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carloswlkr 06-14-2007 08:34 AM

igloo vs. gabled wall for oven in the tropics
I am about to begin construction on my Pompeii Oven here in Costa Rica. It rains 8 to 9 months per year, with a fair number of heavy, torrential downpours per month. Our outdoor kitchen is covered, but the oven will be sticking out about four feet (most if not all of the dome itself). I've finally found sources for vermiculite (medium and course agricultural grade) and perlite. Fire bricks here are called 'refractory', and are a pale yellow / pale beige color. I plan on using them and a pre-mixed refractory mortar that is supposed to be appropriate for high-heat ovens.

My questions, before I begin, are mostly to do with waterproofing the oven. I've read about the various layers on the igloo style, finishing off with a waterproof stucco. But I wonder if this is enough in an area where it rains so much. Also, the brick mason who was originally going to build the oven (I'm no longer going to hire him, rather do it myself) said that there is so much expansion in an oven that there are often cracks and water seepage. He builds exclusively barrel style ovens (doesn't know how to build or trust the dome shape), so I wonder if that is more of a problem in barrel shape vs. dome.

Would an Igloo style with sufficient insulation and waterproof stucco suffer from heat expansion and cracking, and be vulnerable to heavy rains? If so, should I go with a gabled roof style instead?

Many thanks in advance, and I look forward to posting pictures as I begin construction!


DrakeRemoray 06-14-2007 09:00 AM

Re: igloo vs. gabled wall for oven in the tropics
I personally think that the gable house will provide a drier oven.

My other concern would be this "pre mixed mortar for high heat ovens". Does it come in a tub or a bag?


carloswlkr 06-14-2007 02:02 PM

Re: igloo vs. gabled wall for oven in the tropics
Thanks for the quick reply. Not sure about the mortar, but will ask before I purchase it. I've been given the option by the brick supply company of either 'tierra refractaria' (which I am told is basically the same composition of the bricks, but in powdered form) to mix with cement for the mortar, or this other 'Reframix' which is pre-mixed refractary mortar. They say the pre-mix is for high heat applications, or ovens that will receive high use.

Any suggestions on where to look for the woven ceramic blanket, Insulfrax or similar material?

Thanks again,

CanuckJim 06-14-2007 02:59 PM

Re: igloo vs. gabled wall for oven in the tropics

Where I am the issue is more with snow, and melting snow, than rain, but I think in your situation you'd be much better off with a gabled design. Once the oven is together and insulated, you can go with a standard roof above, without worrying about fire safety issues.


dmun 06-14-2007 03:52 PM

Re: igloo vs. gabled wall for oven in the tropics
You also don't have to make this decision right away. Just leave room for the wall you'll need for the gabled enclosure, and stick a few lead anchors into the wet concrete of your support slab, and you'll be good to go if you decide you need more weatherproofing.

I'm all in favor of a proper roof on top of your oven. The vermiculite/perlite does absorb water (that's what it's sold to do) and even a tiny crack in the cladding could get it wet and make your oven slow to heat up.

This week I'm building an enclosure on top of my oven, and it is a bunch of work, but it doesn't have to be elaborate to be effective.

DrakeRemoray 06-15-2007 07:45 AM

Re: igloo vs. gabled wall for oven in the tropics
The Premixed tub mortar sounds like an "air-set" mortar intended for indoor use. 'tierra refractaria' might be a better bet...I googled it but all links are in spanish...

Can anyone else tell Carlos what to look for?


carloswlkr 06-16-2007 11:52 PM

Re: igloo vs. gabled wall for oven in the tropics
I visited the source for the bricks and mortar this morning (it's actually where they make the bricks), having previously only been to a resale outlet close to our house. The reseller didn't quite have the story straight on the mortar options. I still have the choice of the brick powder ('tierra refractaria') to mix with cement, or to buy their package of 'reframix' which turns out to be just a 20lb bag of the 'tierra refractaria' and a 20lb bag of what looks like white cement, to be mixed with water at the construction site. They do sell a refractory mortar, but the sales guy said that it is intended more for kilns than for food ovens. I'll go with the 'reframix' and see how it turns out, unless someone suggests sticking with just the 'tierra refractaria' and portland cement.

The trip also opened up a new option for fire bricks, though, and I'd like to know what others think. I can buy the standard rectangular shape brick, or tapered firebricks (sold for arch structures) for about the same cost. The wedge shape is available in different tapers. I don't have the exact dimensions, but they all have the standard length and width, and the height that forms the wedge is available in 1" to 3" or 1 1/2" to 3" and 2" to 3" tapers. I am curious about using these, cut in half and laid on their flat side, to build the dome. There is talk of this towards the end of the thread on dmun's geodesic concept, but does anyone have any updated thoughts for a newbie? Should I stick to standard, rectangular firebricks, and use wedges or shimmeys and a healthy amount of mortar? Or slightly modify the Pompeii design using tapered firebricks instead of the wedges?


james 06-17-2007 02:22 AM

Re: igloo vs. gabled wall for oven in the tropics
There are a couple of ovens being built in Australia using tapered bricks -- which cost a lot more than standard firebricks there. If you can get tapered bricks for a reasonable cost, that sounds promising.

You will do less cutting and use less mortar and wedging.

RTflorida 06-17-2007 05:12 PM

Re: igloo vs. gabled wall for oven in the tropics
If you can get tapered bricks for the same cost as straight, go for the tapered. Far less cutting and less mortar. you may spend a little time in planning, but the benefits of the above, far exceed a little extra planning.

I wish I woud have had the option of tapered.....local suppliers wanted a minimum of 4 times the cost of straight; with the cost growing with each higher degree of taper.

carloswlkr 06-18-2007 01:49 PM

Re: igloo vs. gabled wall for oven in the tropics
Thanks for the replies. I reconfirmed this morning that the price for the tapered firebricks is in fact the same as for the rectangular ones ($1.35 each). Turns out, they offer 24 different taper sizes! Looks like I'll have some measurements and calculations to do, but might be able to do most of the dome in pre-tapered bricks.

Back to the waterproofing, Dmunn, how is your rubber pond liner holding up? Has anyone else used a similar water barrier between the vermiculite / ceramic insulation and the finished surface?


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