Sunday Volunteers 18 Nov – Cob Oven stage 2

What a great turnout of people and weather for todays activities! Nice to see a few new people wander through too.

Today we rebuilt the main structure of the clay/cob oven on the base that had been prepared last week. The mortar had settled and is drying out and setting well under the bricks and todays clay mix was basically the same but included grass clippings to add texture and structural reinforcement to it for the main oven arch and firebox with the chimney built into the top. We are using a very standard traditional cob/adobe/clay oven building process and design.

So first we discussed the build process and mapped the structure out and created a giant sand castle for the interior space that included the entry tunnel to reduce overall work.

The height of the firebox arch and door was set to be the usual 63% of the internal oven height. We used templates for this cut from ply wood which makes the job much easier. (also many hands make it faster work!)

Then we covered that sand structure in wet newspaper and slopped on a thin gooey layer of clay slip (clay and water mixed to a sticky fluid state) to help create a good smoothinternal surface for the oven.

After a short break to let that dry and have tea and scones we started in on mixing the main clay/cob batches. This was the usual recipe of 2 sand to 1 powdered clay with the added grass clippings to add texture.

This mixing process was perfected by the group of tree huggers we had stomping (or more technically – puddling) the clay mix into shape. Fantastic job done there!

At this stage we added some trimmed pots to the top of the entry way arch to act as the chimney. One smaller pot was placed inside the other larger 20cm one to create a small lip at the bottom of the chimney to rest any future metal tube chimney stack on etc.

Then we started the wall build and worked our way up and over the sand structure pressing it all in carefully to avoid air bubbles and joins etc where it could shrink and crack etc. The mix worked very well and although it was slightly on the damper side it was easy to blend and smooth out. We placed some bricks around the edges to help stop slumping of the walls while it dried more.

Then we all gave it a nice rub and a hug to smooth it all out and left for the day happy. 🙂

Next week we will be laying another external layer of clay mix, cleaning up bumps and surface defects and then decorating it. We will also clean up and render the surrounding rough brick edges etc.

If the main structure is dry and strong enough by next Sunday session we will be extracting some of the sand and lighting a small fire inside and slowly drying it out from the inside and maybe even get it dried out enough to cook.

A big thanks to all those who came today and helped and contributed to the event! 🙂


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