Comments on: 11. Clay Clay Clay!

By: Simon

Simon — Thu, 24 Sep 2009 13:15:04 +0000

Thanks for the input David. My thoughts:
(1) yes I have seen paving slabs used so go ahead. Not sure how the production of concrete compares to the production of bricks in terms of their respective environmental impacts.
(2) Grogging, which for those who don’t know, is the process of adding small particles of fired clay to wet clay – normally for pottery making purposes. If you are buying clay from a pottery suppliers you DO NOT need to buy grogged clay. As David infers, we add sand to the mix anyway and the oven walls are never “fired” as such so the grogg has no effect whatsoever.
(3) Again I have seen ovens with mosaic patterned outer layers. The thing to remember though is that these ovens do crack and, as a result, you might find that your tiles end-up falling off. Worth a try though!
(4) You need an entrance for air to get in and a different one for air to escape otherwise your fire will go out!
(5) An air vent at the back would be fine.
(6) Vermiculite seems like a sensible idea.

All the best

Simon

By: David

David — Wed, 23 Sep 2009 14:46:21 +0000

Several points

(1) A big concrete paving slab seems an easier way to make the oven base. Probably no more environmentally nasty than commercial clay bricks.
(2) If you advise adding sand, is there any point in paying (a little) extra for the grogging in the clay?
(3) If you want to make the outer surface more resilient to weather, why not use mosaic tiles – perhaps broken fragments of tiles or purpose made mosaics? This would give a largely glazed outside, and might only need repointing to stay water resistant. You might have to wait until the oven had been fired a couple of times to allow the rest of the clay to dry.
(4) The oven we saw at the Henham Steam Fair (cooking pizzas for the visitors) did not have a chimney – is the chimney really necessary?
(5) If you do need the chimney, then why not also an air vent at the back to help get the oven fired up? It could then be blocked off during normal cooking.
(6) How about using non-inflamable insulation (such as vermiculite – made from rocks) in the insulation layer to avoid the problems with the wood chips catching fire?

Cheers

David

By: Simon

Simon — Tue, 22 Sep 2009 11:34:07 +0000

Hi Danny I doubt it would work. Pottery kilns reach temperatures well in excess of 1000 degrees C. I’m no expert though so by all means give it a go and let us know.

Cheers

Simon

By: danny

danny — Tue, 22 Sep 2009 11:27:56 +0000

cheers simon ,one more tought could you fire the outside with a fire torch to give that pottery glazed look or would this still not be hot enough?

By: Simon

Simon — Mon, 21 Sep 2009 09:14:39 +0000

Hi Derek. You can of course use concrete, cement, brick or any other materials to make an oven. My main choice for using the clay/sand mix is an environmental one. The cement industry is globally responsible for pumping out vast quantities of CO2 (over 5% of global totals – http://www.guardian.co.uk/environment/2007/oct/12/climatechange). As for glass fibre – I believe it is a carcinogen and no doubt also has questionable manufacture processes associated with it (pollution etc).

Ovens like mine have been built using the same materials and techniques for millennia and, yes they do crack and eventually fall apart, but one can always build another one – that’s part of the fun!.

Cheers

Simon

By: Derek

Derek — Fri, 18 Sep 2009 16:29:15 +0000

Please dont shout – but if the clay is prone to cracking could it not be substituted with a fibre reinforced concrete mix? – I’d have thought it would have the same heat retention proprties and if made with two layers you could use a glass fibre insulating layer sandwich between …

glad to hear other vies or thoughts

By: Simon

Simon — Thu, 17 Sep 2009 07:56:55 +0000

I can’t think of anything that would be suitable Danny. A glaze, in the traditional pottery sense of the word, would not work because the outside of the oven never reaches a high enough temperature. I have seen ovens with a white finish which could be lime mortar. I prefer the au naturel look though personally.

Cheers

Simon

By: danny

danny — Wed, 16 Sep 2009 15:21:17 +0000

can you glaze over the final layer ,would this strenghten the oven? would it minimise cracks?or the opposite.if so what kind of glaze?

By: Simon

Simon — Wed, 10 Jun 2009 06:40:01 +0000

I love the blog and I love the oven Simon – brilliant! I have been thinking about building a portable version too recently so I will be watching the final installments of your blog with interest. I’ll also take you up on the offer of a pint when I’m next in Sydney!

Great work!

Simon

By: Simon M

Simon M — Wed, 10 Jun 2009 05:08:49 +0000

Hi Simon, thanks for the blog, a great resource you’ve created here – the oven looks superb and I love the way that you’ve stuck largely with organic materials.
I’ve been working on a portable contraption for the back garden in Sydney – still a week or two away from completion but can’t wait to fire it up for real.
Check it out if you have a chance, would appreciate your feedback.
All the best