Google+ Badge

The Dome - Part I

Making the brick dome for my oven was one of the scariest, yet rewarding, stages of the whole project – second perhaps to the first firing. For my dome I used old red clay solids (bricks), and followed fairly closely the method outlined by Russell Jeavons in his previously mentioned book.

Jeavons suggests you’ll need about 150 bricks, cut in half, to build a dome of this size. I think I needed closer to 200. I borrowed a big grinder with a diamond blade to cut the bricks. It was loud, tedious and dusty work, but the diamond blade cut through the bricks like butter. The only practical alternative to cutting the bricks is to use a brick bolster and a club hammer (Google it!).

As you’ll see here and in Part II, the dome is formed by laying one circular row of half bricks on top of another, slightly angling each successive layer up and in, to develop the curve. 

To assist this process, I fashioned a kind of cradle on an arm that pivots from the centre of the oven floor – this is used to hold the angled bricks in place until the mortar takes hold (only a few seconds) and to give you an idea of how each brick should be angled.

I made a pivot point out of any old rubbish – a bottle top and some unidentified scrap of plastic that seemed ideal for the job. 

I think the pictures of this technique, above and below, are fairly self-explanatory, but don’t hesitate to ask if you can’t make sense of how it’s supposed to work.

One last building note before I outline the actual building process…

I added some white builder’s lime (hydrated lime) to the mortar for the dome construction. The lime increases the plasticity, which helps the mortar to cope with the inevitable expansion and contraction the oven experiences as it heats up and cools down.

I used 1 part lime, 1 part cement, and 4 parts sand to make the mortar for the dome. Another good tip is to add a squirt of ordinary washing detergent to each barrow load of mortar – this gives it a lovely creamy texture that is super easy to work with. 

Now, to the building process…

To begin with, I half banged a nail into the centre of the oven floor, and, using some string and a yellow pencil, drew in the circumference of the first row of bricks. 

This helped me to see how every thing would sit – as with the base, I did a ‘dry run’ to make sure everything was going to work as planned...

Before starting on the dome proper, I constructed the archway that forms the opening of the oven. I had my local steelyard fashion me a semi-circular frame out of 4mm galvanised steel. This I secured to the oven floor with dynabolts, as pictured..

I must say, if I were to do this all again I’d probably use a temporary plywood frame, and build a self-supporting brick arch (as I did for the chimney arch). There’s nothing wrong with the steel frame, but it’s an additional cost and looks less elegant, in my view.

Any way, once you’ve sorted out some kind of opening for the oven, it’s time to start laying those bricks to form the dome! You can read about that and see the pictures in Part II…

No comments:

Post a Comment