Powdered clay oven

[ciaranmchugh]

Hi, I'm starting to build my first oven. I've gotten some powdered clay from a pottery friend of mine, I think its slip clay?

I've mixed my first batch last night and used it to cover the layer over my wind bottles and as a base for my fire bricks. I used a mix of 2:1 sand to powder, the consistency seemed good, don't fall apart or splat when ball dropped from waist height.

It's drying slowly today, weather cool. But I've noticed a few cracks appearing as it starts to harden. Not major issue for this layer but worried about actual oven dome if happens again.

Is this normal or what changes should I make to mix?

Thanks in advance for any help

Ciaran

[ciaranmchugh]

[ciaranmchugh]

Images above show where I am at, including small test 'brick' which seems to be holding up ok.   Anyone know If I'm ok or if heading for disaster?

[ciaranmchugh]

Just looking at other posts and saw this "Homebrew is a mixture of Sand/Cement/Lime/Clay in the ration 3-1-1-1 by volume. The first three can be had at any builders yard, the powdered clay can be more tricky but kiln Linings (amongst others) can supply it, as can potters etc".  So my 2:1 sand/clay mix has too much clay and no sand or cement, so hence shrinking.    Will I be ok if leave this 2 inch layer under the firebricks and then mix as per above for the actual oven?  Seems very little clay but I have nothing to base that on. 

Ciaran

[tommyb]

Hi Ciaran
I’ve just joined the forum and read your post. How have you got on?
I’ve been doing my first build during lockdown as a project with my son. We’ve slowly built the brick base, filled with odd bricks then lots of sand into a bottle layer with sand on top & just completes laying the fire brick base. I’ll try and work out how to upload a photo.
I’m looking for advice from here as this is when it gets serious & I’m a bit of a novice to say the least!!
The base measures 91cm square & with the inner fire bricks I’m looking at an internal oven diameter of around 68cm. Do you know how to calculate the height of the sand dome we should aim for?
Any tips on powder clay & how much I’d need?
Can I get away without a fire brick arch?
Any other tips?
Cheers,
Tom

[downunderdave]

If you are making your own castable using the 3:1:1:1 homebrew the usual dome thickness is 50mm with a minimum of 75mm thick insulation layer, normally a combination of ceramic fibre blanket over which is a layer of 10:1 vermicrete. Then an outer rendered shell of around 12-15 mm. You will also require a bit extra at the front of the oven to accomodate a flue gallery. I make ovens on a 910mm square footprint and my internal oven diameter is 540mm. The internal height is usually a hemisphere, half the internal diameter. Very fine polypropylene fibres should be added to the homebrew mix as well. These melt at 160C leaving a network of mini pipes, without reducing the material’s density. They are often used to add to concrete and can be found at specialist concrete suppliers. This provides some protection from steam spalling which can easily ruin your project.

[tommyb]

Thanks For the reply much appreciated.