Rock wool as insulator?

[altamont]

Re: Rock wool as insulator?

I can not locate the thermal calculator I used a while ago, but I can assure everyone that Mineral Wool insulation is perfect for wood fired ovens. Each insulation has thermal properties different from others and have specific temperature ranges where they are superior to others. Industrial furnaces typically use mineral wool as an insulator next to the "hot face" refractory (the fire brick in our case, ceramic fiber in others). This is because it insulates better at those lower temperatures.
I personally used mineral wool board too on my oven (and would have preferred blanket as well).
I would recommend a layer of ceramic blanket between the brick and this mineral wool for those that need that extra sense of security and peace of mind and do not mind the extra expense for the blanket.
However, I feel that it is not always required because the heat that is conducted through the brick (or leaked out through any cracks) in our wood-fired ovens is not high enough to have a negative impact on the mineral wool.
A plus in tayloring the insulation (or insulating layers) is that less heat is conducted away from the hot face material which results in more heat staying in the brick. This can result in less fuel consumption and longer heat retention.

[GianniFocaccia]

Re: Rock wool as insulator?

Altamont,

Are you recommending tailoring mineral wool board (ie: a geodesic shell) around the dome with ceramic blanket in between?

[altamont]

Re: Rock wool as insulator?

I am not strongly recommending using mineral wool board - it is much harder to work will as it just does not bend. If only the blanket form of mineral wool was easy to find...

My thought was that one layer of ceramic blanket between would give some people some peace of mind. It is used as a hot-face lining in many industrial furnace designs so it can very easily withstand the much cooler temperatures between the firebrick and mineral wool. It would partially fill some of the void between the curved brick surface and the flat surface of the mineral wool board and not slide down from gravity (in the more vertical areas of the dome).
I still have to come up with the chimney on my oven and a weather-proof house for the dome. Much to my chagrin, I can only fire up in good weather - everything is now covered up under an ugly blue tarp to keep the mineral wool dry :-(
I can say that I have fired the oven up to clear, maintained a small fire on the side and fired pizzas on the first evening. I put 2" thick cal-sil board up as a door. Open those up two days (evenings) later and I am still over 350 F. on the sidewalls and top of the dome (inside of course). Ambient temps the last time I did that and took measurements were @ 70 - 75 F. peak during the afternoon and down to @ 47 - 52 F. at night. Just the one layer of 2" mineral wool board covered by the tarp (only when not firing).
I plan on keeping that mineral wool in place and using up the remainder of the box about the top. Then back fill between the outside walls when built and the mineral wool with bulk fiberglass insulation.

Getting back to you question, if someone had the patience to cut the mineral wool (and taper the joints for tighter fit) - well that would be great. Any openings between pieces of mineral wool are basically uninsulated voids. If blanket were under the mineral wool, there would be some insulation instead of none.

[SCChris]

Re: Rock wool as insulator?

John, I found that the board wasn't what I was expecting with regard to flexability, but I was able to get the board around the oven. I think you can find thinner boards than what I used and you might be able to split the boards. If you're enclosing your oven then the boards work just fine and the're available at a good cost. I don't think that unless you had a very large crack that vents flame through the dome rather than out the flue, that Mineral Wool have any problem. For a stucco covered dome you might have real problems getting the insulation in a dome shape ready to stucco. If you need a local source send me an E.

Chris.

[GianniFocaccia]

Re: Rock wool as insulator?

Thanks, Chris. My original plans were to use ceramic blanket and vermicrete followed by loose vermiculite housed in a cement board enclosure like yours. However, if I was able to source a case of insblock 19 like I did for my oven floor insulation ($75 for 8 3'x1'x2" boards), I might think about it. Although Dmun recommends just using more ceramic blanket, I like the idea that ceramic blanket is best used in direct contact with a 'hot face' and Insblock is best used as a backup insulation layer in kilns. I would separate the 2" thick 2-ply boards into 1" boards, and maybe have enough to cover my dome. I'll have to do the math first.

[v12spirit]

Re: Rock wool as insulator?

Hello everybody
Can any one tell me the difference between mineral wool and rock wool? Actually I could not find insulation stuff suppliers and determined to use the insulation blankets used in refrigerators that I can get from scrap dealers. Is that substance rock wool or mineral wool or what is it? I'm just afraid it burns out if I clad the dome with it.
Thanks

[david s]

Re: Rock wool as insulator?

I've used rock wool blanket. It is not quite as good an insulator as ceramic blanket, it is harder to cut and is far more water absorbent.Good for 650 C, it is cheaper than ceramic fibre blanket and is not classed as toxic like some ceramic blanket. Its density is much the same as ceramic fibre blanket and so it doesn't compress when you work vermicrete or cement shell over it.

[cobblerdave]

Re: Rock wool as insulator?

Hello everybody
Can any one tell me the difference between mineral wool and rock wool? Actually I could not find insulation stuff suppliers and determined to use the insulation blankets used in refrigerators that I can get from scrap dealers. Is that substance rock wool or mineral wool or what is it? I'm just afraid it burns out if I clad the dome with it.
Thanks

G'day
Mineral wool is man made fibres.
Fiberglass up to 260C
Rockwool up to 850C
Ceramic up to 1200C
I'll hazard a guess in saying anything used in fridges would not be heat proof in any way. Commercial walk in fridges are usually built of plastic foam sandwich construction. Even domestic ovens do not operate above 300C and that mainly those with a self clean ability.
I don't think either fridges or normal stoves are built for 600C the upper temp expected from a WFO. Including there insulation.
Regards dave

[stonecutter]

Re: Rock wool as insulator?

Hello everybody
Can any one tell me the difference between mineral wool and rock wool? Actually I could not find insulation stuff suppliers and determined to use the insulation blankets used in refrigerators that I can get from scrap dealers. Is that substance rock wool or mineral wool or what is it? I'm just afraid it burns out if I clad the dome with it.
Thanks

Same thing different name. It's what I used in tandem with perlite or vermiculite in all my ovens so far.

[v12spirit]

Re: Rock wool as insulator?

I've used rock wool blanket. It is not quite as good an insulator as ceramic blanket, it is harder to cut and is far more water absorbent.Good for 650 C, it is cheaper than ceramic fibre blanket and is not classed as toxic like some ceramic blanket. Its density is much the same as ceramic fibre blanket and so it doesn't compress when you work vermicrete or cement shell over it.

Thank you everybody
david, I did not understand how rock wool blankets do not compress, I mean when used for insulating the floor. Would you clarify more about the vermicrete shell and how it prevents compression?
By the way, is vermicrete the same as vermiculite?

[cobblerdave]

Re: Rock wool as insulator?

G'day
Seen a wool carrier catch fire in Singapore harbour, they couldn't put it out due to the water not being able to penetrate the bales . They tried to tug it to sea but it sank in the strait. The water was still boiling a week later when we sailed.
Wools fairly fire resistant , but resistant only , its still organic and will burn.
Regards dave

[wotavidone]

Re: Rock wool as insulator?

We are having a major maintenance stop on one of our plants. So today I walked past a truck loaded with rolls of stuff labelled "Firewool". Blankets about 2 inches/50mm thick backed with a foil layer.
Why is it that offcuts of stuff like this never turn up in our salvage yard?

[stonecutter]

Re: Rock wool as insulator?

By the way, is vermicrete the same as vermiculite?

Vermicrete is made by blending Portland cement with vermiculite at the desired ratio to form insulating slabs or cladding.

[stonecutter]

Re: Rock wool as insulator?

Wools fairly fire resistant , but resistant only , its still organic and will burn.
Regards dave

The mineral he should be using will not contain organic material, and will not burn. The products I use are made from basalt, and have a melting point of 2150* which is more than sufficient for a WFO. If an oven reaches that point, insulation vitrification is only going to be one of your problems.

Ceramic fiber is usually up to 3200*...it is premium insulation, but mineral wool can be just as effective.

[david s]

Re: Rock wool as insulator?

Thank you everybody
david, I did not understand how rock wool blankets do not compress, I mean when used for insulating the floor. Would you clarify more about the vermicrete shell and how it prevents compression?
By the way, is vermicrete the same as vermiculite?

When I said it does not compress that is not quite correct. Both rock wool and ceramic fibre blankets are around the same same density and when used between the inner dome and outside shell are sufficiently dense enough not to compress when working against or over with vermicrete (cement and vermiculite) or cement render. If you used the stuff under the floor it would not be strong enough to resist the weight and would compress, you need something stronger than blanket for that application, preferably cal sil board or 5:1 vermicrete. For my first oven I used fibreglass ceiling insulating bats over the dome and although they worked pretty well, they did not degrade or burn as some people have suggested, they did compress because of their low density which made working over them quite difficult.