DSS-Co.04.01 — Mottle / Cloudiness (Spandrel & Back-Paint Systems)

Mottle/cloudiness (spandrel/back-paint) is an appearance change confined to opaque or semi-opaque coatings applied to the non-viewable side of glass (e.g., spandrel back-paint, ceramic frit behind glass, back-coated vision bands). It presents as patchy opacity/density variation, clouding, or tone shifts that are planar within the back-coating and typically non-tactile from the glass side. Classification is appearance-only per VIS (method-agnostic). Inspect after Non-Invasive Reveal on the viewable surface under VIS lighting/geometry; record surface numbering and worked-surface status.

System identification is critical. Confirm coating type (ceramic frit vs. organic back-paint), application location (usually on #2 or #4 surface for spandrel assemblies), and vision vs. non-vision intent.

• Soft, cloud-like mottle across back-paint fields, most obvious in oblique reflections or with behind-glass illumination differences.
• Opacity windows or tone bands where film thickness varies; lap or roller marks possible in long runs.
• Lot or panel repetition suggests process origin; isolated patches may reflect touch-ups or substrate contamination before paint.

Surface-catch class (MSRT)

• From the viewing (glass) side, SC-0 (planar change behind the glass).
• Do not perform MSRT on the back-coating face in situ. MSRT supports classification only on the viewing surface.

Visual signature

• Planar opacity/reflectance variation without surface grooves or pits on the viewing side.
• No chip-flank sparkle, no fused nodules on the glass surface.
• Edge read-through: variations often track application edges, mask lines, or support rails behind glass.

Viewing / lighting

• Evaluate clean & dry at 12 / 36 / 72 in, normal and oblique sweep (~60°-120°); use broad specular and, where permitted, back-lighting (ambient building lighting) to accentuate opacity differences. Record distances/angles in-frame.

Location / access

• Record pane ID and surface numbering (#1-#4; laminate-internal); spandrel/back-paint typically resides on non-exposed faces (e.g., #2 behind air space or #4). If the anomaly is behind the lite or within an IGU, it is inaccessible in place → CAT-5 by location for in-place work scope (classification remains Co.04.01).

Mechanism cue (context)

• Application non-uniformity (wet film thickness, solvent flash), sub-surface contamination before paint, cure/oven variation, or touch-up blends. Absence of field indicators tied to mechanical or chemical attack on the viewing face.

Assign CAT by visibility at acceptance geometry (from the viewing side). Depth values below are apparent optical, not substrate relief.

• CAT-1 (Benign / non-relief): Faint cloudiness legible mainly at oblique/raking; SC-0 at the viewing surface. Indicative relief: 0-10 μm (optical only).
• CAT-2 (Light): Discernible mottle at standard distance in specific lighting; SC-0 viewing surface. Indicative relief: ~10-40 μm (apparent optical).
• CAT-3 (Moderate): Pane-noticeable non-uniformity at standard distance affecting perceived uniformity across a field; SC-0 viewing surface. Indicative relief: ~40-120 μm (apparent optical).
• Reclassify when: If features show ring/run geometry on the viewing face → consider Ch family; if linear chip-flank grooves are present → M.01 scoring; if peppered fused nodules are visible → Th.01 hot particle (on the viewing face).
• CAT-5 (by condition/location): Between-pane or back-paint face inaccessible; or coating-side constraints preclude any in-place correction → CAT-5.

CAT is appearance-based; acceptance is separate under VIS-A at 12/36/72 in. Spandrel/back-paint anomalies are typically system/producer governed; in-place restoration is out of scope when the defect is on a non-exposed face.

• vs. Vision-lite coating anomalies (Co.02/Co.03): Spandrel/back-paint presents on non-vision/opaque zones and reads as opacity density change, not AR/low-E interference shifts.
• vs. Chemical films (Ch): Chemistry on the viewing face shows rings/runs/etch and may yield SC-1/2; Co.04.01 remains planar SC-0 on the viewing surface.
• vs. Abrasion fields (M.02): Abrasion has directional texture and SC-1; spandrel mottle lacks surface relief.
• vs. Substrate defects (P.02/P.03): Seeds/striae modulate transmission but do not create opaque paint mottle boundaries.

• Photo set (VIS): 12 / 36 / 72 in, normal + oblique; broad specular and ambient back-lit frames to show density differences; raking macros confirming smooth viewing surface. Record distance/angle in-frame.
• Face/System ID. Confirm spandrel/back-paint face and system build (shop drawings, submittals).
• MSRT (viewing surface only). SC-0 expected; record result to distinguish from surface abrasion or chemical attack.
• Lot/replication check. Document adjacent units for pattern repetition to support producer-intrinsic origin.
• Forms: Pane ID; product family & surface numbering; worked surface Y/N; functional/back-paint coating on worked surface? (Y/N/Unknown); reveal status; lighting/time; geometry checklist; photos attached.
• Acceptance split: Post-restoration acceptance per VIS-A §6 (viewing geometry); classification ≠ acceptance. Non-exposed coating faces are typically outside in-place restoration scope.

• Co.04.01 Mottle / Cloudiness (Spandrel/Back-Paint) - Planar opacity non-uniformity/clouding behind glass on surface #___ (back-paint/frit system confirmed); MSRT (viewing face): SC-0; visible at [12/36/72 in] under VIS geometry and [oblique/back-lit]. Morphology: cloud-like density variation, no chip-flank grooves, no surface pits. Classification: CAT-[1/2/3] by visibility; CAT-5 if between-pane/back-paint face inaccessible; reclassify only if viewing-face mechanical/chemical indicators are present. Forms + photo set attached; acceptance per VIS-A §6.