How to Cut Holes for Duct Work in Rock Lath

Rock lath, a type of gypsum wallboard, is often used as a substitute for plaster and can be used as a top layer over metal ductwork. The material is similar to drywall and is typically 3/8 inch thick. To allow for proper ventilation and prevent mildew from growing in your ductwork, cut holes for your ductwork to breathe. It’s important to wear thick gloves and safety goggles when using a drill and cutting rock lath.

Thick gloves
Safety goggles
Pencil or marker
Circle stencil
Metal snips
Drill
1/8-inch and 3/8-inch metal drill bits

Instructions

- 1
  Outline the size of the hole that you wish to remove from the ductwork using a pencil or marker. A circle stencil may be used to achieve exact measurements.
- 2
  Drill a starter hole using a 1/8-inch drill bit. The hole should be created just inside of the circle outline. Drill the same hole using a 3/8-inch drill bit to make a bigger hole.
- 3
  Insert the tip of your snips into the hole.
- 4
  Cut the ductwork using the metal snips, following the circular outline. Continue cutting along the trace line until the hole has been completely cut and removed.

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