homemade block arch insulation

[tcross]

I made a block arch last year and it worked pretty well! I did not use any fire brick. I insulated my blocks with fiberglass insulation shoved down the open holes! it seemed to work and keep the outside of the blocks warm, but certainly not hot! this year, I am getting a nice 4x4 flat pan with dividers and plan on building my block arch to accommodate that size! I am wondering if having my block arch this big if the heat inside will be more intense! last years was 1/2 the size! I am thinking of pouring sand in the holes as insulation and mortaring the joints on the block! I think the sand would insulate better then fiberglass but i'm still skeptical! Last year I only had one cinderblock crack... and I think it was an older one? I know I should probably get firebricks but my budget is running out! would the cinder blocks withstand the heat if insulated with sand inside them? any opinions?

[NH/Pete]

With my block arch I filled the holes with sand. I also lined the inside with 1/8" scrap steel.
No other insulation. I still had three cracker cinder blocks. The outside of the arch got warm not hot.
Insulation and fire brick would be the way to save the blocks.

Then again cinder blocks are cheep.

[northernlite]

Used just the same cinder block for 3 years, fell apart finally. New design for firebox on existing poured slab, block filled with sand and lined with firebrick. Going to have new pan made to fit box. It will be a flat pan 4'x3' with 2 raised flues and spigot. We'll see how that works . Made 4.7 gal this yesr

[Stoneduster]

The heat will break down the Portland cement in the blocks, regardless of whether there is insulation in the cells or not.

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[NhShaun]

I lined the inside of my 2x6 block arch with 1 inch ceramic insulation. Put firebrick on top of that in the firebox. Didn't have any cracked blocks and it kept most of the heat in, fired pretty efficient for block arch I'd say. The ceramic insulation held up great besides being covered with ash.i Isn't too pricey either if you buy a roll. Made just over 10Gal this past season.

[ScottyWelden]

My design was similar: two layer, U-shaped base with grate on top. On top of that, inside walls of sheet metal, 2" high-temp insulation outside that, cinder blocks for the outer layer. With two 15x20" warming pans, I was boiling off up to 7 gallons per hour! And the cinder blocks were barely warm.

[canadian_diesel1964]

Used firebricks are available, cheap and work great!