Capture the Profile
Press a profile gauge against an intact muntin section and the glass, as shown. The gauge’s metal wires slide to create both a positive and a negative replica of the muntin’s profile, which can then be used to make a molding template.
Shown: Mark Powers, TOH senior technical editor, uses a profile gauge to capture a muntin’s undamaged shape. It’s the first step in repairing the scarred portion to the right of the gauge.
Trace the Profile
Place the side of the gauge with the positive profile on a plastic scraper. Line up the edge of the scraper’s blade with the wires that rested against the glass and trace the profile onto the blade face, as shown. Note: If the damage is confined to only one side of the muntin, trace a partial profile in a corner of the scraper blade.
Cut Out the Scraper
Use a coping saw to cut away most of the waste plastic inside the traced line. Fine-tune the edges with a triangular slim-taper file and check your work by placing the cutout over a muntin that hasn’t been damaged.
Mix the Epoxy
Squeeze the epoxy’s two components—resin and hardener—onto a plastic sheet and blend them with a stick for at least 1 minute. Next, stir talcum powder into the epoxy until it becomes stiff enough to hold its shape.
Shape the Epoxy
Protect the glass on both sides of the muntin with strips of painter’s tape. Using an intact scraper, apply the epoxy to the damage. Then place the cutout scraper over the muntin and, holding the scraper square to the glass, slowly drag it through the epoxy. You may need to make a few such passes and add more epoxy to get a clean profile. After each pass, remove any excess epoxy from the scraper and wipe it clean with a rag dampened with white vinegar.
When the epoxy hardens, use a fine-grit sanding sponge to smooth it flush with the undamaged profile.
The next day, wipe the muntin and cured epoxy with denatured alcohol and a clean rag. Brush on an oil-based primer, followed by a top coat or two. Remove the tape before the last coat dries completely.
Mix It Up
The secret to making this kind of repair is to use a slow-setting epoxy, one with a working time of 30 minutes or more. That gives you the opportunity to sculpt the epoxy and match the existing muntin profile before the epoxy turns rock hard and becomes tough to sand.
Most epoxies are too runny for this kind of repair; they need to be thickened with a fine powder, such as talc (shown). Blend in the powder after the two epoxy components are thoroughly mixed. Then keep adding and blending until the compound reaches a firm consistency, like creamy peanut butter. Now you can proceed with the fix.