Re: Hardening of Outdoor Oven clay?

Posted by Rado (203.164.249.69)

In Reply to: Re: Hardening of Outdoor Oven clay? posted by Robert Richard

Hi Robert,
A bit on work with and drying the clay from my perspective; find lighter in color clay deposit (whitish, pinkish, creamish.) You can do test by forming 1" - 2.5cm in diameter ball, leave it to dry, when dry it should hold and be hard although still finger nail can mark it. I would choose to mix sand into the clay (remember the coarse clay body?) and would add very little water amount as wetter the clay higher the shrinkage rate. Also I would go for adobe making for the hot face, as mentioned before for better clay oven quality, and would start to put them together when semi dry. Drying: from soft consistency the clay hardens and at this time clay attracts highest shrinking. Clay becomes hard but still cold on touch and dark, the same as when it was soft (reaching this point when using no adobes, wise would be to cover the soft structure so drying speed in edges is even with the center.) Then spots will start to appear where the drying progresses faster, these spots become lightish in color. At first lighter spots are still cold on touch. The whole oven will change from the dark to lighter color and the slower it takes for this change to happen the better for smoother clay job. At this stage the inside is still too wet, you can feel it when touching with hand the walls will feel water cold even though the color is lighter. Leave it for a week and start with very little fires, such as which will not heat up walls into water boiling temperature, drying fire should be small producing short term heat that will start to soak through structure, fires should increase gradually. Well, all this above is from my own experience ... if you could write in more on what you have hear from old builders on drying process of those 3-4 weeks.

Thanks for the link, great to see people participating on such workshops. Often these ovens are built for gaining experience from building and of course it can never end without good fun from firing, pizza making or bread baking, having limited time for all of this and after the evens are dissembled. Look at 3rd last profile close up photo after Norbert made cuts in the clay, which is perfect test/example showing shrinking on inside hot face.
If you found some other links interesting mention it.

Re: Hardening of Outdoor Oven clay?