The first step was to make templates around the fireplace opening. The black metal insert was already installed, with a raised frame at the top and narrow borders along the sides. Below it, the existing dark hearth extended across the floor in front of the firebox. We had to work with those fixed dimensions rather than create a new opening to suit the stone.
We used white template strips to mark the surround on the wall, placing them above the insert and along both vertical sides. The strips followed the intended boundaries of the stone and gave us a way to record the opening dimensions, corner locations, and alignment of the surrounding pieces. We marked the templates with reference lines and X marks so the shop could distinguish the measured edges and their positions.
The upper section needed particular attention because the fireplace frame extended horizontally across the opening. The stone above it had to work with that existing metal edge, while the vertical pieces needed to finish against the sides of the insert. A small measurement error in one section could affect how the adjoining pieces met, even though the total amount of stone was only 13 square feet. This is why I prefer measuring directly from what is installed. A fireplace might appear square when you look at it from across the room, but the wall, framing, and insert can each have slightly different dimensions. In Charleston, we see plenty of houses where walls aren't perfectly straight, even when the surrounding construction looks finished. We check those conditions during templating and work from the actual measurements instead of assuming everything follows the drawing.