Hendo's Oven

[Hendo]

Time to start posting some photo?s of my brick oven construction. I originally proposed to build a stand-alone unit, complete with gabled tiled roof, like so many I have seen in Italian backyards. But before I knew it, the project had increased to building an adjoining gazebo, and then still more to incorporate an outdoor kitchen, complete with sink, bar fridge, barbecue and deep fryer.

The first photo gives a perspective of the construction site, with excavations for the oven & bench footings and trench for gas & water supplies and storm water pipes already completed. The area next to the back fence has been levelled for the gazebo and aggregate dumped for the slate paving. The mess has truly begun!



The next two photo?s show details of the footing excavations. I opted to go for the same footings as specified for our house extensions some years back, as they will have to support a similar weight in our highly reactive clay soil. Probably overkill, but time will tell. The main footing is 14? wide by 36? deep, and reinforcement is by 6 ⅝? bars (3 top 3 bottom).

[Hendo]

Re: Hendo's Oven

The excavations lined with plastic membrane, and formwork and reinforcing steel mostly installed. Unfortunately, due to the slope of the land, the footing was stepped down by three brick courses (10?) from the oven slab to the gazebo floor, effectively lowering the hearth slab on the uphill side by the same amount. Less height to store wood for the fire ? darn! I was really depending on 4 block courses to enable good access for the wood storage area under the hearth slab.





The cavernous excavations took over 6 yards of concrete to fill! And of course it started raining half-way through.

[Hendo]

Re: Hendo's Oven

Oven slab and beam floated off, and looking a bit on the wet side, due to the rain.





Next day, the formwork was removed ?

[Hendo]

Re: Hendo's Oven

? and the rubble for the pavers spread and compacted. Holes were dug for the gazebo posts.





Gazebo structural elements installed, and a 1? copper gas line for the barbecue laid in a trench dug around the oven slab.

[Hendo]

Re: Hendo's Oven

Electric cables installed and pavers laid, together with corrugated steel roof & guttering, and blue board cement sheet fixed to the structural stud-work next to the fence. Apart from some lattice and a textured surface applied to the blue board, the gazebo structure is largely finished.



Now on with the hearth stand! The footprint of the concrete support blocks is marked out ?



and the first course mortared in place.

[Hendo]

Re: Hendo's Oven

The blocks are designed to interlock with adjacent blocks and the course above, so once the first course has been laid in mortar (to compensate for any unevenness in the slab), the remaining courses are dry laid. Mortar thickness varied from ?? at one corner to a little over ?? at the opposite corner, so the slab was reasonably level. The blocks are 8? high and are bevelled on the sides and top, to simulate a ?? mortar joint. Laying these blocks was very satisfying work, as it all goes up so quickly!





Midway through construction of the hearth stand, I decided to use ribbed steel decking, instead of the usual plywood formwork, to support the hearth slab. This is used extensively in the building industry for multi-story buildings, and supports the concrete slab - both physically and structurally. I used 1mm thick galvanised steel, which is able to span over 2 metres (6? 6?) in a single span for the 5? slab thickness that I ended up with (my span is less than 4?).

At around the same time, I decided to change from 4? vermiculite concrete to 2? Calcium Silicate boards for my sub-dome insulation layer, with the result that I could increase the height of my hearth slab to accommodate more wood, and make it a bit easier to retrieve. The down side was that each block of the top course of concrete blocks had to be cut to 3? high. I achieved this by way of a diamond blade in my 5? angle grinder, and it was fairly straight forward, if a bit dusty! The internal webs of the blocks were drilled as much as I could from each end, then the block split quite easily. In this way, I successfully managed to get two ⅜-height blocks out of each whole block. I made sure that the overall height of the blocks was the same as a whole number of brick courses, because the steel decking for the vent landing would be supported by brickwork at the oven entrance ? part of the brick bench structure in the gazebo.

[Hendo]

Re: Hendo's Oven

I also put in some U-shaped ?? rebar down four of the cores and across the top of the steel decking, and held these in place with some scrap timber pieces while the cores were being filled. I had a mate help me with filling the cores, and we rodded each core thoroughly (with ?? rebar with a bullet-shaped tip) after filling with ready-mix concrete. I ensured that the cores were thoroughly moist before filling with concrete, but even so, the blocks sucked a huge amount of moisture out of the concrete and rodding was difficult.

[Hendo]

Re: Hendo's Oven

Then, on to the brickwork for the bench. After the walls were marked out, the bricklayer got laying! In a few hours, he had finished all the brickwork needed to put in the last piece of steel decking and construct the formwork for the hearth slab. The brick walls will both support the bench top and act as dividers between (from left) the sink cupboard, bar fridge, ash pit, barbecue/wood storage and deep fryer with cupboard below.

[Hendo]

Re: Hendo's Oven

Another afterthought, motivated by other members’ experiences was to install some thermocouples to measure hearth temperature, both near the surface of the cooking floor, and at the junction between the floor and sub-dome insulation layer. As I could obtain only a six way selector switch for the digital temperature display, I opted to put four of the thermocouples in the cooking floor, and two in the dome. I wanted to ensure I could replace a thermocouple with a minimum of fuss (if I ever needed to), so I decided to make up some thermocouple housings which could be fixed to the steel decking. An instrument supply company provided 4 thermowells which had been made to the desired length, and I fixed these to cheap stainless steel mugs via a brass bush and back nut.



The ⅛" diameter thermocouple probes will be fastened inside each thermowell by means of a ¼" compression fitting, accessible from under the slab.

[Hendo]

Re: Hendo's Oven

The completed assemblies were then fixed in position with silicon sealant to the steel decking which had had 3? holes cut through it with a hole saw. Each assembly was connected to metal conduits (old ?? water pipe) with silicon, after a draw wire had been threaded through the pipes. These days, galvanised water pipe is unheard of in the plumbing industry, so I had a devil of a time trying to find a pipe threader to connect all the fittings! All the pipes terminate at a convenient height above the future bench top where the switch and temperature display will be mounted in a brick wall.

[Hendo]

Re: Hendo's Oven

By this time, I had also placed some 8? weldmesh (I ordered ?? but was supplied with ⅜?) and had started to box up the hearth slab area with old facia and barge boards ? cast-offs from the adjoining shed. Note the small blocks screwed to the ends of the timber forms on each side of the hearth slab [OP]. These enable the screws which secure the assembly to be fastened into cross-grained timber in all instances, rather than into the end-grain of the adjacent timber form. A much stronger joint results, and eliminates the need for strapping to keep everything together. I first noticed this on VillaGok brick oven - May 2005 which is also where I got the idea to build the hearth slab on a separate structure, and enclose the lot in a brick veneer. An interesting site and worth a look.

I was advised by my builder to attach the ?legs? of the frame to the outside face of the timber planks, rather than underneath. As a result, it was very easy to adjust the height of the formwork, prior to fastening the legs.

The day the hearth slab was to be poured had come, requiring some last minute rebar around the formwork for the ash slot. I would have preferred a single U-shaped piece of rebar, but I think this will do the job, considering the steel decking underneath.

[CanuckJim]

Re: Hendo's Oven

Hendo,

Congratulations on both a fine, well planned project and a fine photo essay. This will be a monument to your determination. Keep up with the pics. Very cool indeed. Just wait till the cooking starts.

Jim

[Hendo]

Re: Hendo's Oven

Wires had been threaded through the timber forms from one side to the other, and tensioned to prevent the formwork from bowing out during the concrete pour. These obviate the need to brace the centre of the forms with angled props. A very simple way to ensure that all formwork stays put! In the next photo (and others), you may be able to make out two angled wires running from left to right, tensioned with short lengths of rebar, and one twisted one going from top to bottom ? where a small metal plate prevented it from cutting in to the timber form. I had also drilled the timber forms on either side and threaded some brick ties through, which will help support the external brick veneer.



I also decided at the last minute to run some PVC plastic tubing through the slab, to provide for copper pipes for water and gas, should I ever decide that I need them on the opposite side of the oven to their supply point. The alternative would be to dig a trench around the oven footing again, which I?d prefer not to do. They may never be needed, but they?re there if I want them, providing they don?t melt in the meanwhile!



All is now ready for the concrete pour. Ready-mix concrete again, as it proved to be cheaper than buying bags and mixing it myself, and so much easier! It took the delivery driver a while to work out what was being made, but he got it eventually. In the driest state in the driest continent on earth, most people building such structures are doing it for rainwater tanks, and this is usually the first guess. However, brick ovens are now being built in ever increasing numbers.

[Hendo]

Re: Hendo's Oven

After the pour, with which I was again assisted by a good mate. It was fast work, as the temperature was getting into the thirsty thirties (or in the eighties on the Fahrenheit scale), so there was frenzied shovelling, rodding, screeding and tamping, and no time for ?in-progress? photo?s unfortunately. Finally all was complete.







Next ? on to the dome!

[nissanneill]

Re: Hendo's Oven

Great detail Hendo.
I'm pretty thorough with most things that I do but you have certainly exceeded my expectations. The brick oven is only a part, although it be the catalyst for a major project. In a way, I am in a similar situation Also in Adelaide where I am to put an oven into an existing entertainment area which will then be upgraded to meet the new needs. I have another project to complete first and a daughters wedding before I commence the oven but the planning is well underway.
I will follow your progress with envy and maybe get some more ideas.
Thank you for your pictures.

Neill