Make a mark 3 feet from the corner on one wall and 4 feet from the corner on the other wall.
Attach countertop to half wall.
Seal any gap between the backsplash and the wall or along the edges and the wall with a clear silicone acrylic caulk.
Reinstall the cabinet doors put the drawers back in place and go have a beer.
If the holes are not completely lining up or you want a more secure install use wall anchors to attach the vanity to the wall.
Cut the boards 2 inches shorter than the depth of the countertop with a circular or table saw.
Attach the vanity to the wall using 3 inch drywall screws.
Using a utility knife cut the cardboard along the scribe line.
The fascia laminates and backsplash can now be added.
Push the strip back tight against the wall using the combination square to verify the overhang depth.
Retape the strip in place.
Attach the countertops to the cabinets.
Run the tip of the compass along the wall with the pencil on the cardboard to transfer the contours of the wall to the strip.
Check the level again before trimming the shims with a utility knife.
If you re working with bare plywood or particleboard place nails vertically down through the top of the countertop spaced about 4 inches.
When you measure for your countertop be sure to include the counter overhang which is usually between 3 4 1 inch in front and on open ends.
Attach three 1 inch by 4 inch wood boards to the wall brace board to hold the countertop.
For a tight fit screw the angles to the cabinet first and then draw the top down to meet the steel angle with the second screw.
If you attach a countertop to the wall with absolutely no cabinets whatsoever then use the same bracing techniques on both sides.
Screw the countertop to the cabinet sides using 1 1 2 in.
The point where two counters meet in a corner must be square.