Additives for Castable Refractory

From Refractory Bricks and Refracotry Material

Yellow dextrin is widely used for grinding tool and abrasives, foundry casting, refractory materials, rubber products and other industries, particularly abrasive and refractory materials, refractory charge, light brick, shaped bricks and others, having an superb effect on the early setting of its products. It matches in appropriate proportion and mix well, which plays an excellent role in collapse preventing and edges and corners protecting.

Did I miss something ?

Going to have to give this a try but at what proportion ?


From Binders for Ceramic Bodies

Dextrin also improves the plasticity of clay slips.

and

Darvan

Polymer deflocculant, de-flocculant

Alternate Names: Darvan 811, Darvan No. 7, Darvan 821A, Darvan C

Darvan is a deflocculant and used to disperse ceramic suspensions to minimize their water content. It is a liquid alternative to the long popular sodium silicate. About twice as much is required typically (0.4-0.5%) however Darvan does offer a number of advantages. Typically soda ash is not needed as a complement and Darvan does not attack plaster molds. In addition slurries are much less sensitive to over deflocculation and are more stable. It is thus easier to reprocess scrap. However a number of engineers still prefer using a sodium silicate:soda ash mix to control thixotropic properties better, especially if little scrap is being added.

From 

How to... Make and adjust casting slip This article is interesting because a ceramic slip (casting pottery) and castiable refractories have some things if not much in common. Soda Ash Soda Ash works to dissolve lignite in clay. It works in combination with Sodium Silicate to aid in deflocculation. The correct combination of the two will give proper casting qualities, however, if only Soda Ash is used, your clay will become sticky. If Soda Ash is not stored in tightly closed containers, a chemical change occurs and it becomes Sodium Bicarbonate (Baking Soda). If this occurs it will then act as a flocculant (thickener) instead of as a deflocculant. Super Washing Soda is soda ash.  Have that on hand.