Book 3 — Cement Grotto for an Aquarium

To build a small cement grotto for an aquarium, make a clay mold by roughly excavating two right-angled gutters in a lump of clay. Grease, or shellac, the mold after it is dry. Apply cement of about the consistency of putty, or dough, filling the gutters roughly so as to give a rocklike finish. Small shells can be stuck into the cement while it is yet moist. Before entirely shaping the cement, a piece of heavy wire is bent to conform to the shape of the grotto and set in for a reinforcement.

Cement Grotto Roughly Molded over Clay, Shaped to Make the Right Form

Holes can be made by twisting paper, so that it will extend out at each side, and laying cement over it. After the cement is thoroughly dry, the paper can be removed in sections.