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Karls 05-10-2012 05:01 AM

oven floor
This is my first post and am new to the forum and wood burning ovens. Ive recently built a 36 inch , which i built from this site . My goal was to build it with local products (on budget). I live in South Africa. I have 50 mm vermiculite under a 60mm clay paver. The dome is built with solid old clay bricks and ive used a crusher cement mix for the mortar(given to me by a local who assured me is fire proof). The dome is covered with a 25mm blanket and about 80mm of vermiculite. Ive then plastered a waterproof plaster over.

My problem is the floor doesnt get hot enough for pizza. With a big fire the dome gets over 950f and the cooking floor max at about 550f even with the flames lapping over. After 1 or 2 pizza it drops quickly.

Do u think the clay floor is the problem or has anyone got any sugestions?
Does the oven get hotter with age?

Lburou 05-10-2012 10:08 PM

Welcome :)
How many fires have you had that brought the dome temperature to 950 F?

Many times, the oven floor does not get up to pizza temperature because of trapped moisture (in the floor and vermicrete). You could see the oven floor get hotter with each firing, your insulation sounds about right. :)

Les 05-10-2012 10:39 PM

Re: oven floor

Your build sounds spot on. The question is how long is the fire? After a couple of hours the hearth should be pretty damn hot - not 550f. Has the dome got hot enough to clear the soot? Even in a perfect world, you need the floor to re-charge if you are cooking many pizza's.

Karls 05-11-2012 03:46 AM

Re: oven floor
The oven has been fired about 6 times to clear the soot.Maybe you right it needs to get the moisture out.Im taking measurements after the oven has been heating for about 1hr.

I normally make a big fire in middle then move it across to the side and more wood and have flames lapping over the dome.Then i take the temp. Hopefully im doing it right?

david s 05-11-2012 06:33 AM

Re: oven floor
Don't know how many fires you've had in it, but I think Lee is spot on, it sounds like your oven still has moisture under the floor. If you covered the vermicrete insulation under the floor as soon as it set, then you trap a huge amount of water under there (about a third of the total volume is water) and it's then hard to eliminate. I think it's best to leave it to the sun and wind for a couple of weeks (if possible) to do most of the job of eliminating the water. It takes many more fires than you would think to dry an oven out properly. My guess is that you will find the oven improves if you just keep firing it. Try this before you do anything drastic.
50mm vermicrete on its own is a bit thin IMO what ratio of cement did you use? And did you add any sand to the mix. These will both reduce the value of the insulation.

Karls 05-14-2012 04:04 AM

Re: oven floor
I used 1bag of vermiculite to half a bag cement(50kg bag)>There was no sand added.

david s 05-14-2012 04:46 AM

Re: oven floor
Assuming the vermiculite is 100 litres then your mix is around 5:1 by volume. I think the normal requirement is around 100mm under floor insulation of 5:1 vermicrete. I still think you have moisture under there and the performance will improve with more firings.

Neil2 05-15-2012 10:15 AM

Re: oven floor
"I normally make a big fire in middle then move it across to the side"

Try leaving your fire in the middle until the wood burns down to coals and you are ready to cook. Then push it to the side or to the back.

Neil2 05-22-2012 08:19 AM

Re: oven floor
When I first started using wood fired ovens, I would push the coals to the side. Now I push them to the back. I find this seems to free up more cooking space and gives an element of heat control with the hotter area towards the fire and cooler towards the opening.

I generally find I can do all the cooking with the heat from the initial firing and do not add wood.

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