PS If I made my J-Tube out of the fire brick from Home Depot the 7lb bricks about how long should the J-tube last?
Refractory Materials Supply !
If you go with the
'come up to temperature' with dirty smoke from your chimney l-o-n-g-e-r, and because those bricks are doing exactly what they are made to do, hold heat
and radiate that heat out slowly, your hotter combustion core will thermo-syphon heat energy from the core and from the Cob thermal mass longer- after
your fire is out, negating a big plus of the J-tube Style rocket mass heater ! For the good of the Craft ! Big AL !
Your other option is to acquire a cast refractory core which has been made with a commercial insulative, but strong formula. We vibrate the casting and then kiln the result. The feed tube is steel and the heat riser is vermiculite board surrounded by loose perlite. We also have plans and kits for mass heaters which will be up and warming you a lot quicker than a huge mass of cob which has to dry out first. You won't have to rebuild it next year.
thomas rubino wrote:David; ; Components of cast cores & risers are one 50#sack fireclay + one 2 cubic foot bag perlite + fiberglass as a binder and as much refractory cement as you can afford , I used 2 gal tub between core & riser. I would have 4 bags of fireclay on hand and 2 four foot bags of perlite, I used bagged concrete fiberglass as my binder maybe 1/2 bag for core less for the riser. I used an 8" sonitube as my inner form on the riser with a 16 gal metal barrel as the outer form. The core is formed with plywood & hardy board. When i build my next cast core & riser I will also have a bottle of sodium silicate (waterglass) on hand and paint all fire surfaces inside the core & the top of the riser just before firing to create a harder refractory surface.
I was wondering if the fireclay is the same as the refractory cement, or if they are two different things.
Sodium silicate reminds me of the lime water I used to fireproof the wood in our chicken coop. Could I use that to fireproof the the inside instead of sodium silicate?
Perlite seems to be the better choice over vermiculite, but I still don't know the reason why.
One more thing, could I also use rockwool in place of the fiberglass? Which is better, and why.
the best, rather it is because it expands when heated, and contracts the least amount when cooled !
Usually Refractory cement is called 'hard' which means it expands and contracts little, but this can cause the brick it is bound to to chip crack, or break in half !
Here is where it gets tricky, Some people dip their bricks in water for about a 5 sec. count and then dip them in a clay slip, and using the clay slip as a sealer between
clean sharp bricks, lay up their burn tunnel with out any Refractory cement to mortar at all. once ' layed up' this method seals out air gaps and is quite effective in building
both the Burn Tunnel and Heat Riser during your outdoor experimentation phase !
During the actual indoor build, you can still build a Burn Tunnel this way as it will be wrapped in insulation and protected from being jared by the setting of the barrel over
its top !
However, the Heat Riser, which is subject to being jarred or moved by the Placement of the Barrel needs ether a clay and sand mortar to lock the bricks of the Heat Riser
into one solid unit , or the use or a Refractory Cement! - Here again you may find that the Clay and Sand Mortar is more forgiving than the Refractory Cement
The use of Sodium Silicate is an option, rather than relying on a clay slip and Perlite mixture, I have been told that the fine dust of the perlite needs to be screened out
- otherwise the fine dust combines with the water glass and becomes very much like glue !
Lime water retards the ignition point of fire, making it safe to hang heat lamps in close proximity, water glass will allow a product that is very much like rice cakes to stick
to itself, and create a mass of Perlite that will be more insulating, and more highly refractory (two separate things ) than just a mixture of the cheaper clay slip and Perlite !
If Sodium Silicate with Perlite is better than Clay Slip and Perlite, (probably, but I have not seen figures !) Then because the vermiculite will need to take up more Clay Slip
to bind to itself, it is inferior to ether of the perlite mixtures !
Rock wool, also sold under the name Roxul, (SP) is cheaper and possibly superior to ether perlite, or vermiculite, it is generally held in place with a wrap of chicken wire, it
does take a certain amount of faith to believe that the chicken wire will last as long as the barrel, so far @ at least 4 + years, it seems likely to do so !
I blame the advertising agency connected with the selling of a specific type of 'pink' fiberglass with convincing must of the people in the U.S. that if it comes as a 'Batt' or
on a 'roll', that the product is fiberglass, in fact you do not want the fiber glass you want only the 'rock wool' Good luck Big AL !