I intend to post questions and answers to some of the most commonly asked questions raised by visitors to the blog. If you want to ask anything or suggest alternative answers please use the comments section below.
How is the ovens temperature controlled?
Temperature adjustment is very primitive. The oven reaches maximum temperature after about 3 hours of firing. I am waiting to buy a temperature gauge but have been told that the ovens ambient temperature can reach up to approximately 450 degrees C (and the brick floor even hotter). I know it gets hot enough to cook pizzas in 30 seconds (and singe the front of my hair off every time I fire it!). If I am cooking pizzas or bread then I keep a small fire burning in the back to keep the temperature up although it does drop after the initial firing (after an hour or so pizzas will take 1 to 1.5 minutes to cook!) If you wanted to cook meat it would scorch at these high temps so the best method is to scrape the embers out, wrap the meat in foil, pop in roasting tin then whack her in the oven. If you then block the chimney and door opening you can apparently leave it overnight (or for several hours) to slow cook as the oven temperature decreases. You would then probably finish it off by browning in a conventional oven, on a BBQ or firing up the clay oven again and popping the joint back in, uncovered for a few minutes.
What type of clay should I use?
I have had quite a few questions about the type of clay to use. As far as I know you can use any type of clay you can get your hands on. I dug my clay from a local farmer’s field here in Hampshire (clay overlying Upper Cretaceous chalk if you are geologically minded – maybe Paleogene?). The team at River Cottage get theirs from a pond on site, in Dorset (I think it is Blue Lias). If you can’t find any clay locally you could always buy potters clay which would be wonderfully homogeneous – free from large particulate matter. Which reminds me, try to get clay does not contain too many stones – they are liable to form the focus of cracks in your oven if left in the mixture.
Why is the plinth made of wood? Surely it will burn!
I chose to use wood for the plinth for two reasons. Firstly, I am really awful at building anything with bricks so the method I chose was easy for me. Secondly, the team at River Cottage HQ built their plinths using the same method and, if its good enough for them, its good enough for me.
In practice the plinth does not burn (much!). If you look at the building the plinth and oven base episode of my blog you will see that the fire (heat) does not come into contact with the wooden part of the plinth. The fire burns on the brick floor of the oven which is encased within the top of the wooden plinth box. The wood does char a little at the entrance to the oven but not so much that it will cause a major problem and you can always fix a heat proof tile there if you like.
At the end of the day its more of a practical (in terms of your construction skills) and aesthetic decision.
Is it possible to use a cement mixer to mix the clay/sand?
Unfortunately it seems the answer is not really! Lyndsey, a clayoven blog friend and fellow oven builder, recently tried the cement mixer technique but unfotunately it didn’t work. I liked his analogy which illustrates the problem:
“its very much like making pastry, with the clay being the ‘fat’ and the sand the ‘flour’.”
However, another blog visitor did get the cement mixer idea to work by firstly drying the clay, powdering it, adding it to sand in mixer then adding water. This to me seems like a rather long winded method though unless you have dried, powdered clay at hand!
I think you really do need to work the mixture and it seems puddling is the only way folks! I’d love someone to show me another way if there is one.
Where can I get clay from?
It seems that some of you are having problems sourcing clay. Ideally you will discover a free source. I managed to find a mound dumped in a local field by a local farmer but you’ll need to do some research and asking around in order to achieve this (luckily I have one of those freinds who can get hold of anhything!). Local garden centres might know where you can find clay because gardeners are obsessed with clay soils! Do you know of any local aggregate or brick making companies? Would the local council be able to help? Local geological societies or organisations? Geotechnical engineering companies? Construction firms (partic. ground workers)? Local architects? If you live near any ponds, brooks, rivers or streams you might find clay there but Of course it depends very much on your geographical location. If the local geology has been kind, you will find clay but some areas will be clay deficient. The UK has pretty extensive clay coverage due to it’s history of numerous iceages and marine transgressions (I knew my geology degree would come in handy one day!). Here is a website with lots of geological maps of the UK if you are that way inclined:
If you can’t find clay locally then you’ll have to buy some. One obvious source is potters clay. I have no expereince buying potters clay but please read this post from Nic, one of my blog vistors:
“I emailed a potters in fordingbridge, they said to me i needed a clay with a good amount of grog or molochite in, this helps give it strength for such a large item. They also suggest either P1480 Earthstone Handbuild clay or the P1484 Earthstone Crank clay (both have 20% coarse). The Handbuild clay starts at £11.39 per 12.5kg bag and the crank starts at £6.96 per 12.5 kg bag. Clay is sold on a sliding scale so the more you buy in one go the base price goes down. in another email to me they said it looks like a teracotta clay B103 grogged terracotta wold be good and I could use less sand as there is already 10% grog added to the clay, they think an oven the size of yours would take 3 or 4 12.5kg bags at a cost of £22.54. The shop http://www.briarwheels.co.uk are very impressed with your link and are telling people about it.”
PLEASE NOTE THIS POST FROM JOHN RE. VOLUMES:
“Just a follow on to Nic’s note above re buying clay. I have done so but the amounts mentioned will not build an oven your size. So far I’ve used 125kg of clay ie 10 bags and reckon for my last layer will need another 3 or 4 given what I have remaining. Best be realistic and forewarned.”
You can also purchase clay from here: http://www.angliaclaysupplies.co.uk.