Furnace floor insulation

[david s]

The floor bricks are better laid loose so they can expand and contract freely and independently. This also makes their removal and replacement easier should that need to be done. A thin dry mix of sand and powdered clay can be used as a leveller layer if the firebricks are of an uneven height.

[bencuch]

Hi David s,

I decided to put a layer of heat-resistant concrete (4 cm) under the fireclay brick to keep the furnace hot longer.
Can I pour refractory concrete directly on SUPERIZOL (doesn't matter if they stick together)
Then stick the fireclay floor brick on the refractory concrete or just lay it loosely.

Well thank you.

[david s]

Vermiculite concrete ratio 1 to 4, it is clear to me that I reduced the thermal insulation.
That's why I mixed 1 to 4 because I had the feeling that the vermiculite concrete would be not strong (it seemed to me based on the mixed mixture)
It is necessary to sprinkle vermiculite concrete with water because of good hardening, or the moisture it received during mixing is sufficient.
the vermiculib concrete slab is under the roof (the sun does not shine on it)

When mixing vermicrete, particularly the first time, its unusual texture leads most people to be sceptical about its ability to harden up and be strong enough. The correct amount of water is crucial. If too much is added it washes the cement off the grains. If water pools in the bottom of the barrow, then slightly too much water has been added. Because of the huge amount of water required for a vermicrete mix (around 3-4 parts for every 10 of vermiculite by volume), it means that there is well in excess of that which is required for the hydration process. This means that there is no need to sprinkle any water on it or cover it to hold in the water contained. The problem is the elimination of the contained free water.
Vermicrete insulating slab PDF copy.pdf

[bencuch]

Vermiculite concrete ratio 1 to 4, it is clear to me that I reduced the thermal insulation.
That's why I mixed 1 to 4 because I had the feeling that the vermiculite concrete would be not strong (it seemed to me based on the mixed mixture)
It is necessary to sprinkle vermiculite concrete with water because of good hardening, or the moisture it received during mixing is sufficient.
the vermiculib concrete slab is under the roof (the sun does not shine on it)

[david s]

I'm not sure why you want to pour refractory concrete between the floor bricks and the insulation board. There is a difference between concrete and cement. As explained before concrete is a mix of cement, either ordinary portland cement or refractory (calcium aluminate) cement, mixed with an aggregate (vermiculite, perlite, sand or rock), and water. If your "refractory concrete" is a premixed bag of calcium aluminate cement and high temperature aggregate that does not contain any lightweight aggregate like vermiculite or perlite, then it will act as thermal mass to increase the amount of heat storage in the floor. It depends largely on how thick your floor bricks are whether an increase of thermal mass is warranted or not. Generally a 2" thick floor is considered thick enough for general all purpose oven use. Builders sometimes turn the floor bricks on edge to create a thicker floor which makes the oven more suitable as a bread oven which requires more heat storage. The thicker the dense floor material, the longer it takes to heat and the more fuel that will be consumed.
Regarding the 4:1 vermicrete ratio in preference to 5:1, you need to understand that while making it a bit stronger, you have also reduced its insulating capacity (see table) K factor being thermal conductivity. Insulation value is the reciprocal of thermal conductivity. The higher the thermal conductivity the lower the insulating value.

[bencuch]

Hi David s,

Today I peeled off the SUPERIZOL and put 7 cm of vermiculite concrete/perlite concrete as the first layer (half of vermiculite and half of perlite - I had a smaller amount of vermiculite so I mixed it with perlite)
After mixing 1 to 5, it seemed to me that it would have a weak strength, so I mixed 1 to 4 and I'll see when it hardens.
After hardening, I stick 5 cm of SUPERTIZOL (after 1 week).
Since I have refractory concrete left, I am thinking that I would pour approx. 3 to 4 cm of refractory concrete on the SUPERIZOL (larger layer of the floor = it can withstand the heat longer) and then I would lay the bricks.
Do you think it could be?

[david s]

After a better translation, I found out that you already answered my question above. (it is better to lay the floor of the oven freely)

The bricks I bought have small differences in thickness, so I will need to glue them so that the floor is flat - with such a step, it is probably better to put a foil between the floor brick and the SUPERIZOL - AL film so that the floor can expand freely.

As already explained a layer of foil prevents moisture travelling in both directions, so tends to lock in moisture and making its removal harder and slower. Do it if you must, but I think you'll regret it.

If you need to level the floor bricks, builders have found that the best method is a dry mix of sand and powdered clay about 10 mm thick. If made wet, not only are you adding water to an area that needs to be dry, but it glues in the floor bricks thus not allowing them to expand and contract individually. Removing such a stuck floor brick would be very difficult.

[bencuch]

After a better translation, I found out that you already answered my question above. (it is better to lay the floor of the oven freely)

The bricks I bought have small differences in thickness, so I will need to glue them so that the floor is flat - with such a step, it is probably better to put a foil between the floor brick and the SUPERIZOL - AL film so that the floor can expand freely.

[bencuch]

After our conversation, I am thinking that I will put SUPERIZOL down and first pour vermiculite concrete and put Superizol on it (closer to the oven) and then fireclay brick.

Can all the layers be firmly glued together?
Will it be okay for expansion joints - so that the pipe can freely expand and contract when heated?

[david s]

https://armilcfs.com/wp-content/uplo...super-isol.pdf

No sure what type you have, but both of these have a higher compressive strength than a 5:1 vermicrete. In addition to obtain the equivalent insulating value you need to double the thickness of the vermicrete, which means an increased floor height and a larger volume of material.

Also builders have found it better not to mortar down the floor bricks. If they are laid loose it allows for free expansion of individual brick units that will receive different amounts of heat and therefore thermal expansion. If a floor brick requires replacement it's also far easier to do so if they have not been mortared down.

[david s]

"I think vermiculite concrete is stronger than SUPERIZOL."


5:1 vermicrete is around the same strength as insulating board from my experience, but check the specs on it and compare with the attached table.

[bencuch]

That's why I want to put vermiculite concrete on SUPERIZOL to make it a solid layer under the fireclay floor.
I think vermiculite concrete is stronger than SUPERIZOL.

If I were to leave vermiculite concrete over SUPERIZOL, aluminum foil is probably needed between SUPERIZOL and vermiculite concrete.

That's why I think so, because the fireclay brick will be firmly glued to the vermiculite concrete, and during expansion - thermal expansion and contraction, the vermiculite concrete will also expand, and it would not be good if the vermiculite concrete was also firmly glued to the SUPERIZOL.

If I were to replace the SUPERIZOL and the vermiculite concrete as you write, all the layers can stick firmly together.

I appreciate all your advice.

well thank you

[david s]

As you’ve already glued down the insulating board, you’d not want to pull it up, so swapping layers is out. A better solution would be to simply place a second layer of board over the first. Being already dry, it won’t create any issues with having to allow it to dry.

[SableSprings]

As David S recommended in an earlier response, you'd do yourself and your oven a favor by putting your insulated cement mix on your hearth slab and then laying the ceramic board on top. Perlcrete or vermicrete contains a lot of water initially and it takes a long time to drive out. That water needs a path to exit, which is why we recommend weep holes for drainage and mosaic (or broken tiles) between the insulating cement (IC) & the hearth to provide pathways/channels to the weep holes.Besides, the ceramic board is a much better insulation so it makes sense to have it directly under your cooking floor bricks.

Also, by using the weep hole/tile layer on top of the slab, you'll have an effectve barrier fron water that may seep in from the oven's perimeter if water gets onto the top of the slab (rain & sprinklers are common culprits). Putting IC on top of the board means that water will drain down into the ceramic and if you put a layer of foil between them, you'll trap the moisture & make it even more difficult to drive out during your drying/curing fires.

Hope that helps explain this preferred method of oven base design & construction.

[bencuch]

It is necessary to put an aluminum foil on the SUPERIZOL insulation board before pouring the vermiculite concrete (see the picture below from youtube).

I don't think it's important, but I want to get some advice.

Well thank you.