Amount of fibres needed

[hughesyourdaddy]

Hi all,

I'm planning on building a 30" castable oven and I'm wondering approximately how many kilos of polypropylene fibers and stainless steel needles/melt extract fibers I should include in my mix.

Thanks

[david s]

That depends on the volume of material in the cast which in turn depends on the oven wall thickness. 4/3 pi r3 for volume of a sphere, don't forget to halve it because it's a hemisphere. (the volume of the oven mouth is equivalent to the part that surrounds the mouth so just work on the total volume of a hemisphere. Generally most cast ovens are 2" thick.

You also need extra to cast the flue gallery.

Stainless needles should be between 2-4% of the dry weight of the castable. for the fine polypropylene fibres you don't need much, around half a handful for every 10 litres of castable but make sure they're well dispersed.

[hughesyourdaddy]

Thank you David. I'm sure I'll have more questions soon!

[hughesyourdaddy]

david s

I'm struggling to find a source locally for fireclay. I have a lot of older red bricks which are just your standard building bricks. Could these be crushed up and used in place of fireclay in the homebrew mortar mix?

[david s]

No, crushed fired brick essentially just becomes an aggregate in mortar. You need the stickiness of the powdered clay. The clay is sometimes called bricklayers clay, so contact a bricklayer to de if they can point you in the right direction. Failing that try a pottery or ceramics supplier, they use powdered clay all the time. Ask a local potter where they get their supplies. Don’t ask them for fire clay though because to a potter fire clay is a clay that will withstand extremely high (>1300C) temperatures. Ask them for the much cheaper Ball Clay.