Things You'll Need
100-grit sanding belt
One of the most difficult steps in installing a new vanity top is squaring the vanity top to the walls. The walls in older homes become out of square due to settling of the framing. Fortunately, since most vanity tops are either Formica or resin, trimming them is possible. Installing a vanity top with unsquare walls requires a belt sander to trim the edges without damaging the vanity top.
Place masking tape on the top edges of the vanity top. The tape protects the vanity's finish and gives you a surface to mark your scribe line.
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Position the vanity top on top of the cabinet frame. Measure from the front of the cabinet frame to the front edge of the vanity on both ends. Ensure the distance at both ends is equal.
Set a pencil inside the collar of a compass. The compass has a sleeve for the pencil and a pointed end.
Place the point of the compass on the wall where the widest gap is between the vanity and wall. Adjust the pencil arm so the tip of the pencil touches the back edge of the vanity. Twist the locking hub on top of the compass clockwise to lock the compass arms.
Move the compass point to one end of the vanity wall with the pencil tip resting on the vanity top. Slide the compass down the wall to the opposite end of the vanity, allowing the pencil to trace a line on the masking tape.
Pick up the vanity top and place it on a pair of saw horses. Ask your helper to hold the vanity top steady while you trim the vanity top.
Install a 100-grit sanding belt on a belt sander. Sand the edge of the vanity top to the scribe line on the tape. Place the vanity top back on the cabinet frame and test the fit.
Move the vanity top off the cabinet once you have the vanity top square against the wall. Apply construction adhesive to the top of the cabinet frame boards with a caulk gun. Set the vanity top on the cabinet frame. Press down firmly to ensure adhesion between the frame and bottom of the vanity top. Remove the masking tape from the vanity top.
If you have a stone or marble vanity top, a professional must trim the top to fit the walls.