Insulation Efficiency

[wemme]

Re: Insulation Efficiency

Does anyone know how the older Clay / Cob Insulations with sawdust or straw compare to perlite and vermiculite concrete?

It is looking like my insulation cost will be about 150% of my Thermal mass cast layer!
I can get all the other cob technology items for free or at least cheap.

has anyone tried Styrofoam bean that are used in bean bags combined with clay/concrete for insulation? even thought the beads break down at low temperature they will leave an air pocket in the clay.

[david s]

Re: Insulation Efficiency

Anything that will bind the vermiculite will work, maybe even flour, but adding mass with either clay or cement reduces the efficiency of the insulation. Use as little binder that you can to retain plenty of air spaces for max insulation efficiency.

[wemme]

Re: Insulation Efficiency

Hello
Is it possible to use only perlite portland mix only as insulation and what thickness would you recommend I've been thinking of 100mm (4") in the base and 200mm (8") on the dome?

What is the usual price of the insulating blanket in peoples areas?

Has anyone tried Clay slip and saw dust which I have read of in a few books now?

Any one done clay slip instead of portland cement?

Regards
Bart

[Johnny the oven man]

Re: Insulation Efficiency

I am starting to gather materials for my build. My supplier has some 4" wool blanket that is good to 1200 degrees that he will let go for $2/ft^2. My only concern is that this is getting a little too close for comfort in regards to heat. I am just not sure if this is the max temp rating or the working temp rating. With the "mother of all fires" going, how hot would you anticipate the outter portion of the dome will get ( I should mention that I will be casting a dome 3" thick)? I guess a return call is in order! I didn't want to pass it up for that price.

He is also trying to push me on a vermic/portland refractory premix that they sell relativly cheap:

1900 deg-F Insulating Castable (over dome) 30lb/ft^3, so 1 bag covers 1 2/3 cf -50# bag @ $9.00 ea ( I estimate I will need 4 bags to get around 2.5" thick)

Your thoughts??

You will most likely find, if its ceramic fibre blanket it is rated at 1260C not F, so you are safe. You can hold a blow torch on one side of 4" and not feel the heat through it. Melting point is 1700c.

[backinoz]

Re: Insulation Efficiency

Snow is an insulator but I wouldn't suggest it for this application.http://www.fornobravo.com/forum/imag...lies/smile.gif

[DimTex]

Re: Insulation Efficiency

I laugh along with philiph4 because with my oven just a few months old I find every excuse to fire it up. I bought 2 cords of pecan firewood (1 to use, 1 to age) and I try and fire it up every Friday night. With teens in the house pizza is always a slam dunk, what ever will I do when they go to college? Well that's still 20 months away...

[philiph4@ameritech.net]

Re: Insulation Efficiency

I haven't posted since I finished my oven so I wanted to give you an update. I ended up using 2 inches of 8# Kaowool covered by 3 inches of vercrete then a stucco finish. Although I don't have a thermometer I can get the dome to go clear in about an hour so it has to be at least 700 degrees F. When I touch the outside of the oven I can't detect any heat. We had our first snow (just a dusting), however, and after about an hour at full heat all the snow melted so it must be getting a little warmer on the exterior. I am having a blast with this oven; pizza galore, lots of fresh baked bread and I even made the Thanksgiving bird. We've had some great parties and my friends love it too. The only problem is keeping my weight down. Oh well, you only live once!

Happy Holidays!

Phil

[jbriggs]

Re: Insulation Efficiency

I am starting to gather materials for my build. My supplier has some 4" wool blanket that is good to 1200 degrees that he will let go for $2/ft^2. My only concern is that this is getting a little too close for comfort in regards to heat. I am just not sure if this is the max temp rating or the working temp rating. With the "mother of all fires" going, how hot would you anticipate the outter portion of the dome will get ( I should mention that I will be casting a dome 3" thick)? I guess a return call is in order! I didn't want to pass it up for that price.

He is also trying to push me on a vermic/portland refractory premix that they sell relativly cheap:

1900 deg-F Insulating Castable (over dome) 30lb/ft^3, so 1 bag covers 1 2/3 cf -50# bag @ $9.00 ea ( I estimate I will need 4 bags to get around 2.5" thick)

Your thoughts??

[havefun]

Re: Insulation Efficiency

Hi Mark thx for your reply u not confused me just reinforced what i was thinking to do accually i just got hold of some off cuts from a mate builder here they are called peltex its a 4 inch insulation some are 5 with fairly thickish aly tape like linning on one side n about 3/8 ply on the other n i was about to cut it to shape over the stone door but overlap it about couple of inches,

then was thinking to use a 4x2 timber between the two shelter supporting timbers so as it presses hard against the door hopefully it will push the insulation into shape n give me a good seal

so now i will try it just have to shape it round the door handle as i don't fancy the handle been secured on the ply, as the door is at a small angle the more i push the timber down the harder it will push the door against the oven opening (that is also made from stone) overlaped with clay mixure if i still lose heat i'll try some rubber on the overlapping peltex as its far less hot there
next i got to work out how long to get the oven hot i think now am getting it hotter than i need to n i really hate waste even the timber is free CO2 its NOT!

[ThisOldGarageNJ]

Re: Insulation Efficiency

Havefun,
I have a wooden door, 2 inch hard maple with 2 pieces of 18 gauge sheetmetal on the side that faces the oven.. I also had to wrap the edges with aluminum foil otherwise they started burning.. I will change the foil to aluminum angle iron, You can also make a door out of FB Board, Some have cast theirs out of refractory cement.. I thought about the synthetic rope seal as well, but found with my wooden door I was able to shape it to an almost exact fit.. and had very little heat loss, I cooked a 13 lb turkey in a little over an hour and a half... Cant beat that with a stick... The wood door can also be soaked in water to keep it from burning and the steam released into the oven is very good for baking bread ( I believe it helps the crust) My next door, will not be hard maple though as it is very dense and doesnt allow it to soak up much water... Hope I helped you and not confused you
Cheers
Mark

[havefun]

Re: Insulation Efficiency

guys the overall thickness of my dome is just over 6 inches nearly 7 on the top after cooking that is mainly lamb n potatos rubbed in foil burried under the ash that is after at least an hour burning n maybe up to 2 hours cooking the top of the dome is hardly warm the sides are fairly hotish i used alltogether two bags of vermiculite but of course i used a lot more on the top n half the bag was used under the bricks i feel am using more heat than i need as after not to waste heat i dry logs in the oven n it keeps the heat till at least 18 hours later also it fires almost as good without FLUE finally what is the best material to use on the 35mm stone door as that get HOT n what's best to use for sealing the door without having to use clay everytime i cook i used vermiculite on the door but eventually it came off CAN I USE SYNTHETIC ASBESTOS ROPE AS USED ON BOILERS TO SEAL THE DOOR TO THE OVEN? were the door fits its also cut from the same thickness paving stone just need to be able to seal the heat in without using plaster or clay everytime but what material can i use?

[ThisOldGarageNJ]

Re: Insulation Efficiency

having too much insulation is like having too much money... is that possible ??

It sounds like you'll be fine

Cheers
Mark

[philiph4@ameritech.net]

Re: Insulation Efficiency

I had 1 box of 50 sf of koawool and got 2 inches over my dome. I fired the oven and it got to at least 700 degrees because the dome went clear. Without a door the oven was still quite warm in the morning. The top of the dome was warm but not hot. I am going to cover the dome this weekend with vermiculite cement (Igloo design). But I am feeling pretty good that I already have enough insulation and the vercrete will be a bonus.

Phil

[DimTex]

Re: Insulation Efficiency

Yes, I did

[Doodney]

Re: Insulation Efficiency

I purchased 3 boxes of the FB blanket and it was more than enough to swath the entire dome and entry of my 36 inch oven in four layers of the stuff with some leftover. After a few firings where the dome was well over 900 degrees I can safely say the top and back of the stucco dome conducted barely any heat from the heat inside the dome. The stucco dome felt about the same as the ambient air temperatures outside. After wrapping the dome and blanket with chicken wire I can say my first ever attempt at stucco came out pretty good and it was quite easy. I don't know if I had tried the vermiculite path whether I would have had the same results.

say, how many inches of FB blancket did you end up with on your 36"?
Since you used 3 boxes did you get 4" of insulation out of it?