Alternative Insulation

[mikku]

Re: Alternative Insulation

Thank you all for helping me to understand K,R,W,U and their metric counterparts. Far from understanding fully but at least aware of their relationships.

Back to "alternative insulation", I still believe that sand can be used as an insulator effectively. It is used as a medium in the castings of aluminum --it conducts heat away from the molten metal but the outside of the mold can be nowhere near the temperature of the metal--so it is an insulator as well.

How about this scenerio:
Any kind of an enclosure can be made from native materials, wood, scrap metal, stone-- (virtually anything easily available). Make this enclosure or base large enough and strong enough to contain a large quantity of sand.

The site should be high enough so that water does not flow under the enclosure and the bottom of the sand layer should be protected from water to prevent wicking.

Now if you built your WFO on top of this, with a layer of anything that would distribute the combined weights of the hearth floor and the oven dome. The sand would act as an insulating medium.

All the points mentioned before come into effect.
-using the sand to create air spaces.
-making the air spaces captive
-prevent heat loss by conduction (small particle to particle contact), conduction decreases with depth of sand base.
-utilize the sands -"real nature" as a heat sink.
-keep water away to prevent cooling via evaporation.
-a cheap, almost universally available material.

The longevity design success would depend the materials used to contain the sand. Wood & Sticks, vs Cob & Reed, vs Stone & Mortar. And the sub-base which the whole thing is built on.

Is that a "Three Little Pigs" story?

IMHO, water is the culprit in all builds. Because of its "possibly best - fluid conductor of heat", and problems associated with relatively low phase temperature change.

[brickie in oz]

Re: Alternative Insulation

I still believe that sand can be used as an insulator effectively.

Use sand in your build as insulation, then report back and prove the world wrong.

[TropicalCoasting]

Re: Alternative Insulation

...unless he has a commercial bread/pizza oven and wants lots of thermal mass to maintain heat over years and decades (ie. never letting it cool down)

[mikku]

Re: Alternative Insulation

Hello again-"The three little pigs guy!"

I am not trying to prove anyone in the world wrong, or attempting to use it in my build. I can get insulative materials where I am and choose by my budget which to use.

The author of this thread is in Kampala, Uganda and asked about "alternative insulations" and I am trying to rationalize alternatives.

Designs have morphed since the beginning of this forum. Early designs showed pericrete "below" a concrete slab, then a firebrick hearth. Is it that wacky to consider sand a better insulator than reinforced concrete? From what is listed, pericrete isn't that "red hot of an insulator either!" but it works!

I guess the question gets tossed back to NeilB-- "What do you have to work with in Uganda that is plentiful, cheap, has at some insulative values, doesn't melt at oven temperatures, doesn't off-gas hazardous chemicals? From where I am typing, I cannot see Uganda or even guess what the conditions might be.

NeilB--some feedback from you is necessary!

[brickie in oz]

Re: Alternative Insulation

I can get insulative materials where I am and choose by my budget which to use.

Use goose feathers, as this is obviously a wild goose chase.

[mikku]

Re: Alternative Insulation

Looks like "Brickie in oz" had a bad day at work!

What ever the case may be, don't think wild goose feathers are going to work in Uganda. I think it has something to do with trafficing in endangered species or something like that. If they did work in WFO's then geese surely would be endangered everywhere! I never could acquire a taste for the meat either, kinda tough, taste and looked like liver too! Similar to "Eagle" but not as fishy flavor.

From the bottom of the page, it seems like this issue has been discussed at length since almost the beginning of time. That is- "if you use FBForum's creation as year 1"! Should have read more before posting--but too late!

Looking forward to more - ideas for "alternative insulation"!
Always remember, tomorrow is a better day!
BTW are there circle flies out yet?

[brickie in oz]

Re: Alternative Insulation

En contraire mon ami.

I have had a very good day, please dont try to read my mind or intentions or second guess me, they are as written here and above.

You are in Japan, not Uganda, you resurrected an old thread so your question I would assume pertains to your own use in Japan and not in Uganda.

Maybe you could use troll hair or fur, Im sure that will have excellent insulating properties too.

[mikku]

Re: Alternative Insulation

Glad to be mistaken, and that you had a good day!

By the way, I did not resurrect this old thread; I mistakenly entered after several other posts. I was interested in the topic of "alternative insulation" as it applied anywhere.

As I mentioned earlier, I was unaware of previous threads discussing sand as an alternative.. cannot catch up in one month, what people have been talking about for years!

I am still interested in "alternative insulation" as a topic and suggestions of viable materials.

[david s]

Re: Alternative Insulation

The thermal conductivity (k) of dry sand is 0.15 - 0.25 W/mK.
Compared to dry loose vermiculite 0.058 which is about three times better.
But add cement to the vermiculite and it drastically increases the k value.
A 4:1 vermiculite, cement brew has a k value of 0.16, similar to the sand.

Sand is a better insulator than many would think.

[mikku]

Re: Alternative Insulation

Thanks for that bit of information!
I thought I was hearing the voice of God, "as written here and above!"
We have to keep the topic light to promote free expression, and try to read what's been written in its entirety to try to grasp the intent!

[cobblerdave]

Re: Alternative Insulation

Gudday mikku
An old welch bread oven was pulled down in my old town in the 80s/90s . There was a lot of interest in the old bricks, but a lot of disappointment cause when it was pulled apart as there were fewer bricks than you would think. The oven "shell" was brick and the outer housing was brick held together by long steel bars and S shapes plates. All the internall of the oven was taken up with sand...the sand was basically the the mass of the oven not an insulation. That oven was basically fired 24 /7 and the outside never got hot because the thing probably weighted 30 or 40 tons.
You will want to insulate your oven because you will not want to have a fire in your oven at all times ( a welch oven has a separate fire on the side outside the cooking space by the way)
Regardless of the "R" value ,the efficiency of the insulation , the thickness is important as well remember. 6 ins of pearlite/cement insulation is equal to 2 inch of ceramic insulation.... It does the same job only it's thicker.
So if you say go for a clay/ straw like used in a cob it would have to be quite thick I would think.
I read of a common brick oven with a clay/straw insulation layer then a final layer of common house insulation over that. I insulated my own oven with 2 in of ceramic then planned to finish with pearlcrete . Ofter 2 attemps to get the blessed stuff to stick without wreaking my expensive ceramic I finally used domestic "rock wool" for the final layer. I have opened the shell of the dome up and checked the insulation layers out no problems the ceramic takes the initial heat and the rockwool is still good.
With cob ovens with clay/straw insulation they are usually lime mortared over the top of the insulation . A flexible lime based mortar ( or cow poo for the purists) is usually used because a cement based one would only crack with the expansion/contraction of the oven. This means the oven would need overhead protection. Using a layer of rockwool type insulation allaws you to use a cement lime mortar an gain a measure of water resistance.
By the way investigate " rice husk ash " it's used in Thialand as an insulation for kilns and houses. A product I know little about but I suspect is cheap and locally available rather than efficient .
Hope something here is a help

Regards dave

[mikku]

Re: Alternative Insulation

Hello Cobblerdave- glad to make your acquaintance!
My build has progressed to the point of placing the precast dome sections on top of the firebrick hearth. Because of cost considerations, I have a 4" layer of 5:1 peri/vermiculite insulation beneath only!

I have not decided on dome insulation, but the blankets look as expensive as the mat right now. Have not looked into rockwool as an insulator yet. At this point, was trying to determine the procedure for application from the dome to insulation--if any break was necessary. I assume not, but possibly something initially that would retard the water from being instantly sucked from the pericrete on contact with the dome.

Rice hulls are usually just tilled back into the "tombo" rice fields. But since 3/11, some farmers just stock pile them. In the past, alot of it was burnt in piles right where the cleaning machines blew it. Other usage is for cow bedding. All these situations --the raw hulls would be "free"! But there is also concern about the amount of Cesium contained in these raw hulls; more so if they are burnt to ash. I do not know what to think! The distance from my house to the crippled reactors is not that far! Similar concerns are for "ash from woodburning stoves", we are told to put these ashes with our regular "burnable" waste and it goes through another incineration at the disposal station that has scrubbers. We have radioactive substances that keep cycling through the ecosystem. Gets deposited by wind and rain on vegetation, as leaves fall and dispose, goes into soils, it gets picked up by the plants and distributed through them to roots, leaves, etc. some plants more succeptable to building a concentration. The cycle continues--some gets transported to rivers and streams etc. The level of exposure is minute at best--I will probably never see any ill effects, future generations might?? I really feel no danger, just aware that things could have been different if the designers of the plants were more careful to design in back-ups.

My instructions on the castable is to do staged firings.. probably same as for brick ovens. It looks like the brick ovens are fired before any additional insulation is added. I wonder if that is true for poured castable refractory as well?

Just some thoughts?

[mikku]

Re: Alternative Insulation

Cobbler dave!
"I had a dream", and it woke me up! A famous man used those words and they continue to ring to this day!

I had to tell you that you proved my point inadvertently.

Like lots of things in nature, materials possess multiple characteristics!

You described the decommissioning of a bread oven that had been in operation almost continuously for a very long time. Also, that to everyones dismay, that instead of being constructed of multiple layers of brick- it contained a huge amount of "DRY SAND"! Further pointing out, because of its 30T mass, it remained cool on the outside!

If sand is a conductor only, then this oven over time would have absorbed so much heat that the interior and exterior would be similar temperatures. It is a natural action! Heat goes to cold --- attempting to reach equilibrium-- irrelevant to direction.

Heat doesn't rise! Warm air rises because it is "lighter"!

You did not mention any other material in the disassembly aside from some steel rods, plates and strapping. So in the absence of anything else, you have proven that "sand" is a very good insulator as well!

And that the Welsh realized it and used it! Cheap and plentiful-- but it requires a bit of space to make it useful!

The points others made and that I listed are all important:
-For sand to insulate, it has to be dry!
-It must be contained to be effective, not allowing for convection to occur.
-at some thickness, the characteristic changes (conductor) to insulator. Uniform sizes, minimal contact, captive air!

Great! I love it!
"Goose feathers also are buoyant, flexible, water repellant, and extremely strong besides being a good insulator" But their characteristics change if they become soaked in water!

It also proves that a forum works! A lot of information, from a lot of different sources, mixed together and a light pops on! Or a goose egg! I guess it is all in how you look at things!

Have to get back to sleep! Today is going to be a very busy one, I am glad it started out so well!

[david s]

Re: Alternative Insulation

Another cheap and plentiful alternative for insulation would be to use straw.It is a wonderful insulator as used in straw bale houses. If insulating an oven it would be better to use just enough clay mixed with it so the stuff will stick, bearing in mind that the more heavy material you add in the mix the more you reduce the trapped air and hence it's insulating value.The issue of the straw burning is hardly a problem. If any burns then you are just left with some carbon and an air space. Because there is next to no oxygen available the stuff will only char next to the inner oven walls.
By the way this thread is not an old one in fact it's only a week old.

[ATK406]

Re: Alternative Insulation

[QUOTE=mikku;145292]Cobbler dave!
[B][I][U] -For sand to insulate, it has to be dry!
-It must be contained to be effective, not allowing for convection to occur.
-at some thickness, the characteristic changes (conductor) to insulator. /QUOTE]

Hello Mikku,
I agree with most of what you said there except for that last bit. It may just be a matter of semantics and I suspect that you understand this better than you let on. However I think your use of the terms conductor and insulator and the "changing characteristics" of sand needs to be clarified;

The terms conductor and insulator are meant to characterize the relative property of thermal conductivity. In a similar way these terms are used to characterize the property of electrical conductivity. As with electricity, all materials conduct heat. Good conductors transfer heat at a higher rate than poor conductors. Poor conductors are called insulators and good conductors are called...conductors and are sometimes used as a heat sink.

The thermal conductivity of sand does not change (unless is melts). Rather it is the thickness of the sand layer and the temperature gradient through it that determines the rate of heat lose to the environment - if you don't count the heat lost to the sand itself.

A thick layer of sand on a WFO will reduce the amount of heat lost to the outside environment and to that extent it is an insulator. However it will also absorb a lot of heat, acting as a heat sink, which is also heat lost from your oven. To be sure, an oven insulated with a ceramic blanket will also lose heat to the outside environment (albeit at a lower rate) but the blanket will also absorb less heat - meaning less heat loss. As David S pointed out, dry sand and vermicrete have very similar properties of thermal conductivity. However density and heat capacity are also important properties to consider when selecting insulation material. I suspect that vermicrete has a lower density and heat capacity than dry sand.

The brick and sand oven that C. Dave described was probably intended for continuous usage where the high heat capacitance of the sand was not an issue. The sand was surely there as a heat sink to keep the oven warm for days on end. You certainly wouldn't want to heat up an oven like that from a cold start. I don't think you would want to insulate your oven with sand for much the same reason - and a beautiful oven it is! Unless you suspect that you don't have sufficient thermal mass in which case 3-4 inches of sand might be good.

That said, the cost of insulating (or conducting) materials must vary greatly from region to region (as with everything else). I'm sorry I don't have any new or exotic suggestions for insulating your oven....Maybe a layer of hollow duck eggs dipped in a lime based mortar, wrapped with a wool blanket soaked in a lime/cement slurry? That's probably not as good as the "Troll Fur" recommended by Brickie....I don't have any of that here, but if you ask him really nicely, I'll bet he will give you some. It sounds like he has an abundance!

Good Luck with the rest of your build...though judging by the great skill you have demonstrated so far...luck will have nothing to do with it.

Kind Regards,
AT