How to Install Stone Window Surrounds

Cover the exterior window stone application area with grade "D" waterproof paper, securing it in place with a carpentry stapler. Space the all-weather staples every 4 inches around the edges and every 12 inches in the center of the paper.

Sand the entire interior area around the window where you will be attaching stone, including the area of the wall that surrounds the window sill. Wipe off all debris and sawdust. Use a stud finder to locate and clearly mark all of the wood supports behind the wall in the area you will be working on. Mark both sides of each stud or support to give a clear picture of the available attachment spots.

Spread out lath across the entire window area, cutting it to fit in place. Overlap any seams in the lath by at least 4 inches. Attach the lath to the wall by drilling 3-inch galvanized wood screws with washers into the marked wall supports, spacing them every 6 inches on each available support.

Spread mortar over the surface of the lath with a trowel until you have a 1/4-inch-thick layer all over the lath. Allow the mortar to dry for three hours.

Scrape the surface of the mortar using a garden fork, scoring every available surface to prepare it for the addition of stones. Let the mortar dry for 48 hours.

Apply a 1/4-inch thickness of mortar to the back of each stone veneer and push them in place against the mortared window area for 30 seconds. Continue to apply the stones, setting the big ones in place first and then working back with smaller stones. Cut any stones as needed to fit them into tight places. Remove any mortar that pushes out from between the stones. Let the stones dry for three hours.

Spread grout between the stones to the depth desired for the chosen appearance. Let the entire area dry for 48 hours.