When laminating an L- shaped countertop, it's fine to butt two factory-cut pieces together, as long as the legs meet at 90 degrees. But it's better to join them with a miter that looks elegant and doesn't depend on the L being perfect. To get a tight miter, both edges have to line up exactly. "Mirror-cutting," a technique in which you cut both pieces simultaneously using a laminate trimmer and a straightedge, guarantees that they will. Here's how to do it.
1. Before rough-cutting the two pieces of laminate, make sure that each piece will cover an entire leg (you want them to overlap in the corner you plan to miter), and that they will overhang the countertop's edges by exactly 1 inch. Spring-clamp the sheets to the cutting table, then use a laminate trimmer fitted with a flush-cutting bit to trim them to size. (For tips on how to do this, see Step 2 of Step-by-Step.)
2. Cut a triangular scrap of plywood so two adjacent edges fit tightly against the inside corner of the countertop. Clamp it to the cutting table. This will let you set the sheets at the same angle as the countertop. Overlap the two sheets so their outside corners meet at the same point, then butt their inside edges against the scrap. Clamp each sheet securely to the cutting table, remove the scrap, and use a straightedge to mark a line on the top sheet that goes from the outside corner to the inside corner.
3. Set the trimmer's straight-cut bit just deep enough to penetrate both sheets. Clamp a straightedge parallel to the cutline to guide the trimmer, then make the cut in a single pass down the center of the line, as shown. Bevel the underside of the cut edges with two swipes of medium-grit sandpaper.
4. Using the straightedge, draw a line on the countertop between the L's inside and outside corners. Spread contact adhesive on the countertop substrate and both sheets of laminate. When it dries, set a sheet on dowels placed on the substrate. They let you position the sheet exactly before gluing it down.
5. Press the laminate's outside corner into the cement alongside the line. Pivot the sheet until its mitered edge lines up with the line on the counter, then press the entire edge in place, working from the outside to the inside corner. Take out the dowels as you hand-press and J-roll the sheet from the miter to the opposite end. Now set the second sheet on dowels and align the corners of its mitered edge with those of the first sheet. Press one corner into the cement, then butt the rest of the edge tightly against the first sheet, working from corner to corner. Finish by pressing and rolling the second sheet securely into place.