Cracks at the Lower-Right Corner and Water on the Interior Sill

The crack origin at the lower-right corner maps directly onto what the crew did.

Mallet impacts. The glass edge is the weakest zone on any lite. Striking the edge with a mallet - even a soft-faced one - sends a stress wave into the edge and can create microscopic chips and checks that are invisible at the time. Those flaws become stress concentrators, and the lite fails days or weeks later at exactly that spot.

Forced clearance. The opening is 1/8 in undersized. That means the required glazing clearance is gone at that corner and glass is in contact with metal. Any in-plane load - thermal expansion of the frame, building movement, wind deflection - is transferred straight into a point contact instead of being absorbed by the gasket.

Wedges driven tight. Wedge gaskets locate the lite; they do not clamp it. Driving them with a putty knife preloads the glass in-plane against the corner contact. That is a bending stress in the most fragile part of the assembly.

The three combine: a chipped edge, a hard contact point, and a sustained in-plane load. Any one alone might survive. Together, failure is predictable - and it will keep happening on every opening built the same way.

The rule is simple: glass does not get forced, ever. The opening is corrected, not the glass.

Before setting:

• Measure the opening width and height at top, middle, and bottom, and check both diagonals. Racking shows up as unequal diagonals, not as a narrow number.
• Confirm the actual frame dimension against the glass size and the system's required glazing clearance (5/16 in nominal here) plus gasket compression - that is the number that was violated.
• Verify sill condition: clean, drained, and ready to receive setting blocks.

When undersized:

• Stop. Document the opening with measurements and photos.
• Refer the framing correction to the responsible trade. Adjusting the frame, shimming or re-anchoring the subframe, or moving the rough opening is framing work under the framing contract; the glazing contractor cannot gain clearance by damaging the glass or by over-compressing gaskets.
• If a lite absolutely cannot be installed with the specified clearance, recut or reorder; a 1 in insulating unit is not something to improvise on.
• Never use a mallet on glass, and never use a putty knife as a gasket tool. Use the manufacturer's setting tools and hand pressure.

Also confirm that setting blocks are installed at the quarter points to carry dead load - the drawings omit them, which is a substitution worth a written RFI before the rest of the elevation goes in.

Water running down the inside face of the backup wall points to a flashing and drainage failure, not a failed gasket alone.

Likely path. Rain hits the veneer, enters the cavity, and runs down the backup wall. At the sill it should hit through-wall flashing and be directed out through weeps. If the sill flashing lacks end dams, water runs off the ends of the flashing and into the wall interior. If the flashing laps are backwards (upper piece over lower instead of shingle-style), water runs behind the membrane. If the frame-to-wall joint is not sealed and the sill has no back dam or positive slope, water tracks in past the frame.

Correct sill build, bottom to top:

1. Sill pan / through-wall flashing with a back dam and turned-up end dams at each end.
2. Positive slope to the exterior.
3. Weeps above the flashing, with a mortar-bed or mesh to keep them open.
4. Air seal at the interior side, continuous, behind the frame.
5. Frame set with setting blocks at the quarter points, located so they do not block the weep path.
6. Sealant joint at the frame/sill with backer rod and correct depth-to-width ratio.

Also verify head flashing is lapped over the frame with an end dam, and that the gasket corners were cut and spliced per the system manufacturer. A dry-glaze system still relies on the wall drainage plane behind it.