Fillers and Binders:

The investment materials utilized to produce slurry for coating the pattern are separated into two categories generally. Fillers are the materials utilized to hold the refractory particles together as fluid-like slurry. Binders give the fundamental mould refractory material. Slurries are prepared by adding up the flour filler or refractory powder to a binder liquid and then utilizing adequate agitation to break up agglomerates & to thoroughly wet and disperse the powder. Mixing remained continued until the viscosity of the slurry attained the proper level for coating the pattern. Continued stirring is needed in production to keep the powder from settling out of suspension. Either propeller mixers  or rotating tanks are utilized for this purpose.

As a common rule, ethyl silicate is not utilized as a binder for the first & second coats of the ceramic shell procedure, because the drying rate is too quick and shell surface cracking results through the stress caused by thermal expansion of the refractory. While mixing the slurries, the refractory flour is added up to the binder to make sure good dispersion of solids. In order to get good coverage of the patterns, a wetting agent must be used for the first ceramic shell coat.