Watertight Geometry

Watertight geometry means that there are no holes or gaps in your geometry. As you can see in the picture below the cube is missing some of its faces causing it to not be ‘watertight’. When you go to look at this model in the 2D view in Z print it will appear that nothing will be printed because the 3D printer will attempt to print the very thin planes that make up the sides of the cube instead of the whole cube as a solid.

(Click to Enlarge)

To correct this problem you will need to add the faces that are missing on the geometry until there are no holes or gaps in the geometry.