CaSi Board Necessity

[tufenk]

I am installing my cooking floor onto my 4.5-inch concrete hearth at the moment and was wondering how necessary a CaSi insulating board would be. I am over budget already and the CaSi board is rather expensive. What are the downsides of not adding that extra layer of insulation and will it have negative impacts on my oven? I want to note that my firebricks are heavy/super duty firebricks, which from what I have researched means they retain heat even more so than medium duty firebricks which means maybe another insulating layer would not be as necessary. Thanks, everyone.

[UtahBeehiver]

You need to insulate under the floor and the dome edge or the concrete hearth will act as heat sink and the oven will not perform very well. The oven floor will not retain heat.

CaSi is the most effective insulation but you could install a 5 to 1 p/vcrete a min of 4" thick to equal 2" of CaSi board as a budget option. There are plenty of builders and thread regarding p/vcrete.

DO NOT skip the floor and dome insulation.

[fox]

Ok well what will happen if you dont insulate under the floor, the heat from the fire will start to travel down through the bricks and then start to penetrate down into the concrete base under the bricks.
The whole mass of the concrete will start to absorb the heat from the fire until the whole base is finally saturated with heat, this might take many hours while all the time stealing heat fro the fire and stopping the heat spreading out and up the walls of the dome!
If you do use insulation ( and plenty of it) the fire will heat the bricks and then hit the insulation stopping it from going any further but reflecting the heat back up into the bricks making them much hotter much faster and allowing the fire to spread the heat out and up the walls.
So in effect you will have a much faster heat up time, hotter bricks and burn a fraction of the fuel.

[tufenk]

You need to insulate under the floor and the dome edge or the concrete hearth will act as heat sink and the oven will not perform very well. The oven floor will not retain heat.

CaSi is the most effective insulation but you could install a 5 to 1 p/vcrete a min of 4" thick to equal 2" of CaSi board as a budget option. There are plenty of builders and thread regarding p/vcrete.

DO NOT skip the floor and dome insulation.

Do you have any suggestions for places to purchase CaSi/AlSi board. What I'm seeing online is ~50$ for 12"x12" pieces with 1" thickness. Which is absurd. I should have poured the vermicrete hearth in hindsight.

[UtahBeehiver]

So why can't you pour a v/pcrete layer on top of concrete hearth? Yes CaSi is expensive but it is what it is. Most refractory supply shops carry CaSi (You wont't find this at HD or big box stores) Trade names would be ThermoGold 1200 (water resistant), IsoBloc, You just have to call around, Distribution International is a solid supplier but not the cheapest. Before you purchase any CaSi you should post the specs on the blog for review, not all CaSi are suitable. If you can install CaSi, why can't you install p/vcrete? PS If you have not already downloaded, studied and reviewed the free eplans from Forno Bravo, you should.

[tufenk]

So why can't you pour a v/pcrete layer on top of concrete hearth? Yes CaSi is expensive but it is what it is. Most refractory supply shops carry CaSi (You wont't find this at HD or big box stores) Trade names would be ThermoGold 1200 (water resistant), IsoBloc, You just have to call around, Distribution International is a solid supplier but not the cheapest. Before you purchase any CaSi you should post the specs on the blog for review, not all CaSi are suitable. If you can install CaSi, why can't you install p/vcrete? PS If you have not already downloaded, studied and reviewed the free eplans from Forno Bravo, you should.

Thanks for the response. I have reviewed the Forno Bravo plans. The reason I can install CaSi board and not P/Vcrete is primarily due to the final height of the oven. I am comfortable raising the oven 2 more inches but raising it 4 more inches will make my oven too tall. Both my dad and I are 6' 2" so I did 5 courses of cinderblocks for the base. With the ~4.5 inches of concrete hearth and the additional two inches of the firebricks makes the oven 46.5" tall without the insulating layer. Adding much more height would make the oven obnoxious to use I fear.

I'm calling around and the quotes I'm getting for 4'x4' CaSi are just too much for what I feel comfortable with at the moment. Would 3" p/vcrete be doable?

[fox]

I think I have already explained why we use insulation and the effects of using too little but, there is nothing stopping you using less than the recommended minimum….it just means your oven wont work as well!
Have you looked for ceramic fibre board, it has slightly better insulation than Calcium silicate board but may be even more expensive where you live?