Monday, 22 August 2011

Clay Oven Workshop

On Saturday, the group held a clay oven workshop at Gavin & Kims place which was well attended by members of the Melton Sustainable Living Group.  We had ten willing workers at our disposal, and we managed to occupy them all on various tasks during the day.

So from this:

To this in two hours (plus one day's drying and sand removal)!

So let me step you through what we did during the workshop.  However, be warned, there are lots of photos (click to enlarge).

Before everyone turned up at 10am, I received an order at 8am of 1 cubic metre of packing sand, which has a high clay content.  Kim and I had to shift this sand from the roadside to the area where we were making the oven.  It took me the good part of an hour to do this work alone.  After a cuppa and a biscuit, I made this template for the sand dome.  It is 50cm high and 85cm wide.

This picture shows how the sand dome was being formed.  Four people on a quadrant building up sand.

Here is the sand dome nearly finished.  You can just see part of the cardboard template.  Don't you just love the smiling helpers!

And from the front angle.  The sand dome just touched the front of the door arch.

Now that the sand dome was finished, it was time to get down and dirty.  We used a 50% packing sand and 50% clay mixture, and enough water to moisten it. There was quite a bit of aggregate pebbles in the sand as well, and a few handfuls of sugar cane mulch in the clay when we dug it out of the ground.  I didn't think it needed any more organic matter.

We started off with two stompers.....

Then there were four.  It became contagious.  It was great fun with everyone in gumboots (wellingtons to those in the UK) to stop their best shoes from getting caked in the stuff.

Then on to the table where a team of five helpers made clay logs that were about 6 cm wide and various lengths.

Then yet another team put the logs around the sand dome.  The dome was covered in wet newspaper so that it would make the sand easier to remove once the clay was touch dry.

The logs are placed like bricks to add rigidity to the form (well as best as can be).

Nearly at the top of the dome.  The dome at this stage was just at the edge of the door bricks.

This is the full height of the flue, just so you get a better idea.  

Once the dome was finished, we had to join it to the brick door arch.  More clay logs!

Then we started to smooth all of the cob logs.

Then we wet our hands and gave it a nice sheen.  We also filled any depressions in the clay dome.

As the sun was shining on the clay, we decided to coat it in wet newspaper to slow down the drying, to hopefully avoid some cracking.  This was the point that the workshop finished, and Kim served us a lunch of home made pizza to order, then dished up buffet style alfresco.  Everyone really enjoyed themselves, and a few people expressed interest at holding another clay oven working bee in about 6 months time.  I am certainly up for it, now that the design seams to work okay.  Thanks to everyone who turned up and lent a hand.

Anyway, yesterday some larger cracks started to appear, so I consulted my Back Yard Ovens Volume II book that I got from Earth Garden magazine, and it suggested that once the clay sets to a cheese like hardness then you should remove the sand.  The reason being is that the clay is trying to shrink, but the sand is getting in the way.  So out with the sand.

At one stage I had both shoulders jammed in the door arch trying to get the sand out! I wish someone had taken a picture of that.  The sand came out fairly easily once I had undercut the sand dome.  Most of it just collapsed and I just scooped it out with my arms.  The newspaper layer worked well.

I can't believe how big it is inside.  I estimate that with the hot coals pushed up around the edges, we will be able to cook 3 pizzas at a time, and afterwards about 4 loaves of bread.

So next steps are to move the sand that I left on the floor, light a small fire on every night for the next week to help the clay dry out, then on the weekend apply the glass wool insulation, chicken wire and clay/sand/cement render.

Pizza night at our place in about a months time to launch the oven?  What do you reckon team?


Eliza J said...

Hi There, I'm also planning a clay oven project with my dad. This oven looks great! I'm wondering can you help me with dimensions, or link to the plans?

Have you managed to fire it up yet? What is it's max temperature?

Looks great!

Gavin said...

Hi Eliza J,

You can find the full story of my clay oven over at The Greening of Gavin. Here is the link to the Clay Cob Oven series of posts.