Stucco Field Guide
Three layers, about 25 mm in total — each coat has a distinct job, and the middle one carries the reinforcement.
The scratch coat is the first layer, applied at about 10 mm. Its job is bond: it ties the plaster system to the substrate, and its surface is scratched or scored while green so the next coat can grip it mechanically rather than relying on suction alone.
The brown coat is the second layer, also about 10 mm, and it is the structural heart of the system. This is the wire reinforcement layer: the wire is embedded in the middle third of the brown coat, held away from both faces of the plaster.
Placement of that wire is not a detail. Wire against the substrate does nothing for the plaster, and wire at the surface is worse than useless — rusting wire expands, and the expansion pushes the finish coat off the wall. The middle third is where the wire reinforces without ever reaching the weather.
On narrow screens, swipe or scroll the plate sideways.
The finish coat is the last layer, about 5 mm. It carries the texture — float, sand, or another pattern — and acts as the weather face. It can be a Portland-cement finish or an acrylic or elastomeric one; the cement version patches more cleanly, the acrylic versions last longer and tolerate more movement.
Skipping the brown coat is where short systems go wrong. Without it the wall loses its reinforcement layer and roughly half its thickness, so movement that should be spread across 25 mm concentrates in two thin coats — and there is no middle third anywhere to bury wire in. Cracking and debonding follow the missing layer.
Between every coat, the same rule applies: cure damp and shaded, at least 48 hours kept moist per 25 mm of thickness, before the next layer goes on.
Further reading