Use this procedure to mask a ceiling grid. A mask is a polyline shape or space that defines the boundaries of a ceiling grid. Those parts of the grid outside the boundary are not displayed.
- Draw a closed polyline with the boundary or hole shape you want.
- Select the grid you want to mask.
- Click
. 
- Select the closed polyline or space you want to use as a mask.
The parts of the ceiling grid that are outside the masking polyline or space are no longer displayed.
Tip: If you want to restore the original grid shape, go to the Properties palette and select None for Boundary.