Base built and hearth poured.....now Im stuck.

[Eddie4]

I have poured a 6" concrete slab for the oven base. (no vermiculite mixed in)

My plan was to use insulated board then firebrick before I set the oven floor.

Can someone walk me thru that process?

1" board, then I mortor firebrick to the board or dry stack that?
how do I keep the board from getting wet in the weather.

Any help would be great.

Thanks,

Ed

[clg763]

Re: Base built and hearth poured.....now Im stuck.

First of all, the entire oven should have something to protect it from moisture, the board just goes inside of that enclosure.

It is up to you if you want to mortar the bricks to the board, I recommend that you dry stack them so you can replace any defective bricks down the road.

1" board is pretty thin if you don't have an insulated vermiculite concrete base, the going recommendation here is 2" thick as a minimum.

[Eddie4]

Re: Base built and hearth poured.....now Im stuck.

so, i think im going to go with a 1" ceramic board on the concrete slab followed by a layer of insulated fire brick, then the oven floor.

any advice on weather or not "hard fire brick" vs "insulated fire brick" will make a huge difference?

Thanks,

Ed

[shuboyje]

Re: Base built and hearth poured.....now Im stuck.

Hard fire brick and insulating firebrick serve two very different functions in an oven. The goal is to have a oven core built of brick or some other refractory material with high thermal mass to absorb and store heat surrounded by insulation to hold the heat in and focus it where you want it, the oven interior.

Hard brick is your thermal mass, soft brick is a form of insulation. Generally soft brick is not used because it is expensive and doesn't offer any better performance then cheaper options like perlcrete.

If you already have the the 1" board, I would pour 4" of perlcrete, then put your 1" board on top of that, and finally your cooking hearth made of hard firebrick.

[Faith In Virginia]

Re: Base built and hearth poured.....now Im stuck.

Eddie4, This is what I would do.

Starting at your concrete slab moving up.

First you need an insulation layer 2" of ceramic board. If you want to make a mix then you can use the 1' of ceramic board and the insulating bricks (I would stand them on edge).

You can also use a vermiculite/Portland cement mix and go at least 4"

Use one of the three methods. Then

Set you hard firebrick floor. I would not mortar them in. You will find that the insulation layer is not absolutely flat and your firebrick does not have an absolute thickness so it makes it difficult to get a flat floor. You want your floor to be even in height because if you have an edge or corner of a brick raised every time you slide your peal in that raised edge will catch and prevent a smooth slide of the peal.

So what you do is make a mix of sand and fireclay and water. I'll have to look for the ratio. But you lay your floor the same as you would lay floor tile. Use a notched trowel and screet out the fireclay sand mix and set your floor firebrick. This allows you to tap the brick to get them all even.

Hope that helps.

[Neil2]

Re: Base built and hearth poured.....now Im stuck.

"how do I keep the board from getting wet in the weather."

The above information on insulation options is spot on.

With respect to keeping the insulation dry there are several thing you should consider.

- The insulation layer(s) should be protected from precipitation. The insulation layer on your suspended slab should not extend to the limits of the slab, only to the area under the actual hearth and dome.

- You should have positive drainage of the top of the slab. Water and moisture will get in from time to time. Test the top of the slab with a bucket of water - it should drain away completely with no "bath tubs" left. If not, take an angle grinder to it so the low spots drain.