According to the same source the mortar used on the back of the replacement stone veneer should be applied with a pointed trowel.
How to replace siding with stone veneer.
When you re only removing the lower portion of your home s vinyl siding to install a brick or stone wainscot if local code allows you can dig just below grade and bolt angle iron to the foundation to serve as the new brick ledge.
If stones or bricks have fallen off the siding they need to be replaced.
First you can gently remove any stones or parts of stones left in the area.
Mix up a small amount of the concrete mixture.
Angle iron is also necessary above doors and windows to support the brick directly above.
Apply mortar and attach stones once the lath is attached apply mortar to the lath 1 16 to 1 8 thick.
You can use the stiff metal brush to clean the exposed area of wall as well as the stone that has fallen out.
Either the same stone can be put back or a new matching stone can be used.
Hold the stone against the surface for five seconds until it sets.