So far, this pizza oven project has been rather uninteresting.  That is, unless you have a special place in your heart for concrete.  Going to school with some engineers, I definitely know this strange species of human being does exist.  But me?  This concrete stuff is just a means to the end goal.  Now that the oven stand is complete, there is finally only one more concretious (every now and then, i like to invent new words) step:  The Hearth.

Here is the stand before we start with the hearth.

Currently, the oven base is a big hollow rectangle.  It isn’t exactly pizza oven ready yet.  How can the brick dome stay on the oven  stand without support?  Simple.  It can’t.  That is where the hearth comes into play. The hearth will span the concrete block oven base and provide a level, strong base that will support the rest of the oven.

There are two parts to the hearth.  Each of these two different layers serve different goals:  Keep it up and keep it warm.  Let me elaborate a little bit.  The first (bottom) section of the hearth will provide the structural support to hold everything else up.  This is made of regular concrete.  Unfortunately, concrete doesn’t do so well when exposed to all of the heat up/cool down sessions (thermal cycling) that the oven causes.  When burning a wood fire in the brick oven that we are building, temperatures can easily reach 800 degrees.  At these temperatures,  it wouldn’t take long for the concrete to lose it’s strength.  What would happen then?  Bye bye pizza oven!

How do we protect the concrete from the temperature extremes seen in the oven?  We’ll keep those hot temps in the oven where they’ll do some good.  How?  The same way that we keep hot temps in our house in the wintertime – insulation.  The second section of the hearth is an insulation layer to keep the oven hot and the concrete cool.

Materials & Cost

Ok, so here are all of the materials that I used for the hearth.

1. 80lb bags of concrete:  17 @ $3.60 = $61
2. 1/2″ rebar, 10 ft sections:  9 @ $5.20 = $47
3. 4 cu ft. bags of vermiculite:  2 @ $12 = $24
4. 94lb bag of portland cement:  1 @ $12 = $12
5. 2×4 8ft boards for supports:  4 @ $2.83 = $11
6. 2×6 8ft boards for form:  4 @ $4.79 = $19
7. 7/16″ sheet of OSB:  1 @ $8.87 = $9

The hearth requires a lot more of the same stuff that I have been using on the foundation and stand.  There is one additional special ingredient:  Vermiculite.

This is a classic display of my pure strength! Actually, vermiculite is super light and airy (hence it's use for insulation)

What is vermiculite?  Vermiculite is used a lot in the horticultural world.  It lightens up soil and prevents compaction.  It is made from crushed rock from some special mine.  I don’t really know all of those details, but here is what I do know.  This stuff is really light, airy, and makes for good insulation.  It is the main ingredient of the insulation hearth (keeps the heat inside of the oven).  We’ll also be using it later on to insulate the rest of the oven after we are done building the dome.

Structural hearth

The first duty of the hearth is to support the oven above it.  To do this, a reinforced slab of concrete will be poured directly over the oven block stand.  The structural concrete portion is 3.5″ thick reinforced with 1/2″ rebar every 12 inches.  Before pouring the concrete hearth, I had to build a wood stand and form to hold the concrete as it cured.  Most of the details are in the pics below, but I’ll give you a couple of pointers on things that worked well (and some that didn’t…)

Here is what worked pretty well:

1.  I cut some wood shims so that I could fine tune the height of this form.  The bottom of the hearth doesn’t really have to be completely level, but it doesn’t hurt.
2. To hold the rebar in the middle of the 3.5″ thickness, I used broken up pieces of block from the leftovers on the stand.
3. To keep 2×6′s on the stand from bulging out from the pressure of the concrete, a ratchet strap worked perfectly.

These wood supports hold up the plywood, which in turn holds the concrete as it sets.

Ready for the 3.5" thick concrete hearth. The ratchet straps will keep the 2x6's from builging.

At this point, I am about tired of mixing concrete. Bag after bag after bag.  But there is light at the end of the tunnel!   As soon as this step is complete, the fun part begins.  So that gave me some motivation to keep charging.

Pouring the structural hearth for the pizza oven. Remember when I left some empty cores when I built the stand? These are getting filled in now.

Insulating Hearth (Vermiculite)

Since it took me a lot of my Sunday to build the structural hearth, I gave up after I completed the structural section.  Some people pour both the structural and insulation on the same day.  These people are either crazy, much faster than I, had help, or all of the above.  Actually, since beginning this project I have realized that anyone who builds their own pizza oven has to have at least some craziness in them.  It is a long, long project that takes up a lot of evenings and weekends.  But it will be worth it!

This second phase of the hearth, the insulating hearth, will keep the heat from the oven inside and protect the structural concrete from getting extremely hot.  It is made of 7 parts vermiculite, 1 part cement (both by volume), and water mixed in until it is the consistency of oatmeal.  This part only has to go directly underneath of the oven.  As you can see below, I sectioned off some of the front because that is where the landing will be (where the eager friends/family will line up their pizzas ready for the oven).  I can’t wait until that day!

The structural hearth is complete and I am now forming up the vermiculite insulating base. THIS BASE MUST BE LEVEL!!!

Unfortunately, I didn’t get any pics of actually pouring the vermiculite base.  One evening after work, Lara and I were hard working individuals into the night under the glow of our floodlights.  She measured out the ingredients into our wheelbarrows while I mixed and poured.  Our system was working so well that we didn’t have time to take pictures (and it was pitch black out!).  After mixing this stuff up, it may feel like it will never setup solid.  But, to my slight surprise, it ended up setting pretty hard.  Oh yea, if you didn’t read the caption above, this part has to be level.  That is, unless you are aiming for lopsided pizzas!

And for a sneak preview of the next step, the pizza oven floor, I’ll let you see one brick…

Two days after we poured the vermiculite base, it was hard enough to start laying bricks on top of.

About a year ago, I saw this awesome sign at the end of our street. A 4×8 sheet of plywood with some glorious red paint that scripted these two words: FREE BLOCK. And right next to that sign, there was a large pile of gray concrete block. Oh how two words could mean so much! I rushed home (the whole 2 miles), got my truck, went to this guy’s house, and started loading that block right into the back of my truck. Heck, the guy even came out and helped me load. Apparently, his wife said it was time for that block to go. He was happy. I was happy.

After all was said and done, I had taken home two truckloads of block. After using some for various projects (maple syrup boiler and a compost bin), I had about 20 good ones left. Fast forward a year. My wife tells me that the block that I picked up a year ago was starting to look rather redneck in our side yard. Funny how things go around, isn’t it?

At the time, I had no clue how much a concrete block was. As it turns out, it wasn’t really that much of a money saver. At $0.98/block, 20 blocks are worth a grand total of about $20. But am I glad that I picked them up? Heck yea! These blocks have served as a motivational piece for our pizza oven. And now, after a year of sitting in the side yard, I am ready to use them up for their original intention: The Pizza Oven Base.

The oven base serves two purposes. First, and most importantly, it supports everything above it. The hearth rests on top of the block stand, and the actual brick oven section rests on top of the hearth. Second, the oven base is a storage area for the wood (or anything else that you want to keep down there).

Materials & Cost

The materials that I used for the oven stand are below. These are the total materials required. Since I already had some block, I actually bought a little less than what is below.

1. 8x8x16 grey block: 52 @ $0.98/block = $51
2. 8x8x8 grey block: 2 @ $1.02/block = $2
3. ½” rebar, 10’ sections: 5 @ $5.20/pc = $26
4. 80lb bags concrete: 14 @ $3.60/bag = $51
5. 2” x 2” by 1/8” angle iron, 48” long: 2 @ $12 = $24 (thicker is better here, but I went cheaper. 3/8” is probably the best option, but expensive)

Total cost for the pizza oven stand: $154
Running total (foundation, stand): $364

Tools

Building the stand doesn’t require many tools, and most of them I already used on the foundation. The only new thing needed is something to cut the rebar. Since I already had an angle grinder, that’s how I cut the rebar (that angle grinder also comes in handy later in the project when I cut bricks for the dome).

Lay Out the Base

Since I am not one of those people who absolutely gets everything right on the first try (although I like to think I am, there have been way to many situations that have proved me wrong), I decided to dry stack my block on my driveway as a test run. This was good so that I could get a feel for how big this pizza oven was going to be. I actually did this last fall before pouring my foundation.

Here is my dry test run to make sure the size works. Those bricks were back before I decided on the dome style.

After the test run was a success, I measured the block stand and then made the foundation slightly bigger than the stand. As you can see from the above trial setup, the final stand is 4 blocks wide, 4.5 blocks deep, and 4 rows high.  When actually starting the real stand, I knew that it was very important to get the first course right.  I double checked, then triple checked that the first course was both level and square.  After all, if I screwed this part up, there wasn’t much hope for me in the rest of the project.

Laying out the first course of block. See the level? It's important! Make sure the first row is both level and square.

Although you could mortar the whole block stand, I took the route suggested in the Forno Bravo plans. I dry stacked the entire stand, dropped a piece of re-bar into every other core, and then filled it with concrete. For the rebar that is being dropped into the cores, cut 4 of the 10 ft pieces into 4 equal 30” lengths (if my math is right, that gives 16 pieces of rebar at 30” in length). I cut a couple of pieces incorrectly so the pictures show a little bit differently than what I could have done.

Put the empty concrete bags into the holes that you don't want concrete going into.

The oven stand is complete and ready for the hearth. Notice some missing cores? I'll fill those in when I pour the hearth.

The only other piece of the stand that I didn’t mention in the front span.  Since the blocks are spanning over the “door” to the storage area, the angle iron is required to hold up the blocks.  Since I was a cheapo on the angle iron (1/8″ vs. the recommended 3/8″), I decided to give some extra support and put some rebar across the span.  Along with some concrete, that should be plenty strong enough.

The front span was hollowed out and rebar placed for extra strength.

That’s it for the stand!  Next up:  Pouring the Hearth.  When I go to pour the hearth, I will fill in the rest of the holes, along with the front span above. By pouring some of the cores at the same time as the hearth, it cures all at once and becomes much stronger.  Rather than 2 separate pieces, the hearth becomes “at one” with the stand.

Pizza oven stand completed and ready for the hearth

It has been a long time coming, but the time to build our pizza oven on our patio has finally arrived.  Similar to so many other DIY projects, the beginning is definitely not the most glamorous part.  Instead, it is simply the foundation of the rest of the project.  Without a good foundation, the pizza oven couldn’t exist.

So I actually misled you (a little) in the beginning. We aren’t actually breaking ground on our pizza oven foundation right now. Remember last year when we built our patio?  We built the foundation to our pizza oven at the same time.  We had lots of extra help from some workers (Dad, friends, etc.) so it was a perfect time to put them to good use.  We pay friends with food and beer, we get manual labor in exchange.  Good deal for us? I think so!

Choosing the Size of the Foundation

The pizza oven that we are building is going to be a dome style Italian pizza oven that has internal diameter of 36″.  This is important because all components from foundation up needs to be the right size for the 36″ oven.

Based on the plans from both The Bread Builder’s book and the Forno Bravo plans, the size of this foundation needs to be about 70″ wide by 80″ deep.  This leaves some extra room on the outside of the block stand for finish materials.  Here is how it breaks down:   36″ internal oven diameter + 9″ oven firebrick + 12″ insulation = 57″.  That leaves about 6 inches on each side to put on finish materials.

Materials & Cost

Here is everything that we used to build the foundation:

1. 80lb bags of Quickrete:  35 @ $3.60/bag = $126
2. 1/2″ rebar, 10′ ft sections:  4 @ $5.20/pc = $21
3. Stone base:  We bought a whole truckload (18 tons) for the patio, but this was probably 1 ton:  ~$30
4. 8ft sections of 2×6 lumber for forms:  4 @ 5.70 = $23
5. Wire remesh: This depends on how you find it.  Sometimes it comes in a big roll.  Other times you can find smaller sections.  ~$10
6. Some spare bricks or pieces of concrete:  FREE

Total cost for the pizza oven foundation:  $210

Here are the tools that I used (of course, if you don’t have them there are always ways to improvise):

1. Tamper for the stone base
2. Wheelbarrow to mix concrete
3. Shovel or hoe to mix concrete and shovel all of the gravel
4. Sledge hammer or regular hammer to pound the stakes for the form

Breaking Ground on the Foundation

The foundation supports the entire pizza oven.  Therefore, it needs to be both stable and strong.  To make it stable, we built a base of compacted crushed stone about 12 in thick.  Yes, this was overkill (normally 3″ is enough), but we had to make it level with the patio.  Since our yard slopes slightly, one side of our patio needed a lot of stone underneath.  The purpose of the gravel is to prevent freeze/thaw from damaging the slab.

The pizza oven is going to be at the back corner of the patio. See how the yard slopes off as you get toward the pizza oven side? This is why we needed 12" of stone underneath the foundation.

Here is a closeup of the future foundation that shows the stone base.

My dad is helping with staking the forms for the concrete foundation. It's always good to have a helper that knows much more than you do.

On top of the compacted stone, we poured a concrete slab 5.5″ thick. This was pretty easily accomplished by building the form with 2×6 lumber.  The slab was 70″ wide by 80″ deep. To save you from trying to do the math, this took about 35 of 80lb bags of concrete. Thankfully, Mr. Doug was there to lend a hand with the mixing, pouring, and screeding.

Doug is mixing up the concrete and helping pour. Extra muscles is always helpful!

Rebar and wire mesh is an important part of the foundation to provide additional strength.  Two pieces of rebar were placed along the outside of all four edges.  One is 4″ from the outside edges and the other 8″ in from the edges.  A sheet of wire mesh was placed on top of the rebar across the whole pad. Little pieces of brick held the mesh and rebar halfway up the slab at about 2.5 inches high.

This shows all of the important pieces of the foundation. Stone base, 2x6 forms, rebar on edges, wire remesh, and screeding the concrete.

Now it’s ready to finish mixing and pouring in the concrete.  The good thing about the foundation is that it will never be seen.  Therefore, you don’t have to make it nice and pretty.  It’s a good thing, because mine was pretty darn ugly!  But, it will do it’s job.  At this point, that’s all that matters.  I’ll worry about cosmetics later.

The concrete has had time to cure for a couple of days after being covered with a tarp to keep in the moisture. Like I said, it isn't pretty, but it does the job!

Next up is building the stand for the pizza oven.