Recycled Insulation, any thoughts or warnings?

[Thailandnotes]

High temperature insulation here in Thailand is very expensive. A roll of blanket insulation was 300 dollars about five or six times the price in the states. I toyed with using rice husk ash as that is what small hibachi type ovens here are insulated with. Then I bumped into a Thai guy who has a factory making roof tiles. He was upgrading his kilns and replacing the insulation bricks inside. He gave me a pick up load of white insulation. They measure 8 by 12 inches and are 5 inches thick. They are relatively soft. Some are slightly chipped or pocked.

I can cut them neatly in half by putting them in a frame and running a serrated bread knife along them.

I'm worried about the weight of the oven making them sag, because they are not one continuous board.

The other question I have is what is the best dry mix to lay down on top so that the oven floor is level.

Thanks for any feedback.

[brickie in oz]

Re: Recycled Insulation, any thoughts or warnings?

I'm worried about the weight of the oven making them sag, because they are not one continuous board.

It sounds like ceramic fibre insulation which is no good for underneath the oven as it will compress and be useless.

[TropicalCoasting]

Re: Recycled Insulation, any thoughts or warnings?

Make sure its not got asbestos in it.

[Thailandnotes]

Re: Recycled Insulation, any thoughts or warnings?

I thought about that. The guy I got them from said they did not contain asbestos, but I don't know him or anything about him, and it seems online that there is no way to tell. I have a hard time imagining them imploding under the weight, but I have no way to really know. Am thinking about encasing them somehow or just going with vermiculite.

[david s]

Re: Recycled Insulation, any thoughts or warnings?

Be careful, while ceramic fibre blanket does not contain asbestos it is classified as a class 2 carcinogen (unless it is the water soluble type, which is unlikely) that means that no cases of cancer have been reported in humans (yet), but tumours have been found in rats used for testing. Make sure you wear a mask when handling or cutting it. The dangerous part is inhaling the fibres rather than ingesting them.

[ATK406]

Re: Recycled Insulation, any thoughts or warnings?

Sounds like you have a good find there. The size is ideal. I would be careful handling them and wear PPE when cutting them etc. The compressive strength is hard to judge without seeing them for myself.

It sounds like you've got an insulating brick similar to what I used under my hearth. The weight of the oven is widely distributed across the surface of the hearth floor and these bricks will probably work fine as long as the hearth slab beneath them is solid. Mine were only 2.5" thick and I wish I had more insulation under my oven...so I'm envious. If you have any suspicion that these bricks are not strong enough to support the weight of the FB above you could conduct a simple test. Stack a load of FB on top of one of these insulating bricks 10 or 12 should be enough and see if there is any sign that the insulating brick is collapsing. You could even take measurements if you want to get scientific about it.

My insulating bricks were brand new (and expensive) so when I laid them down on the hearth slab they were already level. When I laid my Firebrick on top of that (I used large 12" x 24" FB) I found that I needed to make a few adjustments to get my floor even. I simply lifted the FB and scraped the surface of the insulating brick with a sharp edge until I was able to get the FB in the position that I wanted. I'm sure that you could use a mixture of clean sand and fireclay to level the floor as described in the FB plans - that's probably safer too.

I wouldn't worry too much about the chemical composition (asbestos or whatever) because your insulation layer will be completely encapsulated and will not come into contact with the food (as long as it has not been saturated with something or give off any suspicious odors - you should be fine).

Regards,
AT

[Thailandnotes]

Re: Recycled Insulation, any thoughts or warnings?

Not knowing what they are or what they were exposed to now has me paranoid. After all, they were inside a kiln where roof tiles were being fired and those tiles were glazed.

Encapsulating them seems to be the way to go, but I'm thinking that might take more refractory mortar and time and design than it's worth.

[ATK406]

Re: Recycled Insulation, any thoughts or warnings?

IMHO encapsulating the insulating brick in a thin layer of refractory mortar would be relatively inexpensive and easy to do.

[david s]

Re: Recycled Insulation, any thoughts or warnings?

My apologies. On reading your first post it is clear that what you have are insulating firebricks not blanket. The bricks are ideal for insulating under the floor, they will have plenty of compressive strength,but you will need dense firebricks for the floor itself. I wouldn't hesitate to use them as underfloor insulation and sure they'll be quite safe. Blanket is another story.
For a leveler try a 50/50 dry mix of sand and fireclay.Then lay wet floor bricks over it and let the whole lot dry.

[Thailandnotes]

Re: Recycled Insulation, any thoughts or warnings?

IMHO encapsulating the insulating brick in a thin layer of refractory mortar would be relatively inexpensive and easy to do.

OK. I cut the insulation brick in half. A half of one is about 3.5 inches thick. I laid out a firebrick frame and laid the insulating bricks inside. The bricks are 1/2 an inch higher than the insulation. Can you pour a 1/2 inch layer of concrete without it cracking (wire mesh?)?

[ATK406]

Re: Recycled Insulation, any thoughts or warnings?

OK. I cut the insulation brick in half. A half of one is about 3.5 inches thick. I laid out a firebrick frame and laid the insulating bricks inside. The bricks are 1/2 an inch higher than the insulation. Can you pour a 1/2 inch layer of concrete without it cracking (wire mesh?)?

When you say "concrete" I hope you are referring to the refractory homebrew (a 3:1:1:1 mix of sand, fire clay, lime and Portland cement frequently recommended on this site) or one of the commercially available refractory mortar or cement mixes. Standard concrete will not hold up to the heat (it will breakdown when temperatures exceed 600F).

The homebrew and mortar mixes are intended for use between bricks and are not generally used at thicknesses greater than 1/2" where tensile loading will take place. However the tensile limitations of this material will not be a factor in your application because your "concrete"/mortar layer will be under compression (trapped between your insulation and Firebrick hearth).

If I were you, I would make your "concrete"/mortar layer approximately 3/8" thick leaving room for some sand and fireclay underneath your firebrick to help in leveling the hearth (reference David's post above).

What size are your firebricks? Reading your post above it sounds like you have some very large bricks (1/2" thicker than your 3.5" insulation) or are you laying your FB on their sides? Also are you planning to build your dome on top of the hearth floor or will the hearth bricks be cut to fit inside your dome? Maybe some pictures would help.

Regards,
AT

[Thailandnotes]

Re: Recycled Insulation, any thoughts or warnings?

These firebricks are slightly larger than what you would find in the states. I surrounded the insulation blocks with the bricks, then covered the insulation blocks with a thin layer of sand to fill in nicks and slots. Then I used a 6/1 perlite/refractory cement mix to cover that.

I have a hard time believing this is sealing anything, but I'm a rookie.

[ATK406]

Re: Recycled Insulation, any thoughts or warnings?

Hey, we were all rookies once and even "experts" make mistakes (know anybody on Wall Street?). With what you've done so far I think you're golden.

Given the relatively uneven surface of the perlcrete insulation, I would recommend a 3-5 mm layer of sand to make life a little easier when laying your hearth bricks (many here would even recommend a 50/50 mix of sand and clay - I think the clay is supposed to make it easier to level).

Do you plan to build your dome on top of the hearth or are you going to cut your hearth bricks to fit inside the dome?

Looking forward to watching the rest of your build and I'm curious about the Thai recipes you have in store for us.

Good Luck,
AT

[Thailandnotes]

Re: Recycled Insulation, any thoughts or warnings?

Ok, after laying the hearth, I'm on to beginning an arched opening and the dome. When I mixed the refractory cement with water and used it to test with four or five bricks, after it dried, I could pull the bricks apart and crush the dried cement back into a powder. Not good.

I mixed about 25 % Portland and 75 % refractory and that produced what I was hoping for, but before I go forward, I would like to read up on how refractory cement should behave, what adding to it might do down the line. I've looked on the internet and googled this site, but I'm hoping someone can provide a link so I can cut quick to the chase.

Comments and suggestions also appreciated.

[david s]

Re: Recycled Insulation, any thoughts or warnings?

OK. I cut the insulation brick in half. A half of one is about 3.5 inches thick. I laid out a firebrick frame and laid the insulating bricks inside. The bricks are 1/2 an inch higher than the insulation. Can you pour a 1/2 inch layer of concrete without it cracking (wire mesh?)?

I'd be pouring a 1/2" vermicrete slab over the insulating bricks, then if it is uneven lay a thin bed of 50/50 fireclay/sand over it before placing the firebrick floor.

Oops, sorry. I see you've already done it.