Eggshells can be used as fertilizers, cement and tile binder and paste ingredient after grinding them finely. They contain calcium, phosphorus, potassium and sulfur which makes plants robust and vigorous.
Ground eggshells can also be used as a reinforcing ingredient in pastes. Mixed with starch, the sticky substance can bind paper effectively. When used as a cement binder, the mixture dries easily and as tile binder, it gives a hard but smooth finish. One part white cement is mixed with every two parts ground shell.
Source: Phil. Farmer’s Journal March 1981