I'd spent quite a while researching DIY ovens and the internet is jam-packed with details of many. But none was quite what I wanted. I knew I didn't want to build one in clay as these seem to crack and weather quite quickly and really needed some sort of roof for protection. I wasn't too keen on any construction that needed lots of bricks and formed arches as I knew the limits of my ability. In the end, I decided to cast a dome out of fire-proof concrete. Not the cheapest of materials but not overtly expensive.
Was it worth doing? Yes. Would I do it the same way again? Yes.
Given the weight that the final structure was going to be, it needed a substantial base to sit on. After putting in and levelling some shuttering for the sides, it was a good place to lose some old hardcore we had lying around.
It was all tamped down with a great big sledge hammer to consolidate well.
The slab was made from a concrete mix (oh, how I love mixing concrete by hand) and was probably about 4 inches thick. I put this around the side of our house, so that it was out of sight (it is a big beast) and the opening was well away from the direction of the wind.
On top of this I built a frame with breeze blocks. I can't remember the exact dimensions but the size was based on block size: two blocks long for the sides and three blocks high. I wanted to avoid cutting blocks unnecessarily.
Block laying is not my strong point but, according to my spirit levels, it didn't turn out too badly.
I faced the block frame with standard bricks. As each block was two bricks high, it was easy to build up to the top level of the blocks.
To allow for what was going to be the base of the oven, I put another course of bricks on top of the others. I also built a central pillar with more blocks and this would give some additional support to the base.
The first of the oven base layers was a piece of external plywood, probably 2.5 cm thick. The weight of the oven would be taken up by the 'walls' of the frame so I thought this thickness would be adequate.
Next was a 2.5cm layer of the ceramic insulating mat. Hopefully this would help insulate the plywood from the heat.
What I should have as the base of the oven was not a decision I took easily. I was leaning towards tiles of some sort but, a conversation with someone at a kiln supplies company (Castree Kilns), made up my mind for me and I went for a ceramic batt (base) and set that in 5 cm of insulating refractory cement. Was all this base thick enough for the job? All I can say is that it's been in use for about 9 years and hasn't collapsed yet!
The finished oven will be large enough for bears of varying sizes.
There must have been a reason for my taking these bear photographs but I can't for the life of me remember what it was. Maybe they were part of a 'what am I building' quiz I set some friends in North Carolina?
And this image falls into the same category. Why have I got a wicker (willow) basket on my head and, apart from it being rather stylish head wear, what am I really going to use it for?
Pizza ovens are domed shaped and the question was "how to get this shape? Some people use mounds of sand as a shaper but that struck me as both messy and crude. The alternative I came up with was getting a cheap wicker dome, shaping the oven around this and then burning it out. By chance I was put in touch with a lovely wicker 'artist' who lived on the edge of Bodmin Moor (Carol Horsington of Cornish Willow at Treovis Cross Farm) and she agreed to weave what I needed to my exact dimensions. I think Carol was rather intrigued by the challenge!
Slapping concrete directly onto the dome would result in a lot of it falling through the strands. To prevent this, I wrapped it in paper masking tape.
And here is the finished article in place, centralised over the ceramic batt on the floor of the oven.
The oven needs a door and I got our local blacksmith, Michael Broome, to make me a frame in steel. The width of the steel was 8 inches, which was intended to be the finished thickness of the walls. The width of the opening was about 1 foot, which I reckoned was wide enough to accommodate the largest size pizza I would make. If you want to really get into the intricacies of oven design, you'll soon learn that there are certain ratios between inner oven diameter, inner oven height and oven door height that the experts say you need to have. The most important here, and the only one I used, was that the oven opening height had to be 63% of the inner dome height. The height of the steel frame was based on this calculation.
At the outset I had to decide whether to have a chimney or not and I decided against it. The main advantage of a chimney seems to be to take the smoke out of your face when you are cooking, but if you get the dimensions right (see above), this shouldn't be a problem. The main disadvantage with a simple chimney design, and I certainly didn't want anything complicated, is that lots of heat will go out the chimney instead of heating up the oven. I could live with anything that didn't add any complexity to my design. After many uses, smoke 'blow-back' has never been a problem but I did put a clay chimney pot on top for cosmetic reasons, and because two friends (John and Rosie) had one going spare.
I fixed the door in place with some more masking tape. The tape around the sides indicated to depth of each layer I would be putting on. I was aiming for an overall thickness of 8 inches.
The first layer was of dense castable concrete (from Castree Kilns). This is material designed for hot-facing lining of kilns, forges and furnaces and was suitable for temperatures up to 1400C - more than adequate for a wood-burning oven. It came in 25kg bags and was mixed with water to get it to the right consistency.
There was a lot of trial and error in getting the cement to the right consistency. Initially, I had intended to trowel it on but, in the end, putting it on by hand (suitably gloved) worked out best. If the mixture was too wet, it slumped (crept downwards). It was like making a giant mud pie.
Once the first layer was on and dried for 24 hours, I cut through the wicker liner and got ready to burn it out.
My photographic record is incomplete but over the first layer, I put some of the ceramic insulating blanket, held in place with chicken wire. And over this came an approximately 10 cm layer of insulating castable concrete. The rational of the layering was as follows: the dense castable takes up the heat and the insulating ceramic blanket and insulating castable minimises heat loss. It seems to work as, in practice, even after a long burning, the outside does not get unbearably hot.
The finished oven with the liner burned out and the chimney pot perched on the top for effect. I didn't cement it on for a while. As a rough estimate, I'd say that the oven had a metric tonne of material in it and will withstand a nuclear blast. There have been a few cracks over the years but nothing serious and these have been easily repaired by using heat-proof mortar.
To give it a vaguely Tuscan ambience, I painted the outside with masonry paint to give it some protection from the elements. It doesn't get hot enough for it to burn off and, every now and again, I slap another coat on to freshen it up.
The oven in action. A couple of things of note here. To the right is the door I made from a piece of thick oak I had lying around. I'll probably replace this with something else in the near future. At the back of the oven is a semi-circular fire grill and I use this to push ashes to the back of the oven to allow me room to cook the pizzas.
And this is my homemade wooden 'peel'. Dusted liberally with semolina before putting the raw pizza on, they work a treat for getting things into and out of the oven. It takes about 90 minutes or so (and a lot of wood), to get it up to temperature which I guess is in excess of 400C, and pizzas take about 5 minutes to cook at this temperature. Long oven gauntlets are a must when cooking, unless you don't mind the hairs on your arms being singed.
 |
| Here is a time-lapse video of the above slides. I can't remember how long it took to build but it was a fun project. |
No comments:
Post a Comment