Fabrication Guide

Planning mirror cutouts, notches and outlets before the glass is cut

A custom mirror rarely lands on a clean, obstruction-free wall. Outlets, sconce boxes, switches and faucets all intrude on the space a mirror wants to occupy, and every one of those intrusions has to be resolved in the design before the glass is cut and finished. This guide covers the strategies for working around fixtures, how edge finishes and templating timing fit in, and where mounting and tolerance realities set limits on what a layout can ask for.

Written by the Gloria Glass installation team

Cutout, notch or split panel: three strategies

When a mirror has to clear an outlet, switch or fixture box, there are three general approaches, and the right one depends on where the obstruction sits relative to the mirror's edge.

Interior cutout — a hole cut fully within the body of the mirror, used when an outlet or fixture sits away from every edge. This is the cleanest look but places the most precise demand on templating, since there is no edge to hide a small error against.
Edge notch — a cut corner or bite taken out of the mirror's perimeter, used when the obstruction sits at or near an edge. A notch is generally more forgiving to template accurately than an interior cutout because it references an edge the installer can measure directly against.
Split-panel layout — breaking a single large mirror into two or more panels with a gap or reveal at the obstruction, rather than cutting around it. This is often the more reliable choice where several fixtures cluster together, since it avoids stacking multiple cutouts into one already-fragile piece of glass.

As a rough guide, isolated single obstructions well inside the mirror favor an interior cutout, obstructions near a perimeter favor a notch, and dense clusters of fixtures — several sconces and a switch, for example — usually favor splitting the mirror rather than turning it into a piece with multiple cuts.

Edge finishes around a cutout

Any cut edge — whether it is the mirror's perimeter or the inside of a cutout — needs a finish, because a raw cut edge is sharp and more prone to chipping. A ground or arrised edge is the practical minimum for a cutout interior, since it is rarely visible once the fixture is in place. Perimeter edges that remain visible, particularly on a frameless mirror with no surrounding trim, generally warrant a polished finish. Where a design calls for a decorative perimeter — bevelled or mitred — that treatment typically stops at the outer edge only; interior cutouts are finished for safety and durability rather than decoration. For a fuller comparison of edge options, see glass edge finishes and fabrication.

Why template timing matters more here than almost anywhere else

Cutouts and notches are fabricated to the exact position of the fixture they clear, and that position has to be locked before the mirror is measured. If a sconce, outlet or switch is going to move even slightly during a renovation, that decision needs to happen before templating, not after. Mirrors with cutouts are essentially unforgiving to a fixture that shifts position later, since the glass cannot be adjusted once it has been cut and finished.

The practical sequence is: finalize fixture and outlet positions, rough in the electrical work, template the wall and every obstruction on it, then fabricate. Templating before the electrical rough-in locks in a position, but the position is only as good as the electrician's own layout, so both trades should be working from the same marked-up plan.

Backing, substrate and how a cutout mirror gets mounted

A mirror with a cutout or notch loses some of the structural continuity of a solid panel, which makes the mounting method and substrate more important than on a plain rectangle. Adhesive mounting needs a flat, sound substrate behind the entire mirror, including around any cutout, since a void or uneven patch behind a cutout edge concentrates stress in exactly the area that is already weaker. Mechanical clips or a J-channel frame reduce reliance on adhesive alone and are often preferred for larger or irregularly shaped mirrors. Whichever method is used, the wall needs to be finished and level before the mirror is installed, since mirrors reflect and highlight any waviness in the surface behind them far more than a painted wall would.

Tolerance realities worth setting expectations around

Cutouts are fabricated with a small working clearance around the fixture rather than an exact-to-the-millimeter fit, both because glass cutting has its own tolerance and because a fixture's cover plate or trim ring typically overlaps the cut edge and hides a modest gap. That gap is normal and expected; it is not a sign that the cutout was measured incorrectly. What is not recoverable is a cutout positioned even a few millimeters off from the fixture's actual location, which is why locking the fixture position before templating matters more than the precision of the cut itself.

Coordinating with the electrical trade

Because the mirror and the electrical work depend on each other's exact positioning, it helps to have one marked-up plan that both trades reference, rather than each working from a separate set of measurements. Confirm box depth and any trim ring or cover plate dimensions in advance, since those determine how much of the cutout the fixture hardware will actually conceal. Any last-minute change to a fixture's position after templating should be treated as a reason to re-template, not a small adjustment to absorb.

A short pre-templating checklist

Every outlet, switch and sconce position finalized and marked on one plan.
Cutout, notch or split-panel strategy chosen for each obstruction.
Edge finish decided for the perimeter and for any cutout interiors.
Electrical rough-in complete and confirmed before templating.
Wall substrate flat, sound and finished ahead of mounting.
Mounting method chosen with the cutout locations in mind.
Fixture cover plate or trim dimensions confirmed with the electrician.

Where to go next

For how mirrors are templated and mounted more broadly, see custom mirror measurement and installation. For edge options and how cutting and finishing fit into fabrication, see glass edge finishes and fabrication. For scope and project inputs, see custom mirrors.