Building outdoors on ground in tropics

[mk e]

It looks a fine plan. I'd add to use an acrylic product or addative in the top coat or maybe paint it.

I use plain cheap mortar under the fire brick.....others scolded me.... I've seen it done without issue many times but high temp is a safe bet if there is doudt in your mind.

[UtahBeehiver]

You have a great resource in Townsville south of you. David S is our casting expert and one of our old time contributors to the forum. He can give you some guidance on your project, material resources, etc. You can PM or he may see your post. An unenclosed oven is more prone to water issues but there are plenty of builds done this way. IMHO, some type of waterproof render will be needed over the 100 mm vcrete dome insulation, you could make the ratio higher up to 10 to 1 for better insulation qualities. No more than your proposed 6 to 1 on the floor.I am not sure what load the cement sheet can handle with the tube spacing but these ovens can get quite heavy. Being recessed, the oven will be exposed to water so sloping of the floor will be critical. Floor height rule of thumb is elbow height. There are a few builds similar to yours where they have build ovens into slopes or recesses.


Update
I reread you narrative and I see you proposed tiles or render on the outer coat which were not on the sketch I saw. I know that David S suggest a 100% water down acrylic coating over render for water proofing.

[Johnnycantplaytoday]

Hi All,

Newbie here - Just chasing some advice / feedback on my Outdoor In/On Ground Pizza Oven plans before I start building. Started out just wanting to build a simple cheap vermicrete dome over a sandcastle with no insulation to make some Friday night pizza's to go with my cold beer. But after lots of homework and many sleepless nights my build plans have taken on a life of their own.

So to my situation. The only available practical place to build near the house is on the ground behind a concrete rock wall about a metre high. See below photo. This is out in the open and as we live in the tropics, it would be subjected to weeks of heavy rain at a time, not to mention it's in the garden and would cop additional water from hosing. Not really practical to build a roof over it and it wouldn't suit the immediate surrounds.

My concerns were none until I started reading all the posts on this forum about moisture, curing, cracking, lack of heat retention, homebrew etc etc. Didn't come across too much info on building in the ground tho.

So after many beers of thought, my plan is to excavate about 300mm into the ground behind the top of the wall. Form a 100mm thick slab with about a 250mm deep, 1200mm-1300mm square "recess" for the oven base with drain holes to the front of the retaining wall. Oven would be approx 850mm-900mm Int dia) On the concrete slab in the recess will be some 25x25mm aluminium tube to mount a 20mm Fibre Cement Sheet to above the concrete floor. On this sheeting I was going to form a 100mm vermicrete slab (6:1) for insulation, then on that pour a 50mm Refractory concrete slab for additional heat retention. Then on that would be the 35mm thick Fire Brick oven floor (same height as top of retaining wall). There would be approx 100mm perimeter around the oven in the recess to keep moisture and water away from the build which would all be covered over by pavers butting up to the edge of the completed oven. If dirt, leaves "stuff" did, make its way into the recess it would simply be a matter of removing some pavers and either hosing out or blowing out. The idea is that the oven is permanently off the concrete floor so never can absorb moisture. Also will have a 150mm flue and be covered either in small tiles with grout or some kind of waterproof render.

My basic motive was to cook some pizza, but then we added maybe cooking a roast the next day, or baking some bread and cakes. So chasing some advice / feedback

1. Is this overkill? Considering I was only originally happy to spend a couple hundred dollars, now I'm up around the $1400 mark.

2. Would a simple vericrete dome with a layer of ceramic blanket covered in more vermicrete on a vericrete slab with some firebricks inside suffice.

3. Is poor mans home made concrete dome mix (3,1,1,1,) much worse than proper refractory cement. Is there more chance of cracking. Is there less heat retention. Cant believe it's $90 per bag of the good stuff. and I need around 10 of them.

4. Is the 35mm Fire brick floor thick enough without the 50mm additional Refractory layer beneath it or should I keep the refractory layer there.

5. Could I ditch the 100mm vermicrete insulating layer under the refractory cement flooring and just have the Fire bricks on refractory cement on Fibre Cement sheeting as insulation as it is off the ground.

6. Floor height will be around the 1m mark, I am 6 ft, Minister for War & Finance is quite a few inches shorter. Do you think this height is OK, or should I lower it a bit. Seems about right for me, but maybe a bit high for her. Should I lower it a couple inches.

I would rather build it properly than have to rebuild it again. I think I've just answered my own questions.

Thanks in advance.

JB