Insulation bricks

[ricocamus]

Re: Insulation bricks

Sand and Salt are traditional insulators, but they aren't very efficient, because they don't trap much air. Aren't the Philippines volcanic? Can you get some kind of light weight volcanic rock like pumice or tufa? That would be almost as good as vermiculite.

Pumice should be relatively easy to get. Pardon the ignorance, but would you crush the pumice to mix it up in the concrete for the hearth? Or would you the stones? I guess it depends on the size of the pumice stones.

I'd be really interested to hear what you think. At this point, finding vermiculite is one of my materials issues.

[dmun]

Re: Insulation bricks

Sand and Salt are traditional insulators, but they aren't very efficient, because they don't trap much air. Aren't the Philippines volcanic? Can you get some kind of light weight volcanic rock like pumice or tufa? That would be almost as good as vermiculite.

[del]

Re: Insulation bricks

Hello to everybody,

It had been quite a long time that I had just been lurking here. Finally I had finished my oven and it is doing well now. Thanks to all tha suggestions given here. As per suggested it seems I am the only one wh0 owns an oven around here which did not make use of salt as insulation. Nevertheless I am very much satisfief with the result of my oven using sand as insulation instead of salt. And sand was much cheaper. Rico for wood I practically use anything as long as the wood I know is not poisonous. Actually my problem transporting wood for I dont own a vehicle. This made my overhead more expensive but that would not kill my enthusiam. Cheers!

[ricocamus]

Re: Insulation bricks

Hello,

I am fromthe Philippines and it seems as I ask around here they only use same all red bricks for hearth, walls and dome. They also use sackful of sea salt underneath the hearth. Any comment please. I am due to start my brick oven very soon. Thanks

Del,

Also from the Philippines and looking at options. Did you build your oven? Any feedback you can?

What kind of wood do you use?

[del]

Re: Insulation bricks

Wow!! thank you everybody. You really amazed me with your instant replies, I am so overwhelmed. Hugs to all.

The all red bricks oven here in our place had been working since pre-war. That same old bakery had nourished three generations as I ask around. They had remodelled their bakery but they never demolished their old reliable old fashioned oven and that made them unique among the other bakeries. Maybe some ovens had been rebuilt. Again thanks to all the people here. May your tribe increase.

[james]

Re: Insulation bricks

Welcome aboard Del,

If you can't find the modern insulators, the traditional ones work fine. I have never used salt personally, though I have heard many builders talk about it. I have installed an oven using sand, and it worked out OK.

Any ideas on the thermal properties of salt? Would you put the salt under the oven and over the sand? I can't help here.

You definitely want to make sure your enclosure is water tight. The salt and sand will suck up moisture and your oven won't cook until it fully dries out.

I also think that red bricks are OK, if you can't find firebricks. A lot of folks (myself included) built Scott ovens with red brick domes and firebrick floors and they work OK. The downside I am told (though I haven't been looking at ovens long enough to see it happen) is that clay bricks spall, which is to say they start to flake off, after many cycles of heat up and cool down. Still, for a residential oven, that is something you can live with.

I say go for it. Have fun and enjoy your oven, and let us know how it goes.
James

[Xabia Jim]

Re: Insulation bricks

My two cents on insulating bricks is they are generally not as strong as firebricks. Use them for insulating is great but I would protect them if I could on both the inside (splits?) and outside (stucco?) if I was going to build with them.

I had a great woodstove lined with these bricks but over time the bricks deteriorated from the heating and cooling cycles of wood firing. We used mainly oak which is very hot and remember that surface temp on the door would go to 500 or 600 degrees.

Now it did take 10 years until I ordered new bricks to reline the stove.....

[Xabia Jim]

Re: Insulation bricks

Agreed, salt is a rock substance but it's soluble in water. Be careful!

There are many problems here from saline water being used in the masonry. Now and then this area slips into a bad drought. When that happens there is more of a tendency to mix cement with some saline water. It plays hell later with the masonry as moisture wicks in and out of the cement. The mortar basically deteriorates over time so the stucco just falls off the wall.

So, if you can avoid salt I would. If not, I'd try to make sure it's well encapsulated....or maybe find a binder?? I'd go with sand or gravel before salt.

(The rest of the story is that many years ago the drought was so bad they pumped salt water in the water supply....ruined the old galv. steel plumbing. Now we have a desalination plant and rampant new building all over)

[maver]

Re: Insulation bricks

Del, you're not the first person to bring up the idea of insulating with salt:

http://www.fornobravo.com/forum/f2/variation-heath-base-301.html?highlight=salt+insulation

- I suppose you really need to be sure water does not reach that layer of the oven - waterproofing the exterior or a solid enclosure would be important. Less of an issue if the oven is being used with great frequency, but imagine what happens to the oven insulation if you shut the oven down for a rainy offseason?

As to red bricks, see this discussion:

http://www.fornobravo.com/forum/f8/red-bricks-536.html

I am interested to hear more feedback from others who have used materials different from the conventional materials in the pompeii oven plans. How do they affect oven performance? I imagine a variety of insulators could work. Red clay bricks likely are more of a concern, but if it's all that's available and you are not counting on it lasting forever, build your oven. But please, report back how it works (heat up times, pizza cooking times, duration of heat retention, and whether the bricks break down from the heat).

[dmun]

Re: Insulation bricks

It depends on the size of the bags. A big bag of vermic/perlite in the states is 4 cubic feet, and three may be on the scanty side for a 39" oven. Bags of refractory mortar are fifty pounds, and three sounds about right. I used less, but I made a smaller oven and cut every brick.

[del]

Re: Insulation bricks

Hello,

I am fromthe Philippines and it seems as I ask around here they only use same all red bricks for hearth, walls and dome. They also use sackful of sea salt underneath the hearth. Any comment please. I am due to start my brick oven very soon. Thanks

[maver]

better than vermiculite

They insulate better and are easier to handle - should be much better.

[beammeup]

OK thanks for all your input. If I understand this correctly the insolation bricks have excellant thermal Conductivity (very low at 0.16 w/mK). At 3" thick I think I will just dry stack them on my base, under my fire bricks. They are less than a dollar each so not very expensive. At this price would they be a better option than Vermiculite?
Thanks again

[james]

Good question

Maver,

You have this exactly right. Every brick oven is comprised of two elements -- those that absorb and hold heat (a thermal layer) for cooking and those that stop heat (an insulating layer), and keep it inside the oven. I'm sure Alf will answer this as well, but I think his comments were relative to the merits of the insulating layer. An oven made from all insulating material would never get hot, it would just vent hot air out the front door.

Historically, the thermal layers were clay and the insulators were sand, pumice, expanded clay, and ground glass. Then, modern science took over, and today we have easy access to engineered refractories (a Forno Bravo oven), Insulfrax and SuperIsol (and vermiculite). The ovens heat up faster and insulators work much better. While, the basic design has not changed for 2,000 years, the materials changed in the past 5+ year. Ancient Rome meets NASA.

If you live in a place where you can't easily find Insulfrax of a Forno Bravo oven, the traditional materials work very well. Go for it. For everyone who can access the other materials, you have the best of both worlds.
James

[maver]

"I've taken to bits and repaired ovens and furnaces that have been built with insulation firebricks and they all seemed to work ok." -Alf

So how would building an entire oven out of insulating firebricks relate to the thermal mass design principle? My understanding was the firebricks or the refractory modules such as Fornobravo sells are able to store and then radiate heat to keep the oven temperature even and allow retained heat baking after the coals are raked out. Does an oven made of insulating firebrick heat up faster? Is it harder to maintain an even temperature? Are people able to do retained heat baking? Curious.