[wireb]

Working on a firebox for a small boiler and the plans call out for asbestos sheet to line it. Not real keen on lung cancer + cannot find a source for it anymore.

What is a modern replacement for 1/8" thick flat asbestos sheeting? (used to protect the aluminum firebox from the propane burners) Is there any sort of kiln brick that would work (I think I can easily modify the plans to use 1/4" liners if needed)

[RomanLini]

You could maybe use fibreglass mat, it comes in a chopped strand mat that is about 1/8" thick. Although fibreglass has it's own health issues. It's available from big hardware stores for general fibreglassing use.

A much nicer material is "perlite" it's like rice crispies but very heat proof (enough to be used in kilns). You can buy it from nurseries quite cheaply as it's a soil additive. I have seen perlite used with a small percentage of mortar used to hold it together to make a solid aggregate heat proof material. However as the perlite pellets are about 1/4" in size this might be too big for your needs. The good point is that you can apply it to the walls of the box with a spatula and it sets like a layer of heatproof concrete.

There's probably some threads about perlite heatproofing in the "Casting Metals" section of the forum.

[DMF_TomB]

i believe you are looking for ceramic fiber blanket or paper

Ceramic Fiber paper

they also sell rigiderizer which is a liquid that when painted on soft ceramic fiber blanket makes it harder and more durable. there many suppliers

Ceramic Blanket Forge and Furnace Insulation

sells small quantities for hobby foundry casting

warning most ceramics exposed to high heat form compounds that are not good to breath. not as bad as asbestos but silicosis is a bad condition to get too.

[wireb]

Thanks for the links. Bummer they only stock the 1" thickness. But the comment about coating the fibers to make them stiff got me thinking. I have a tub of 2700deg refractory adhesive (for sealing metal flue pipes to brick) that can be applied up to 1/8" thick per the label. I am going to try and coat the inside of the firebox with this and see how it works. This stuff has a bunch of course material in it and fiber reinforcement so hopping will will work for the indirect flames off the burner in this little boiler.

[Autonow]

Thanks for the links. Bummer they only stock the 1" thickness. But the comment about coating the fibers to make them stiff got me thinking. I have a tub of 2700deg refractory adhesive (for sealing metal flue pipes to brick) that can be applied up to 1/8" thick per the label. I am going to try and coat the inside of the firebox with this and see how it works. This stuff has a bunch of course material in it and fiber reinforcement so hopping will will work for the indirect flames off the burner in this little boiler.

While not cheap McMaster Carr has Ceramic fiber blanket.
The big supplied is western Industrial Ceramics

Any By the way Rigidizer is just colloidal silica avail from a industrial chemical supply house (way cheaper)
Depending on the thickness you need, 6" for a firebox in the 1400 to 1800 degree range. the best method is to use the equivalent of "pyroblock" Ceramic fiber strips stood on edge and compressed together. Unlike insulating a house you want to firmly compress the fiber then rigidize the surface for a firebox. But in most small boiler design there is really very little insulation. Most designs use a fire tube boiler design where the firebox heats the water cooled fire tube.

[Joe S.]

Thanks for the links. Bummer they only stock the 1" thickness. But the comment about coating the fibers to make them stiff got me thinking. I have a tub of 2700deg refractory adhesive (for sealing metal flue pipes to brick) that can be applied up to 1/8" thick per the label. I am going to try and coat the inside of the firebox with this and see how it works. This stuff has a bunch of course material in it and fiber reinforcement so hoping it will work for the indirect flames off the burner in this little boiler.

The refractory adhesive will likely take the heat but it offers little insulation to the aluminum firebox. Keep in mind aluminum is liquid at about 1500F and mush at much lower temps. I would laminate a layer of fiberglass between the outside wall and a sheet metal (steel) inner wall, which you could coat with refractory.

[Autonow]

Besides Ceramic "blanket" there is also ceramic Paper. Paper comes in 1/16 1/8 and 1/4" thicknesses It is higher density usually about 12lb/cuft. Still rated above 2200 deg F. Western ind Ceramics Western Industrial Ceramics | High Temperature Ceramic Insulation sells Fiberfrax paper Fiberfrax Refractory Ceramic Fiber - Fiberfrax High Temperature Insulation. For small pieces, McMaster Carries it in strips. Just have to know what to look for. try 87575K89.

[snoeproe]

I used ceramic wool matting around the wall thimble for the selkirk flue on the wood pellet stove i put in my house. Nice stuff to work with.