Insulation Efficiency

[Spunkoid]

Re: Insulation Efficiency

What started me down the path of building a forno was a nostalgic thought of my Grandmothers clay oven on her homestead. Clay and straw or clay and sawdust have been proven over time as traditional building materials. I am not sure if they have the same insulative factor as cement and vermiculite but are probably excellent alternatives. If you have the space, just make the insulative layer thicker. One question though, will the material weaken as the the straw burns out?
I would stay well away from styrofoam as there would be chemical residue coming off of it for a long time. Keep in mind you are using this for food you are eating.....

[trockyh]

Re: Insulation Efficiency

We use wood shavings in our chicken coop. They are much larger than saw dust and would probably work well and they are inexpensive. $5 per bale.

Tom

[Johnny the oven man]

Re: Insulation Efficiency

My only concern is, you wouldnt really be able to get up to a temperature to burn out the foam or woodchips without actually firing the bricks above say, 1000c+, which is what the brick manufacturers fire at.

[david s]

Re: Insulation Efficiency

Pottery kiln builders sometimes use sawdust and clay mixed together as an insulating layer. It is highly unlikely that the sawdust will burn away,rather it will just dry and leave a lightweight pocket containing air. Clay is a much better insulator than cement (ever been in a mud brick house in mid summer? You'd swear it was aircond.) Clay is dense though and I suspect the mix would not be near as effective as perlite or vermiculite. Another material that is traditionally used is manure. I think because it contains a lot of undigested material (I'm thinking horse manure here) If you used a lot of chopped straw and mixed a minimal amount of clay and manure (just enough to make it hold together) you'd get a pretty lightweight and insulative mix. Allow it to dry really well before curing and stucco.

[wemme]

Re: Insulation Efficiency

kiko denzer has written on his blog he had better results in the longer term with saw dust than long straw after the straw burnt out the clay began to compact causing a reduction in it's insulating qualities.
Regards
Bart

[jbriggs]

Re: Insulation Efficiency

Talking to a ceramic engineer of 30 years, who is now in sales for a well know refractory supplier, I have worn him out with questions regarding every phase of the oven building. He told me that going with #8 Kaowool is really a waste of $$ seeing that #6 and #8 both have the same insulating properties until about the 1700F mark, at which time the #8 will continue to hold its own, but the #6 falls off slightly. Seeing that the #8 cost a great deal more, it is a lot cheaper to use two (or more) layers of the 1" #6 than to go with #8.

He has also sold me on a lightweight premixed 1900 deg-F Insulating Castable to render over the dome, It is 30 lb/ft^3 density and sold in 50# bags, @ $9.00 ea. Bang for the buck her is that this will cost less than $30 to insulate the dome, and on top of that I will still use 1 layer of #6 Kaowool.

Guys like this are good to talk to and have been in the industry forever and really know what works and what is a waste. They use these products day in/day out in high temp furnaces and kilns, so they see a lot of this as overkill when it comes to only 1000-F that we see in a typical firing.

[tony007]

Re: Insulation Efficiency

First I want to thank everyone for providing such great information that helped me build my first oven. Also the folks in Florida for the help locating suppliers. I spent much time reading this forum and finally, voil? - completed the dome last week.

I'm at the point of insulating the dome with 1" blanket (Superwool), I'm concerned of placing the vermiculite/cement mixture directly over the insulating blanket (and chicken wire).
Could that compress the blanket so that it loses it's insulating properties?
What do yo think of these options:
> Aluminum foil or some other material between the blanket and vermiculite/cement?
> Using stucco metal lath instead of chicken wire to provide gap/support?

[david s]

Re: Insulation Efficiency

No the blanket is fairly firm and does not compress as the vermicrete is really light. Lots of people have followed this method without compressing the blanket. Some people use a foil layer, there are pros and cons for doing this, eg prevention of moisture loss into the blanket. This creates problems later by locking in moisture below the foil. I think (others may disagree) it's better to skip the foil. If you get the consistency of the vermicrete right it just sits there and dries without disturbance to the blanket.

[dmun]

Re: Insulation Efficiency

Aluminum foil or some other material between the blanket and vermiculite/cement?

The aluminum foil idea has been debunked again and again. There's no use for it in oven building except to create a non-adhesion layer between different masonry parts, for a slip plane. Since it decays in the presence of the corrosive mortar, it doesn't have any heat reflective properties.

[wemme]

Re: Insulation Efficiency

Foil also stops Moisture from passing out, causing condensation between the thermal and insulating layer which can cause clay ovens to collapse and can't be good for brick/cast ovens either.

[gdest]

Re: Insulation Efficiency

I am planning on putting 4" of perlite concrete under my oven to insulate the floor. Can anyone tell me if it is necessary to install some wire mesh in this concrete?
My first thought is no since this slab will only be in compression and by adding wire, I might be lowering the insulating properties.

[ThisOldGarageNJ]

Re: Insulation Efficiency

G,
Putting anything in yout perlite is not necessary, The compression strength is great enough to hold your oven,, You should certainly put rebar in the slab that holds your perlite....

Cheers
Mark

[gdest]

Re: Insulation Efficiency

James
Need some advice here!

I purchased two gallons of what Boral Brick told me was fire clay, even though it stated on the bucket "mortar". I called up the manufacturer and found out it was in fact high temp mortar.
Now lacking any fire clay can I do any of the following:

1. Just install a leveling course of sand down under the floor?
2. Mix some of the sand with the mortar and use that as leveling
3. Try to find a fire clay and how much? I am buiding a 42" ID oven.

My first thought is just to use the sand for leveling. I don't know what value the fire clay adds when you mix it with the sand and water to place it under the floor.

Thanks in advance for your advice

Gary

[wlively]

Re: Insulation Efficiency

I don't know what mortar you are using, but if it a very fine texture then I don't see a problem with using it wet or dry. You are just trying to bed the bricks evenly.

The floor has been done wet or dry by many. Pick either method you prefer. Myself, I decided to trowel a wet bed for my floor bricks. Worked fine, is still perfectly flat and looks as good as the day it was put down.

[gdest]

Re: Insulation Efficiency

It is a pre-mixed wet mortar. But what I was really asking was all the plans I have seen state that you mix fire clay with fine sand 50/50 wet it and then trowel in on the bottom to get a level surface. What does adding fire clay to the sand do for you?

Thanks

Gary