The Foundation

Let me begin this section by saying that I assume you’ve made your peace with your local council, and whatever rules and regulations they have concerning the construction of permanent and occasionally very hot and smoky contraptions (like wood-fired pizza ovens) in your neighbourhood or neck of the woods. Yes? Good. Proceed…

You’ll need to determine the best location for your oven, and I’ll leave that up to you. I needed somewhere level and stable, not too far from the house but not too close, near a permanent water source and with good overhead clearance. You’ll see from my pics that my oven sits right underneath a spreading apple tree – this was a calculated risk I decided to take. I keep the low hanging branches trimmed well clear of the chimney, and I’ve never had any problem with hot gasses from the chimney affecting the tree.

The first step was to level out an area large enough to accommodate the slab footing (1700x1700). I did this by hand with a pick and shovel, checking the ground was more or less flat with a spirit level.

Next I needed to lay out some formwork to keep the concrete in place. I used some old floorboards we had sitting in the shed. You can really use any old flat strait timber of sufficient size – available cheap or sometimes free from scrap yards and construction sites. Scrimp and scrounge – that’s the key!

The boards I used were about 150mm wide, which I figured would make for a sufficiently solid foundation. Okay, so I’m no engineer.

I set up the formwork, holding it in place with some short lengths of steel reinforcement rod (rio rod). When I ran out of rio I simply propped a bunch of bricks up against the boards to keep them in place.

Thankfully two sides of the footing were cut into the earth, the cut surfaces helping to hold the formwork firmly in place.

I used a tape measure to check the diagonals were of equal length (and hence the overall form was square), and made minor adjustments as needed. I wasn’t too worried about how neat the edges of the slab were going to look, as the long-term plan was to pave around the oven right up to (and thus hiding) the foundation.

Once the formwork was set up, I lay down a sheet of old shade cloth. Why? I’ve no idea, it just seemed like the right thing to do. Perhaps it would help prevent excess moisture in the concrete from leeching into the soil, thus enabling it to set more evenly. Sounds good to me!

A large slab of concrete will need some kind of internal reinforcement to stop it cracking up (or so I’ve heard). For this I used old bricks, some of them broken, and some large rocks I found laying around our property. I’ve seen skip bins full of old rubble like this on construction sites and I’m sure a friendly foreman wouldn’t mind you taking a trailer load home with you (if you asked nicely, of course).

Next came the hard bit – mixing all the concrete and dumping it on top. I had to do this by hand, mixing bags of pre-mix concrete in a wheelbarrow, two at a time. I can’t recall exactly how many bags I had to mix. I don’t care to recall how many. All I can tell you is if you have access to a cement mixer, use it, for heaven's sake!

After each barrow load, I tamped down the concrete with a stick, shuffling it into all the nooks and crannies around the reinforcement rubble and removing any air pockets. 

When full, I smoothed the top with a large level length of timber – tamping it, dragging it and sliding it back and forth across the top of the formwork. As you do this, a thin film of liquid cement rises to the top, leaving a nice smooth surface to finish the job.

I let the concrete go off (set) overnight before removing the formwork. You should probably let it cure for a week or so before building on it. As it happens, I didn’t start building the oven base for the best part of a year. By then it was nice and hard, and my back had almost recovered!