Days 7 and 8 - First Half of Facade Bricks, Granite Slab, Arch Form and Back Walls

So today was a big brick laying day. And the whole purpose of it was to build up the facade bricks because our granite slab relies on it to rest on. On top of the granite slab goes some bricks necessary to build up before I finish the dome. So that is what we did today, lay a few hundred bricks to that I can place the 8 necessary ones in position so I can proceed with the dome (it actually isn't critical until the front courses of the dome go in, you will see which bricks I am talking about in the next post though). So it was a long day and if there is anything I learned from laying brick all day long, it is that next time I am going to wear gloves. By the end of the day my fingertips became very tender and crackly to the point where my fingerprints were disappearing. The combination of rough bricks and what felt like portland cement finger corrosion was not pleasant. 

Lay up the corners first, and fill in using a mason's line 

Using a mason's line

An old angle iron works perfectly to bridge the gap.

The combination of the lifelong bricklayer and the never-before bricklayer made for a good team.

After finishing the facade bricks, it was time to work on getting that granite cemented to the oven once for all. The first step was to fill in the gap from the hearth bricks to the facade bricks. Now, remember this picture? 

Look at the rebar sitting there in the front of the oven, right where I need to lay some fill brick. What an inconvenient place for them. It would have been much better to have the front and back rebar in the grooves and the side rebar laying on top of the block. So if you are going to build an oven, do not follow my example unless you have to. In my case, I had to do it this way because the lintel had rebar very close to the top. If I cut grooves, I would have had to cut through rebar. But here is the beauty of the situation, a standard firebrick fit exactly in the spaces in between these pieces of rebar. So what you see in the next picture is two courses of firebrick, and then some red brick. Also in the above picture, remember the fireclay/sand mixture we used to set the firebrick on? Since it has no cement in it, if you put your extra in an airtight bag, it will not harden. This is what I did after laying the hearth bricks, and here in the picture below, I am using these leftovers to fill in my gaps.

Making a relatively level surface for the slab to lay.

Slop some oven mortar on.

We gave it a slight downhill slope so that when it rains, the water moves away from the oven.

After the slab went on we went through a somewhat lengthy process of making a form for the slab. Unfortunately we do not have any pictures of making the form. What The Bread Builders says to do is to just place your bricks on a board you will cut your form out of so that they are in the shape of an arch. Then trace that shape, cut it out, and you have your form. As easy as this could have been (and probably perfectly adequate), it was utterly unsatisfactory to me. I wanted a precise arch. But what kind of curvature should an arch have? I didn't know for sure, so we decided on using a portion of the most perfect shape - the circle. Now the most efficient brick oven has a door height which is 63% of the dome height. All I have to say is some complicated math went into making an arch form with a base of 23.75 inches and a height of 6.25 inches and having it be a part of a circle. I will not attempt to explain it here, especially if just fudging an arch line is good enough by professional standards. Another way I heard of doing it is to hold a string at both base points, and letting it hang down to the height point. Spray paint over the string and there you have it, the shape of your arch. We tried it this way at first, but it just seemed a little too imperfect. So maybe this was just our personal obsession, but we made a pretty perfect-shaped arch form. We used two 2x8s, cut out with a bandsaw, and held together with two 2x4s to make a gap. You will see it in action in the next post.

Once we have the arch frame, I can put it up to the oven walls and see how many bricks I need to lay for the back wall so there are no gaps in the oven. This was pretty simple and straight forward brick laying.

Now we are all ready for the arches!

Day 6 - The Walls

Like I have already said, before cementing in any of the walls, make sure you know exactly where you want any of the bricks. This is my last and final mock-up. After it all is set up, I marked each brick with a pencil, even down on the sides of the firebrick as well where each brick should lay. The most crucial bricks are the door jam bricks. See below.

This mock-up is even a slight modification to the previous one. I set back the
door jam bricks to more easily tie into the facade without having to cut bricks.

Carefully mark where the bricks will go

The mortar used for this project is a very strong and fast-setting mortar (10 parts sand : 3 parts cement : 1.5 parts fireclay). To say the least, this was a very frustrating endeavor for me, but with a little practice, I became better at it by the end. Especially if using portland, it really sets up fast once it touches a brick. Also, the more you tamper with it, the harder it will get. At times, it seemed to set after 15 seconds of fiddling with tapping the brick so it is in just the right position, leveled to itself and to the surrounding bricks. This did not give me enough time to get it just perfectly in place and I would have to take the brick out, and throw away the mortar because it has already become set and immaleable. So from all my frustrations, I feel like I can give a few pointers. Don't neatly tamp the mortar before you place the brick on it... just slap it on there as loosely as possible and let the brick smash itself into position, but get it to the correct mortar joints quickly, always keeping the level and rubber hammer handy. And it doesn't just matter how fast you get it into position, it matters how many times you tap it - the more you tap it, the faster it will set - so no unnecessary baby taps - it will go solid before it is in position and you will have to take it out and start with fresh mortar. Also, I dunked the bricks in water for a few seconds and let them drip dry a few minutes before using them - this helped a lot.

The four pictures below have different ways I dealt with the big mortar joints at the corners. The first three of these I did, I just filled it in with a lot of mortar. All of these ended up with fairly large vertical cracks, and one of them actually lost its bond to its neighbor and I had to redo it. So for the last 6 of these joints, I filled them in with angled brick pieces and these ones did not crack because they has more or less normal mortar joints.

One large solid mortar joint. Notice the crack on the right.

I filled this one in the brick pieces and it worked a lot better.

You cannot tell that the big joint on the right has brick pieces in it, but it does.

I took the bottom supports out. Fortunately it held its own just as expected! 

Progress to date 

So next is pouring some cladding about 3/4 up the wall so the arches do not push them outwards. But before we start on the arches, We need to lay the facade brick on the bottom half of the oven because our granite slab will rest on this brickwork, and I need to lay some brick on this granite slab before I lay any of the arch bricks. So next day of work will be collecting some more free bricks and laying up the walls to hearth level.

Day 5 - Firebrick Hearth

The day after we poured the slab, we took the frame out and continued to let it cure for about a week, not because it needs to cure that long, but because it has been rainy. Here is a good view of the poured hearth. You can clearly see the rebar grooves in this picture. 

In the meantime, I did quite a bit of research on firebrick in the area. For these ovens, it is recommended that you find low-duty firebrick (ASTM C 27). The best way to figure this out is to call your firebrick providers and ask. Many building suppliers will not know... a firebrick is a firebrick to them. But they can find the information from their provider as well. Low-duty firebricks are usually cheaper too (I paid $1.30/brick for mine). Medium-duty and High-duty bricks will be more expensive. Low-duty bricks are also softer and will likely have chips and/or small cracks in them with semi-rough edges. Medium or high duty bricks will be crisper, harder, and less likely to chip or crack when you handle them. So why use low-duty bricks? My understanding is that it is less conductive to heat. What I think of is making a pancake in an aluminum pan (high-duty firebrick) compared to a stainless steel pan (low-duty firebrick). In the aluminum pan, and pancake will burn a lot faster because the heat moves through it so well. In the stainless steel pan it will cook slower with the same amount of heat, it is just transfered at a slower, less intense rate. So with bread in an oven, a high-duty firebrick will burn your loaf before it is really done cooking. If you are making your oven just for pizzas and not for bread at all, maybe medium-duty firebrick will work just fine, if not better. Also, low-duty bricks are safe up to 2000 degrees F. You will never get your bricks to this temperature, so nothing to worry about.

Before I did anything, I laid all the bricks on the hearth and made a mock-up. This is what I came up with, but if you scroll down to the later pictures, I changed it just a bit. Now I know how I want the firebrick laid on the hearth slab, so now once we have a nice day, I now know how exactly to lay.

To lay the firebrick on the hearth, you have to make a 50/50 mixture of sand and fireclay. Add just enough water to make a thick paste.

Sand/fireclay mixture. 

Then spread it over the hearth at about 1/4 inch thickness. Make sure it is as level as possible, this will prevent you from adding or taking away the clay with each brick to make it level with the rest. This stuff was actually very hard to spread, but it is doable.

Getting it as level as possible 

The sun decided to come out, so I put the canopy over so the clay won't set on me.
It does last a while however. It didn't seem to really set until you lay the water-sucking brick on it,
but what was left in the sun set as well.

I started with the front bricks and worked my way back. You should know the exact distances the bricks should be from all edges because you did your mock-up already. So be measuring the whole time. It is also good to draw a line down the middle for a reference point. Every single brick you lay you should level both ways.

Another thing to remember, especially if you use the recommended low-duty firebrick, is to always lay the neatest, crispest side up. The bricks along the sides and back can be your worst quality bricks because they just get covered up by the wall anyways. If you are using firebrick for your walls and arch, you have more to choose from to get the best ones for the hearth. If you are just using firebrick for your hearth, it would be a good idea to pick out your bricks yourself at your supplier to avoid getting badly chipped ones.

In my plans, the first bricks come all the way to the edge. 

Checking for levelness. Notice that the clay was spread with a notched trowel.

All done!

I wanted to make my oven door 9-inches high, so I used firebrick at that point instead of red brick. I will also need to cut myself a slightly longer piece of angle iron. From the first picture, I also extended the oven one brick length, bringing the door all the way up to the granite slab. The next nice day, I will mortar in the side walls

It's starting to look like an oven!

Been working on cleaning off reclaimed bricks this whole time!

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.