Rough the entire surface where stone will be applied with sandpaper. Use a stud finder to mark the locations of the studs in those areas of the doorway.
Cover the area with lath and drill holes every 12 inches into every stud in the wall. Set 2-inch wood screws in the drilled holes with plastic washers attached. Drill the screws into the holes using a drill. Space the screws every four inches along the edges of the lath.
Apply mortar to the lath using a trowel. Add mortar until it is built up to a 1/4-inch layer.
Start at the top and begin applying stone veneers one at a time by applying a thin layer of mortar to the application surface and then pressing the stone hard against the lath for 30 seconds. Repeat to install each stone in the archway one at a time. Cut any stones that require shaping using a saw with a masonry blade. Begin with larger stones and then go back and fill in the gaps using smaller ones.
Squeeze grout into the cracks between the stones after the entire archway has been applied. Allow the grout and the mortar to set overnight before moving on with any additional projects around the archway.