontal" rebar are simply sitting on the block. This puts the bottom rebar 1-inch from
the bottom of the slab and the top rebar 1-inch from the top of the slab.

Our concrete mix was 3:2:1 Gravel:Sand:Portland with a little extra portland for just a bit more strength, knowing that with heat, it is going to lose strength.

We filled the wheel barrel full full and then needed another half batch
and ran so slightly short. So the edges are just slightly low, but this will
not matter and does not compromise the structure at all.

It was sunny and windy, so we covered it to slow the curing.
Slower curing makes stronger concrete.

So tomorrow we take the frame away and let it cure all day. Then the next day we will lay the firebrick and walls.

Day 3 - Prepare for Pouring

Still doesn't look like an oven, but we are making progress. So I did decide to cement in the cross supporting block, and then put an additional 4-inch block to bring it up to the level I want to pour the insulating vermiculite concrete. Like all the rest of the pictures you will see in this post... I am using what I have laying around. You might find a much better way to accomplish the same task. My main goal was to get the top of the block to a height 4 inches from the top. This will leave room for a 2-inch vermiculite concrete slab, and half of a 3.5-inch hearth slab (you will see more of this later).

Hard to see from this angle, but it does not quite touch the back wall,
it is about 2 inches short

The next step was to build a platform to pour the concrete on top of. I built two platforms, one in the back and one in the front. Now my plans evolved to the point where once the concrete is poured, I am going to leave the plywood there forever stuck to the underside of the poured slab. For the back section, I have no choice in this matter... once the slab is poured, there is no getting back there to retrieve the lumber. As for the front part, it was just easier in my case to use the supporting block as a lip, and then three additional supports on the other end (see pictures). This made it incredibly secure without one nail or screw. If you look at the picture below, I had to rig up a method where I will be able to knock out a section of wood or block (once the slab is poured), so that they do not have to stay there forever as well. Again, using what I had, I was able to make something very structurally sound.

A 2x4 going across the three supporting legs greatly
increases its strength for the plywood going on top.

The plywood is now resting very securely.

 Today I bought 8 pieces of rebar: four 44-inch and four 48-inch of 5/8-inch rebar. The rebar should be at least 3 inches from the edge of the hearth slab, and no two rebars should be less than a foot apart. So make sure to do your math, measure a couple times, and then you can start making the grooves. I used a borrowed saw which has a diamond blade on it for cutting through concrete. Wear plenty of face protection... portland cement is a nasty thing to be breathing in, and these saws are loud!

Making grooves for the rebar

It should have a little "wiggle room" for when it expands a little.

Now this is completely my own thing here. I don't want the board to start
sagging someday. So I put nails through to secure it to the concrete.
Remember, I am leaving them in there forever after taking the
supporting legs out from underneath.

Put the wire mesh in for the vermiculite concrete layer. I snipped a bunch of wires
to better secure it to the hearth slab which will be poured on top of it.

There is more to come tomorrow or the next day (whenever the rain stops). We will be pouring our vermiculite concrete, make a frame for the hearth slab, and then pouring that as well.

Day 2 - Lintel and Cross Supports

Today we brought the 6x8 concrete lintel over and laid it in place. I also mixed up some more mortar and filled the last course of block solid. To prevent it from going all the way down to the first course, we stuffed newspaper down in the third course... it worked beautifully. Yesterday we had some leftover mortar, so we filled all 4 corners solid as well. I don't think this would be absolutely necessary for this size oven, but since we had leftovers, we used it in combination with scrap pieces of block. However, with the heavy lintel, we did want to make sure to fill the front two corners.

As far as the cross supports, you will not find this in The Bread Builders at all, and I am probably overbuilding the oven. The reason I am doing it is two fold. First of all, I am planning on pouring the hearth slab using portland concrete rather than refractory concrete. When portland concrete is heated to 750 degrees F it loses half its strength which does not return when it is cooled. Knowing that the hearth will be getting very hot (although unlikely to get to 750), it will therefore be getting weaker. So I am just taking precaution (and I have extra block laying around... if I had to buy the block, I probably would not put this in). The second reason is that this was one of Alan Scott's later improvements to his commercial ovens. These two pictures below are of one of the first ovens he built, and notice how the hearth slab has sagged over the years. This reinforcement would hopefully prevent such sagging.

It is hard to notice, but there is a 1-2 inch sag in the middle.

You can see the sag a little better from below.

I also did not bother mortaring in these reinforcing block. However, I may do it for two reasons: First, to keep wasps from finding holes and making a giant hive in the back of the oven. The second reason is I need to raise it 1.5 inches for the vermiculite slab that will be sitting on it, so the mortar will be just enough to do that. Ok... here is what I did today...

The lintel was actually 1 inch short, but that is no big deal, it will just be covered up anyways. 

I left a space there in the lower right for a piece of rebar which will support the slab.
When I figure out exactly where it will go I will put more mortar in there, but still leave
some wiggle room so the expanding rebar won't crack the block.

Day 1 - Laying Block

Over the past week, I spent some time rounding up some materials to start building. We were able to reclaim some 6-inch block. Although my plans were made using 4-inch block, you can't beat free... therefore appropriate adjustments were made. This project here took just under 40 block, however you will need more if you follow the procedure in The Bread Builders (not only because they plan for a larger oven, but also because we took appropriate shortcuts). How we managed to have fewer block was because instead of having two angle irons to span the gap in the front of the oven (where we will store wood), we are going to put on a 4 foot concrete lintel across the opening, also reclaimed (As much as you can, used reclaimed materials. Ask around and let your need known, especially for these parts of the oven you won't even be able to see). 

Yesterday we went to get some sand, portland cement, and masons lime. To say the least, they gave us more than our share of sand and I am sure we will be using it on our big oven someday. We used a general mortar mix: 4 parts sand, 1 part lime, 1 part portland cement. 

They probably loaded us up with an extra 1/4 ton of sand.

It is nice when your Grandfather is a retired brick layer.

Laying our first course of block

Onto the last course, leaving room for the 6x8 inch lintel. 

Another perk about using reclaimed block is the possibility of a multi-colored wall!
We are letting the block cure before we put the heavy lintel on tomorrow.
I'm not sure if it was necessary, but we filled the cores where the lintel will sit
in order to make it more solid.

Just a general disclaimer - this patio has a deep footer in it, so we know it is plenty stable. If you are going to build an oven in your yard, you will either have to follow the guidelines in The Bread Builders, or at least know that you are building on a stable surface. But I am not much help since our foundation is already conveniently there. 

A Starting Point - The Patio Oven

Today I went out to the patio and measured the exact dimensions for the oven and laid some block down to get a visual image of the location of the oven. I was suddenly hit with a great wave of anticipation.

But the point I am at now (just about to break ground with construction), seems like it will be the easier part of the journey (however, I could be wrong). The hard part was understanding all the details and painting a comprehensive picture in my brain so that I could more or less proceed without much confusion as to why or how to do something. Unlike most "patio oven builders" out there, I am approaching at this project somewhat backwards because I already have 2 years of experience working on a much larger commercial brick oven. So I already understand HOW the oven works from firsthand experience, but I am now learning WHY it works so well. I can't emphasize enough to do your studying before you break ground if you are going to follow the Alan Scott model for a brick oven.

An absolute MUST have for oven building is Daniel Wing and Alan Scotts book The Bread Builders. I also learned a considerable amount from Kiko Denzer's Build Your Own Earth Oven but have decided to stick 100% to the method laid out in The Bread Builders, mostly because we are preparing ourselves for making a big one some day using more or less the same methods. There are some confusing parts to the book, especially with the pictures and the order they are shown, so I will do my best to post pictures with descriptions of what we are doing.

The oven we are going to build, however, is not the same size as what is shown in The Bread Builders. They suggest building an oven which is 32x36 inches. The oven we are building will have a baking surface of 24x28 inches. However, the method of building and the guidelines in the book will be more or less identical with some slight modifications which I have gained from other oven builders.