How Do I Prepare an Older Kitchen for New Countertops

The scrape of a shovel against plaster and the crack of old tile coming off a wall is the sound of a tear out going wrong, and it is avoidable with preparation done before anyone touches the counter. In Richmond, VA, the houses in the Fan District and out toward Maymont carry settled floors and plaster walls, and the countertops going into them depend on what is done first, as the notes kept at countertops richmond becoming bulletproof movie make plain.
Cabinets come first

Cabinets must be fully installed, level and secured to the wall before templating, because the template records the cabinet tops exactly as they sit. Anything moved afterward changes the fit. Whether a given run can carry granite or quartz should be checked on the box, not assumed, and weak or sagging frames get reinforced before stone is set.
Floors that have settled

Older houses often have floors that have dropped over the decades, and base cabinets follow them out of level. Shims under the cabinet boxes bring the tops back to level before the slab goes on. Fixing it with thick adhesive under the stone is the wrong place to take up the difference.
Walls that are not flat
Walls in old homes are frequently out of square or not flat, and that shows up as a gap at the back edge. There are two ways to handle it. The stone can be scribed along the top so the back edge follows the wall, or a backsplash can cover the gap. Which one suits depends on how large the gap is and on the edge profile chosen for the front, whether an eased edge or a bullnose.
Fixtures on site
The sink, faucet and cooktop models should be chosen and on site at templating, since cutouts are sized to the actual fixtures. A catalogue drawing is not the same as the real sink. An undermount bowl, a drop-in rim and a slide-in range each need different reveals and clearances, and the overhang at a seating edge is set at the same visit.
Access and tear out
Narrow stairs, tight hallways and doorways limit how large a single slab piece can be carried in, and that can force a seam. A seam is not a sign of poor work. Good seam placement puts the joint where the piece must break anyway, away from the sink cutout where possible. A remnant can suit a small vanity or bar, but a long kitchen run needs a full slab plan.
Old countertops must be removed carefully, because plaster walls and old tile backsplashes can crack or pull away during tear out. Score the caulk line, cut the adhesive, and lift in sections. The shutoff valves under the sink should turn properly before demolition, so the sink can be disconnected safely. A seized valve is replaced first, not forced on the day.