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gemunden 06-07-2009 10:49 AM

Fireclay questions and Oven floor problems
 
So i just finished the vermiculite layer and am about to get started placing the bricks on top of it. Unfortunately, this is my second time doing this part of the process because my last vermiculite layer did not hold together well enough. I have since then fixed that problem but and still unsure of how the next part of the plans is supposed to work. As i understand it, a thin layer of fireclay is mixed together and then the bricks are set in that making sure that they are all level. What i do not understand is how come this layer does not dry and harden. Is that supposed to happen? Secondly, if it is then wont all my bricks get messed up when i put the first layer of the oven wall on top of them? If anyone could just explain this part of the plan in more depth and detail than the online plans state that would be amazing.

lou

Les 06-07-2009 11:07 AM

Re: Fireclay questions and Oven floor problems
 
Lou,

You don't mix the fireclay - just screed it of with a notched trowel and level the brick. A lot of us didn't build the dome on top of the hearth brick. My reasoning was that if you ever need to replace one (and I don't see the need for that now) it could easily be replaced. If you choose to build on top of them, and it does compress, it will be such a small amount around the perimeter that it will not affect your cooking. Does this make sense?

Les...

gemunden 06-07-2009 11:30 AM

Re: Fireclay questions and Oven floor problems
 
I was hoping to build my dome on top of the oven floor made of fire bricks, but if the fireclay under the bricks never hardens then would this be a bad idea? It seems so much easier than having to cut the bricks making up the floor all so that the floor fits perfectly inside the dome. and even if i did do this i would need to put something else under the first layer of bricks that would go on top of the vermiculite so that that layer was level correct???

Lars 06-07-2009 01:07 PM

Re: Fireclay questions and Oven floor problems
 
Hi Gemunden,
I guess I am just slightly further along than you, but I will point you to my thoughts on mortar, oven floor, etc.

I laid a 2.5" circular layer of vermiculite/portland on the hearth. ( I believe it was something like 4:1: (1/2 lime) verm: portland.)

Then I laid out the floor bricks in herringbone pattern. I mortared them in using a refractory mortar and soon found out that the mix I had originally planned to use would work MUCH better for my oven.

I then laid out the first chain ( on TOP of the floor bricks) and the whole thing rests on the insulating layer.

The fireclay/portland mortar ( and this is my understanding) is like a two stage mortar. In the first stage, it is great to work with. Almost fluffy, and can be quite sticky. The Portland sets up and keeps the rain from washing out the clay. Be sure to use fine sand, as all purpose sand can have quite large gravel in it.

As you use your oven and consistently bring it up to temperature, the portland cement fails, and the clay, ( I am hoping) starts to get fired, as it were, and take on a more solid, and water resistant qualities. It may not have as good of adhesion, but should keep the firebricks in place.

Long answer, and whoever reads this, let me know if my basic understanding is sound, or flawed.

The above is why I chose to mix twice the fireclay to portland. I call it my 3:2:1: and (1/2) mix... Finesand:fireclay:portland:lime ( not that much lime) Because this is PLENTY strong to work with in the construction phase, and the clay content is the ultimate agent for bulk and bonding.

Anyway, that is my understanding.

Lars.

gemunden 06-07-2009 09:01 PM

Re: Fireclay questions and Oven floor problems
 
So the bricks for the oven floor are layed into place using mortar than? I was under the impression it was a fireclay types mixture. I have messed this step up in the past because my mixture did not harden and so my floor became all crocked when i placed the first chain on top of it.

Rastys 06-07-2009 11:55 PM

Re: Fireclay questions and Oven floor problems
 
gemunden
why not cut some full sized fire bricks with a 15˚ cut off the inside top of the brick and lay then either mortared or dry on top of your vermiculite/cement insulation layer, Mortar them together to form your first or as they call them your 'soldier course'.
With the tops cut at 15˚, your next chain is very easy to place and again mortar them on. Now you can lay your hearth bricks on a thin but soft dry sand or fire clay bed, tamping them gently to be all flat, level and the same height, You can cut the outer bricks to fit and they don't have to fit 'perfectly' as you can't use this area to cook on as your fire is usually located there. On the other hand, you also don't want an inch gap either. Once your hearth is in place, sprinkle it with sand or cover with plywood or cardboard to keep it clean and complete your remaining chains.

Rastys


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