Concrete base or not?

[jona45]

G'Day from a novice oven-builder in Australia! This is my first post on the forum- have been researching designs and decided to build a brick dome (as per FB). I have decided on an area in the yard- on ground that is retained by a wooden wall made from treated timber logs. The oven will be just above waist height. Plans describe a concrete base but I wonder whether a base of decomposed granite with sand on top is strong enough? I have wooden forms enclosing an area 1700 X 1300 for the oven.

Should the floor bricks be stable enough to hold up the oven?

I appreciate your advice.

Thanks
Jona45

[jengineer]

Re: Concrete base or not?

There have been a couple of builders that build into the "ground" The biggest thing to remeber is to insulate the oven from the stand. You don't want your fire heating up the floor and then heating up what is below it. Our motto is insulate, insulate, insulate.

How well is the wall made? Is it going to shift over time or is it stable. If you thing it is not going to move for 50 years or more then push on ahead with the plan. You are going to be putting on a small footprint a fairly large load. Most of the weight will be bearing downward very littel outward. As long as the retaining wall is stable you shoulkd be ok.

Finally it always helps to put in a few photoes so we can get an idea of the proposal.

toodle pip,

je

[nissanneill]

Re: Concrete base or not?

Hi Jona and welcome aboard.
Great to see more Aussies coming on board.
With your base,
don't make the hearth too low other wise you will be forever bending over to see to the rear of the oven. The cooking surface should be at a height that you can comfortably see everything in your oven, so the concrete floor should be at least 3" lower than your insulation top and that should be 3" lower than your brick hearth.
Always build your equipment to suit YOU, not anyone else! If you are tall, increase the height, if you are vertically challenged, then reduce thew height of the floor.
In his book on wood fired ovens, Russell Jeavons even suggests using an old metal galvanised iron tank, filled with sand and bottles to build an oven upon. Remember that your oven will weigh around a half a ton so the base and footings need to be fairly subtantial unles you plan on rebuiling when it settles and cracks up.

Neill

PS. What part of this wonderful country are you in?

[dmun]

Re: Concrete base or not?

I have decided on an area in the yard- on ground that is retained by a wooden wall made from treated timber logs. The oven will be just above waist height. Plans describe a concrete base but I wonder whether a base of decomposed granite with sand on top is strong enough?

It's been my experience that most wooden retaining walls, whether creosote (rail tie) or pressure treated, tend to rot out in about twenty years. When it does, the backfill behind the retaining wall will first sag, then push the remains of the wall away, and anything perched on top of it will be the worse for all that.

Am I correct that you are proposing to lay your insulation layer directly on top of the earth on top of the retaining wall? Domes have considerable outward force, and they move slightly with expansion and contraction. It seems that this would cause a dome collapse well before the lifespan of your retaining wall.

Make no mistake, building an oven is hard work, and you don't want to have a failure because you didn't take to build a solid, well supported base. There is nothing wrong with building on top of a wall, but the retaining wall should be as solid, and well drained, as the base for a freestanding oven.

[jona45]

Re: Concrete base or not?

Thanks for advice. I can see that the wooden retaining walls may not last 20yrs! I am re-considering this site.