A contractor is applying a two-coat elastomeric coating to a CMU commercial building.

You will have coating failure within 1–3 years. Here is the specific breakdown:

1. Insufficient Film Thickness (Critical)

• Spec: 12–14 mils WFT/coat = 24–28 mils total WFT.
• Applied: ~8 mils WFT/coat = ~16 mils total WFT.
• Result: You are ~35–45% below spec. Elastomerics rely on high dry film thickness (DFT) for elongation and waterproofing. At ~10–12 mils DFT (assuming 50% solids), you lack the membrane thickness to bridge active cracks or withstand thermal cycling. Expect cracking, pinholes, and water intrusion.

2. No Back-Rolling on CMU (Code/Standard Violation)

• ASTM D6947 / Manufacturer Specs: Airless spray requires back-rolling on porous, profiled substrates (CMU) to force coating into pores, bug holes, and hairline cracks.
• Result: Pinholing and voids at the substrate interface. The coating bridges the texture rather than wetting it. Water sits in the voids, freezes, and pops the film (osmotic blistering).

3. Recoat Window Violation (90 Minutes)

• Chemistry: Most elastomerics (acrylic/silicone) require a minimum 4–24 hour cure before recoat. "Dry to touch" ≠ cured.
• Result: Solvent entrapment & intercoat delamination. The second coat seals solvents/water in the first. The film stays soft, dirt picks up, and layers separate under thermal stress.

4. Hairline Cracks > Coating Capability

• Elastomerics bridge static cracks up to ~1/16" (1.5mm) only at full spec DFT (20+ mils DFT). At your DFT, they will telegraph through immediately. Repair required: Rout and seal with polyurethane sealant (ASTM C920) or cementitious patch before coating.

5. Parapet Cap Missing Flashing (Structural Defect)

• IBC 1404.2 / NRCA: Parapets require through-wall flashing and drip edges. Coating is not flashing.
• Result: Water enters the wall top, migrates down behind the coating, and causes widespread delamination and efflorescence at the parapet and upper walls.

Fix: Stop. Remove loose coating. Repair cracks properly. Install parapet flashing/coping. Re-apply at spec WFT with back-rolling. Observe recoat times. This is a re-do.

The contractor’s approach will likely result in premature coating failure due to multiple critical errors:

1. Insufficient Wet Film Thickness (WFT): Spec requires 12–14 mils WFT per coat. Spraying only 8 mils WFT means the dry film thickness (DFT) will be roughly 40–50% of required (assuming ~50% solids). Two coats at 8 mils WFT each yield ~8 mils DFT total—far below the 12–14 mils DFT per coat needed (24–28 mils total DFT). Elastomeric coatings rely on adequate thickness for crack bridging, UV resistance, and waterproofing. Thin films will crack, chalk, and fail prematurely.

1. No Back-Rolling: Spray-only application on porous CMU leaves uneven coverage, pinholes, and thin spots. Back-rolling (or back-brushing) is essential to work the coating into pores and achieve uniform thickness. Skipping this violates best practices (per ASTM D4263 and manufacturer guidelines) and guarantees inadequate substrate sealing.

1. Second Coat Applied Too Soon: Applying the second coat at 90 minutes—based only on “dry to touch”—is too early. Elastomeric coatings require full solvent/evaporative cure (typically 4–24 hours, per product data sheet) to avoid lifting, wrinkling, or poor intercoat adhesion. Applying over a tacky surface traps solvents and causes blistering or delamination.

1. No Flashing at Parapet Cap: Missing flashing allows water intrusion behind the coating, leading to blistering, substrate damage, and eventual coating failure at the parapet— a common leak point.

1. Hairline Cracks: While elastomeric coatings can bridge hairline cracks (<1/16"), insufficient thickness (as above) negates this benefit. Cracks will telegraph through the thin film.

Result: Early failure—peeling, cracking, water infiltration, and costly rework. Correction: Use proper tip size (e.g., 515–521 for elastomerics), apply 12–14 mils WFT per coat with back-rolling, follow recoat times per TDS, and install flashing at parapet. This is not a DIY fix—consult the coating manufacturer’s rep and consider involving a licensed waterproofing specialist if warranty or code compliance is at stake.

(References: ASTM C1060, ICC-ES AC212, typical elastomeric coating TDS from Sherwin-Williams, BASF, or Henry.)