For experts and/or experienced builders!

[dmun]

Re: For experts and/or experienced builders!

I will go with glass wool batts!

Bad idea. They have an organic binder that burns and stinks at oven temperatures.

I was able to find through an eBay like website (MercadoLibre) a supplier of perlite instead and it is much cheaper than the vermiculite? So my question is; how does perlite compare to vermiculite as an insulation material and can I go with the perlite without losing insulation properties?

They are functionally identical. I used perlite concrete on top of a thin layer of refractory blanket over my dome. Perlite concrete works fine, you just need twice as much of it as refractory board/blanket.

Would you choose glass (broken or whole bottle?) for the oven floor insulation over glass wool?

I wouldn't use either one.

[david s]

Re: For experts and/or experienced builders!

Onyxx,
If you have access to perlite then use it mixed with cement 5:1 as your floor insulation. It is a slightly better insulator than vermiculite so if you can get it cheaper you"re onto a double win. I did say the broken glass should only be considered in the absence of other, better materials. Don't even think about using fibreglass bats under the floor, they will just squash flat and therefore not insulate.

[brickie in oz]

Re: For experts and/or experienced builders!

I really fail to see how glass broken or otherwise is a good insulator?
One hot piece of glass with transmit its heat to the next piece of glass etc.

It just doesnt make sense.

[david s]

Re: For experts and/or experienced builders!

The thermal conductivity of glass is 1.05 compared to dense brick 1.31, concrete and mortar 1.7 so it's not that bad. It is the air trapped between the material that creates the insulation value, after all glass and clay are transformed into fibres to create ceramic fibre insulating blanket and fibreglass insulating batts. What seems the important factor is the resulting density of the material you end up with. With pieces of curved glass from broken bottles, the contact points are reduced significantly and the spaces between them are maximized. The addittion of cement to perlite or vermiculite also reduces the insulating value too. I'd still not use broken glass if I had access to better materials.

[brickie in oz]

Re: For experts and/or experienced builders!

The thermal conductivity of glass is 1.05 compared to dense brick 1.31, concrete and mortar 1.7 so it's not that bad.

So its just slightly better than dense brick? I can now see how it would be a good insulator.....

[Aegis]

Re: For experts and/or experienced builders!

I am NOT an experienced builder, although from an engineering background, isn't broken glass insulation the basis for making the product foamglas? Instead of broken glass with air in between, it is tiny glass ballons with co gas inside! So it would be the ratio of glass to air space that is important for R value. I think the glass gives compression strength to the product.

[Onyxx]

Re: For experts and/or experienced builders!

Hi guys!

First let me just explain the real reason we are discussing this issue; it is not because I want to be ?different? and use unconventional materials such as glass, salt, sand, etc. as insulation (Yes! I know sand and salt are NOT insulation materials). You need to remember (or know) that I am not in the US, I am in a third world country and NOT even on the capital city of that third world country where things are more ?accessible?.
Access to materials that are consider unconventional here, (vermiculite, perlite, ceramic blankets, etc.) are both hard to find and very expensive.

So that being said, I?m still thinking (just thinking) about using glass as an insulator. I just want to see if there is a better way of making use of it.

Brickie in oz wrote:
I really fail to see how glass broken or otherwise is a good insulator?
One hot piece of glass with transmit its heat to the next piece of glass etc.

Remember that it is air the REAL insulation here and NOT the actual glass. In other words, the glass is used to create air bubbles.
But I definitely understand your point! What if somehow we can use glass to create air bubbles but insulate the glass itself preventing one piece of glass from touching another and/or transmitting heat by proximity?

On the use of glass wool batts, dmun wrote:
Bad idea. They have an organic binder that burns and stinks at oven temperatures.

I thought a LOT about that. What if I was to (if I decide to go with the glass wool) wrap the oven with it (after the dome is cured of course) fire up the oven, get it really hot and repeat the process until the binder burs off and only THEN finish the oven with a sealant coat?

Come on guys!!! Think think think...

[stoveup]

Re: For experts and/or experienced builders!

I think the problem with broken glass as an insulator is the thickness of the glass pieces. When glass is transformed into good insulators like fiberglass bats or foamglass boards, the glass material is extremely thin so it is not able to hold absorb and transfer a large amount of heat. The insulating air spaces in these products are also small, but are very large when compared to the thin glass cross section.

Other forms of glass (bottles, jars, window panes, etc.) are relatively thick which enables the material to absorb a large amount of heat that can be transferred through the glass itself. The contact points between adjacent pieces of the broken glass create a network of conducting highways for heat to follow on its way out.

My preference would be to avoid using broken glass if at all possible. If you have access to perlite, perlcrete will be easier and safer to work with and will provide much higher insulation value for equal thickness.

Good luck with your build!

[brickie in oz]

Re: For experts and/or experienced builders!

Come on guys!!! Think think think...

I think you should use glass as an insulator and then report back in the future.

This way we can all get the facts on how good/bad glass really is for an insulating material in an oven situation.

[Onyxx]

Re: For experts and/or experienced builders!

I?m sorry brickie in oz, I did not mean anything by my last remark... just trying to be cute!

Anyway, I thought the whole idea of a forum (at least this forum anyway) was to get feedback, tips and good advise from people such as yourself. You know, people with experience and knowledge to share.

And yes, of course, whichever way I decide to go regarding the insulation I will post my results here.

Thanks man.

[brickie in oz]

Re: For experts and/or experienced builders!

I?m sorry brickie in oz, I did not mean anything by my last remark... just trying to be cute!

Anyway, I thought the whole idea of a forum (at least this forum anyway) was to get feedback, tips and good advise from people such as yourself. You know, people with experience and knowledge to share.

And yes, of course, whichever way I decide to go regarding the insulation I will post my results here.

Thanks man.

Dont apologize, really.

This debate about glass as an insulator has been going on for many a thread for months and I would seriously like to know once and for all if it works or not, hell I could save big bucks on my next oven build if it works.

[Onyxx]

Re: For experts and/or experienced builders!

Well, you know, I am thinking of a way to use glass to create air "chambers" that just might work (this idea calls for the use of vermi/perlicrete as well).

I am finishing a ruff drawing of my idea and I will upload it in a bit. I really want know what you and the rest might think of it!

More to come?

[RTflorida]

Re: For experts and/or experienced builders!

Onyxx, you are in Argentina?
Are there not 30+ extinct and active volcanoes in Argentina? I would think lava rock in any form would be better than glass or any of the obscure materials listed.
You may not be in Rome, but it may not be a bad idea to do as the Romans did.
Just a thought.

RT

[Onyxx]

Re: For experts and/or experienced builders!

Ok, here is a drawing of what I was thinking. You need to imagine the glasses closer together, as much as possible (and they may be replaced by empty bottles, in fact, I think that using bottles maybe better but I did not want to make another drawing).
These are regular (and very cheap) drinking glasses, with the glass it self being very thin to keep the thermal mass down as much as possible.
I did not include any measurements because? well I have not thought about that yet?

What do you guys think? Am I missing something here? Does this design have a terrible flaw somewhere that I do not see?

Remember, I am just asking if you think this could work? I am not looking to replace ceramic blankets, vermicrete or any other already proven insulation.

[Lburou]

Thinking outside the box has risks.....

I recognize you want to think outside the box. But go slowly if you deviate much from the proven materials recommended in the fornobravo plans. Going slow enough will give you plenty of time to come to your senses and listen to the consensus of advice already offered to you

Don't use glass. The pompeii oven plans are based on the successes and failures of real people like yourself. Find a way to use good/efficient insulators. RT has suggested what may be your best alternative. When you've poured a good chunk of money and a lot of hard work into an oven, you do not want unexpected problems, or a forehead slapping 'Ah-Hah' moment when you realize that insulating efficiently was really important after all.

One important distinction you should make in your oven design is the insulation requirements under the oven floor and over the dome. They are different, in that the insulation under the floor must support the weight of the oven. The insulation over the oven doesn't have to support a lot of weight. What am I getting at here? I'm saying that, for insulating under the floor, there is no good glass substitute for vermicrete (OK if you use Perlite)!!

Lava rock, say 12 or 16 inches thick, might do well enough as an insulator above the dome.

HTH