Is this a more modern way of building the insulated slab?

[angelboy]

I was going to go with a 3.5" reinforced concrete slab, 100mm vermiculite insulation (with portland cement) and 50mm firebrick but having watched this would it be better to go for 40-50mm of Calcium Silicate Boards, 25mm of refactory castable concrete then the 50mm firebrick?


Edit: Sorry for the link - I'll be more careful in future.

[fox]

Lots of different ways, I use 100mm concrete slab, 100mm ceramic board and 70mm fire brick.
The bricks are standard size where I live and lay directly on top of the insulating board.
A lot will depend on your location and availability of materials …..

[david s]

There are disadvantages using castable refractory under the brick floor to increase thermal mass. Firstly it is tricky stuff to work with, quite expensive and adds water to an area that you want dry. Excess water in the castable should be allowed to dry thoroughly before laying the floor bricks over it, otherwise it would trap the moisture in. Ben's solution to prevent the calcium silicate board from sucking water from the castable also leaves a permanent moisture barrier that can cause problems in not allowing the castable to dry easily from the underside. Also later, once the oven has been completed dried and fired, should the entry of water and its removal be required, the impervious foil barrier will slow down water removal. Moisture in the under floor insulation drastically reduces its capacity to insulate because water is a conductor. Eliminating this under-floor moisture takes many firings. Providing an easy pathway for its exit is well worth it.

Far better to access, if possible, some thicker firebricks. They come in all kinds of shapes and sizes, but if they are a standard 9 x 4 x 3 inch size then they can simply be turned on their sides to get a thicker floor. While a thicker floor will hold more heat, also the longer it will take to heat up (more time more fuel). Generally a 2" thick floor is considered adequate unless you want to bake multiple batches of bread.

[Hamilton]

Who is Ben?
I didn't see his response in this post.

[Pizzarotic]

Who is Ben?
I didn't see his response in this post.

Ben Guilford owner of The Melbourne Fire Brick Company. They make what is arguably the best kit oven in Australia. Probably one of the most expensive as well but you do get what you pay for, their quality is exceptional.

[Pizzarotic]

I was going to go with a 3.5" reinforced concrete slab, 100mm vermiculite insulation (with portland cement) and 50mm firebrick but having watched this would it be better to go for 40-50mm of Calcium Silicate Boards, 25mm of refactory castable concrete then the 50mm firebrick?

Solid build plan. The calcium silicate board is always going to outperform the vermiculite but at significantly more cost.

The 25mm of refactory castable concrete will be very beneficial if you are wanting to achieve long residential heat cooking which is what the Melbourne fire company ovens do very well.

[angelboy]

I think I'll go with 50mm calcium silicate boards and a 75mm firebrick for the oven floor.

[fox]

50mm would be the recommended minimum but if you want to retain heat for several days I would go for 75-100mm.
I regularly read about how much cheaper vermiculite is compared to ceramic fibre board but where I live I dont think that is the case at all!
Apart from any cost difference you also have the hassle of mixing the vermiculite and waiting for maybe two weeks fot it to dry!