Direct Woodfired Oven Build (with a difference)
One of our ovens at The Forge in Mackay, QLD
The Back Story
Like a sucker for punishment, I put my hat in the ring. As Paul Kelly said, ‘I’ve done all the dumb things’.
A new client was looking for a wood fired oven and someone to teach her how to make sourdough, and I fitted both requirements. Not that I have ovens on a showroom floor or anything - over the years I’ve designed and commissioned quite a few wood fired ovens around this country, and from time to time these bakeries change hands or close, or grow, and the ovens come onto the market. As I have learned quite a few times now - when you really need a wood fired oven there are none to buy. And when there is one to buy, you don’t need it. So, having already designed what I thought to be a ‘quick to build’ direct fired oven, I volunteered to fill the temporary woodfired oven market void. I confidently informed my client that I could do it in about 6 weeks give or take.
Only a couple of hundred bricks were needed. And some steel I had lying around for just such a project. I’d built a similar oven a few years back so I roughly knew what to do. What could possibly go wrong?
She will be called 'The Tardis'
Three and a half months later, it’s finished, and it’s lovely. It turned out quite a bit differently to the original plan in some ways - little refinements which became integral to the design. I’m yet to fire it up (days away), but the design is so simple and robust it will be a good oven to use straight out of the box. It’s made from about 95% repurposed material - just the framework, wheels and mortar are from the hardware store, and the rest has been gathered from wherever I’ve been able to find it.
A ‘Direct’ or ‘Black’ oven
I usually design ‘indirect’ or ‘white’ ovens. These are a type of oven which directs the flue gas around the baking chamber to heat it. They are tricky ovens to get right - the methodology for flueing the gas around the chamber can vary in complexity, but when you get it right (and yes, I have) it creates an even heat in the oven. It also allows you to burn virtually any combustible material as the smoke does not enter the chamber. This new oven design is different - it’s an ‘indirect oven’, or a ‘black’ oven, like a pizza oven, but it has a separate firebox at the bottom, with the flue gases running directly through the baking chamber. Thus, the fuel is limited to wood or charcoal.
Baffle in place
Baffle and steam
In order to avoid the issue of too much bottom heat, I’ve developed a combined baffle and steam system which will tame the heat on the bottom deck, and provide large volumes of instant steam, exactly when it’s needed. The baffle system is very important, and over the years it has been the number one wear point in the ovens. I’ve designed this one to be easily removed and replaced. It also has a lot of thermal mass so it creates a steady base heat in the oven.
The oven is a vertical deck style, and the footprint is less than a square metre. It has 5 ergonomically arranged shallow decks made of cast steel BBQ plates. 4 of these plates can be easily slid out and replaced with a rack for smoking or drying. It will hold 20 large free form loaves, or 30 triplet tins. Possibly 80 buns, or 4 large pizzas. It can be used continuously like all my ovens. You don’t have to wait for the fire to become coal, you can use it and fire it at the same time.
Firebox infrastructure
The firebox
The firebox design incorporates a gasifier system which shoots hot air into the top of the firebox, causing the oven to burn its own smoke. The degree of gasification can be controlled by the top flue. The oven gets its air from underneath, but during lighting, the firebox is left half open to provide maximum air whilst establishing the fire. Airflow is governed down by closing the base bricks off, forcing the oven to gather air from underneath. This air is pre heated by a layer of stamped brick which warms up as the firebox is used. The oven can be converted to smoking mode by simply shutting down the outlet when hot coals have been established and loading up the firebox with aromatic twigs. The smoke can be made to be hot or cold according to your skill and taste.
The base of the oven is road grate, with heavy duty castors attached. Bricks are laid in channels on the bottom made of steel angle. The steel angle is also attached to the base for vertical framing, and will be tied in above the firebox and then at the top with more angle bolted on. Then I simply lay bricks between the framework. This ultimately makes the oven stronger, as the steel becomes an integral part of the masonry. It also makes the oven transportable.
The firebox itself has two rows of stamped bricks running up either side - these get very hot and provide hot air injection just under the baffle. This is how the oven gasifies. The firebox is lined with firebrick up both sides, which protects the stamped brick from the intense heat the bricks face.
Baking chamber with plates installed
The Baking Chamber
The baking chamber has heavy duty fins built into the brickwork to support the baking shelves or racks. They are positioned 2 brick rows apart, or approximately 160mm height. This is adequate for most sourdough or artisan breads - too much crown height means the base of the breads will cook too quickly - and the steel BBQ plates can be removed for tall baked goods or larger meats. The oven could potentially hold an entire small beast if customised. The BBQ plates could be replaced by racks, if the oven was to be used to create smoked meats or chickens, for example. The oven will also hold about 12 = 14 bread sized cast iron ‘dutch’ ovens as well.
So with that kind of capacity, the oven can cater for big numbers, which is very important from a business perspective. I’ve seen it hundreds of times , the new baker sets up their Rofco and gets a gig baking for their local market only to find they need a second Rofco pretty soon, creating a shackle for their back rather than a profitable business. Every time they grow, they need more equipment. I designed this oven to stretch it’s capacity from very small to quite large, as required.
The door was a story in itself
Hanging The Door
The thing that proved to be the biggest challenge for this build was the door. It is quite large and is effectively a quarter of the wall space of the baking chamber. I had to make it both light and heavy at the same time. It had to be light enough to be hinged from a masonry base but heavy enough to be able to provide some thermal mass. The frame is made from 1 inch steel tube, wrapped in thin galvanised sheet on one side. I had two attempts at getting the insulation right, as weight was a bigger issue than I expected it to be. In the end I used a sandwich construction of cardboard, perlcrete (perlite based concrete - very light), cardboard, cork tiles and finally timber. The framing of the door was made from hardwood fencing, which I had to carve down to reduce weight. Finally I’ve lacquered it with marine lacquer and linseed oil. It’s a sturdy finish, very tough. Inside, the galvanised sheet steel is coated with many coats of high temp paint. Nicely rustic which my client loves. Other finishes and materials can be used as required.
Hanging the door with piano hinge was a two bloke job, but luckily the other bloke was good at doors and came prepared with a door bladder!
Steel base plates for the piano hinge to be mounted on
It would take up too much space for this article, but the process of building steel plates onto the masonry in order to hang the door took a lot of hours and a lot of errors. I’ll just say that working with steel and masonry is never easy, and total destruction of the brickwork is a possible outcome if you happen to be unlucky. Happily, I was eventually able to get something really solid on, but it actually took two layers of steel and many repetitions of swearwords at great volume to make it work!
Using this multi layered system meant I could get cement nails through the steel and into masonry in parts, while in other places I could use heavy duty bolts. In the end there were about ten anchors in the masonry. The door holds on very well under load. It came in at just under 20 kg when finished.
So now it’s finished!
I hope this oven provides my client with many thousands of profitable and enjoyable hours of use as her business grows and unfolds. It presented me, as the builder, with lots of new challenges. Building this oven took me well out of my comfort zone many times. I’m a baker, not a bricklayer, carpenter, boilermaker or mason. But I had to get a grip on all of these things over three winter months in Gloucester NSW. Nothing is perfect on this oven - it’s flawed in every way - and yet it is quite a lovely thing. You kind of want to hug it.
My aim was to make a baking tool which operates on minimal fuel off grid using repurposed materials. My client asked for a wood fired oven which could bake a variety of loaves and other baked goods in a session. Both objectives should be achieved. The oven is also a smoker, which will, I believe, prove to be very handy.
While I blew my own time budget, I was able to keep the materials budget within 33%. In future commissions, I will have some better strategies thanks to the learning this oven has enabled. And my client now owns a very decent piece of kit which should never need replacing.
So what’s next?
I’ve designed quite a few ovens over the past 15 years, but I’ve only built maybe six or so from start to finish. Almost every build has turned into an epic tale, simply because they are hard on both the body and the brain. Once you get into building them, every bit of the build involves hard physical labour, muscles I didn’t know I still had, and challenges from a practical perspective which involve re doing things many times just to get them right. And lots of research. I never find a whole lot of good info online about what I want to do, EVER. So it’s largely trial and error. It’s for this reason that I’ll declare right now that I won’t be building too many more before I’m done. I’ve decided I’ll make my body and mind available for 6 more ovens, and that’s it. Six. No more, and it’s in writing here so you all know.
In building this oven I’ve also been able to create a matching design for a ‘white’ or ‘Indirect’ version of the same oven. It has a couple of extra layers of brick so it has a slightly larger footprint. It will have a similar if slightly larger capacity, and will have the added advantage of being able to burn waste materials for fuel, rather than only seasoned timber. The ‘white’ version will also have a number of refinements making it more suitable for virtually continuous use. Thus, it will b able to work all day long, every day , as required by shopfront bakeries and cafes.
If you would like to commission me to build one of these ovens, follow the button below. If you would like to discuss more about possibly having one of these built for you, my number is