Homemade refractory recipe

[Bentiron1946]

I have done bronze cast for several years with home made furnaces of varying size made from fire brick and fire clay or from fire clay, silica sand and Portland cement. The ones that have lasted the longest have been the ones out of fire brick. I usually pour my bronze when the pyrometer reads 2,450f so the furnace has to be some hotter then that. The problem with clay, sand and cement furnaces seems to be cracks that developed from heating and cooling over time. These have to be continually patched. The furnaces of both types have to dried out very slowly or expansion of moisture in the refractory will cause explosions. The Portland cement helps the castable refractory flow and mix better then the straight clay in my experience. Very little is required to help mix the sand and clay together with a minimum of water. It should not be so much pourable as packable.

[FritzDaKat]

Unfortunatly all I've got in any quantity right now is a rather abundant supply of a natural reddish-tan clay which closely resembles basic potters clay after a good washing, as in flower pot type. So using this, other than frequent patching are there any other concerns I should have? (pretty handy with a trowel )

Would adding drill turnings help any or hurt? (I've seen it suggested but this was for adding to fireclay) And considering I'm washing the clay, would it be best to add the wood ash and whatnot while the clay was still in a slip form or would I do better to blend it in after washing / drying was done? And any thoughts on adding crushed flint to the mix? I know it does wonders for thermal limits in glass but mabey I'm just being too wishful?

Yea' I know I should just go buy some fireclay, but money is in very short supply for me a.t.m.

[Dragonforge]

Fritz. Do yourself a favour. There is stuff on the market called mouldable ceramic fibre. Basically it is chopped ceramic fibre mixed into a sticky mois clay base (White). After finishing your furnace, coat it with this. It will need to air dry for about 2 days (when packed 1 1/2 cm thick. It becomes hard and insulates very well. this causes the furnace to heat and cool at a slower rate largely reducing cracking caused by temperature fluctuations.