Building a Brick Wood Oven

Why I built a brick wood oven
Building a brick oven had been an idea for a while to make wood fired cooking easy and more enjoyable. The oven requirements are simple needs to be - waterproof, insulated, closer to the house and have more use able space.

The clay oven melted in the rain which limited its use in the English weather, even with a make shift roof it still suffered in a few sudden down pours. This also meant cooking had to be governed by the weather so it did not get used in winter much. Simply put i wanted a brick built oven with a tiled roof to match the house, so it can be used in all weathers.

Insulation in the previous oven was non existent so once the fire went out the temperature dropped quickly. It did not have the temperature curve that would enable cooking more than two meals in it from one firing. So i wanted insulation on all sides and to the highest specification possible to give extended temperature range for longer.

Location of the clay oven seemed great at the time, it was in sunny weather at the end of a long garden as far as it could be from the house. The new ovens location is next to the garage on a hard standing that no longer gets used, which is 3 metres from the back door which leads into the kitchen.

The clay oven had an internal diameter of 80cm which may seem quite large and big enough for a couple of cooking trays in there at once. However due to it being a dome with a low centre the rake of the sides was very steep. This resulted in the usable space being probably more like 65cm.

Delivery day and storage

The delivery from Kiln Linings was over 1800Kg in weight split between two pallets. Fire bricks are very heavy (4.5 kilos per brick) so make sure you have good access or you are happy to put the work in moving them. The delivery was to the kerb only as expected, we also have a gravel drive so had to break each pallet down brick by brick and move it to temporary storage.

Storage of fire bricks was necessary as we were not going to use them straight away. They need to be kept dry as they will soak up rain/moisture and then you have to spend more time drying out the oven when its built.

The foundations and brick base was built by some builders, due to my time and skill limitations.

Insulation
The insulation is required to thermally isolate the oven itself from the base the oven is built on. There are many different insulation types but I used foam glass which is made from recycled glass. When using this you must wear eye protection and a face mask as the dust this creates is glass particles. The foam glass is the black slabs seen in the photo below. You also need gloves on, as this stuff can cut with just a a bit of pressure. I managed to knock a sheet over and tried to stop its fall using my legs, my shins were not happy after that incident. Foam glass does have a high insulation value and is made to build on top of, so it is good for this project. It does start to soften over 600°C, but I cannot see that being a problem.

Floor layout was completed with bricks on their sides so the oven has a larger thermal mass than if the bricks are laid on the other face. As we want to store as much heat as possible for long slow cooking. The bricks are laid dry with no screed bed or fire cement used.

Temperature Measurement
Fitted K type thermocouples which can measure up to 650°C - below the bricks in between the insulation and the bricks to ensure that the fire bricks are full saturated with heat. There is also a thermocouple in between the bricks just below floor level. So when these two read the same temperature the floor is fully saturated with heat.

The back wall of the oven was built after several dry runs of the full length of the floor being laid. As its not like it can be moved anywhere after its been built. The first arch was then built using a template for temporary support and as guide for the height of the arch. Kiln Linings do arch kits so all of the bricks are tapered as required to make an arch. This saves time cutting multiple bricks which would require a good saw and blade as fire bricks are very dense and hard to cut. However you can just use a hammer and chisel to cut fire bricks to length if you take your time.

The fire cement we used to bond the bricks together is premixed, air setting type but has a requirement that joins should be between 2mm and 5mm thick. After finding some advice on its use online I used a tile adhesive spreader which worked well at keeping the gaps between bricks uniform. The fire cement air sets to some degree, but does not fully set until the oven is used to above 300°C.

After a few problems and a change of support the first arch was completed. It is far from perfect but pleased with it. Notice at the bottom of the arch there is two standard fire bricks to create a higher arch than that the arch alone would be.

The last arch going up on the second day of the oven build. I put a lot of the white plastic down to keep the oven floor as clean as possible. The fire cement sets hard on the fire bricks and is hard to clean off later, so best not to get it on there in the first place.

At some point you have to just get in there and clean the inside of the arch and point any gaps you missed.

The oven was based on four arches to give a nice large cooking area. the arches are 230mm deep so that gives a 920mm depth to main oven cooking area. Width of the oven internally is 710mm, so its wide enough to get two standard cooking trays in side by side. Because of the depth you can also have different cooking temperature 'zones' from the fire on the back wall through to the door way which is yet to be built. The arches are not perfect but they are all standing and it looks more like a proper wood fired oven.

Now the front of the oven needs to be closed off to create a proper entrance and a chimney separate from the main oven body. The height of the door way needs to be 65% approx of the height of the arch inside the main oven body. This creates the best heat retention in the oven, not letting the flames and heat spill straight out of the front of the oven. While also allowing oxygen to be drawn in at the correct rate to feed the fire. This also means the unburnt gases that come out of the wood do not go straight up the chimney but are retained and burnt creating more heat in the oven.
I used 50x50x5mm stainless steel angle iron to bridge the gaps across the door and entrance opening bought from ebay.

The front of the oven is now closed off and the opening to the oven and chimney needs to be completed.

From the outside you can now see the length of the oven including the entrance and the start of the chimney.

A bit of light warming to help it dry out slowly. You can see where not all of the arches meet up inside.

The ceramic fibre blanket is now wrapped around the oven before the outer insulation can be added. The ceramic fibre blanket can with stand very high temperatures 1200°C so this is used as the first layer of insulation against the fire bricks. Chicken wire is used to hold the fibre blanket against the oven.

More foam glass is used as the outer insulation to the oven, held together and gaps are filled using high temperature expanding foam. Its not very pretty looking but its more about a continuous layer of insulation around the complete outside to create efficient use of the heat stored in the fire bricks of the oven. Its going to be covered when its complete so all this will be hidden from view.

The last layer of insulation is almost complete with all gaps filled in with expanding foam. The excess foam will be removed after it has dried.

The builders came back on site and finished the rest of the brick outer shell for the oven including the oven. Half a brick has been left out to gain access to the thermocouples for a later project.