Painting Application Techniques and Finishing
This domain covers how a coat is actually laid on - brush, roller and spray technique, the order of coats, drying conditions, and how defects such as sags, brush marks and holidays are prevented.
The system, not a single coat
Prepare → prime → fill and sand → undercoat → two finish coats. Each coat must be dry, lightly sanded and dusted before the next. Film thickness per coat is typically 35–50 microns dry; a thin, even film outlasts one thick coat.
Technique
- Brush: dip one-third of the bristle, tap off excess, cut in a 50–75 mm band along edges, then lay off in one direction with light strokes. Work from dry areas into wet.
- Roller: load evenly on the grid, apply in a W pattern, spread without over-rolling, and keep a wet edge to avoid lap marks.
- Spray: hold the gun 200–250 mm away, perpendicular, 50% overlap, correct viscosity and tip size.
Conditions
Apply between about 10 °C and 35 °C with relative humidity under 85%, out of direct sun and strong wind, and with the surface at least 3 °C above the dew point. Respect the stated recoat interval.
Worked example
Emulsion with a 4-hour recoat, 46 m² to receive two coats. Reasoning: coats cannot be compressed into one day. Plan first coat 8:00–11:00, second coat from 15:00, checking humidity and that the first coat is fully matt and dry to touch. One thick coat would sag and dry unevenly.
Traps that cost marks
Over-brushing fast-drying emulsion; painting in direct sun, causing lap and flash marks; removing masking tape from wet paint; recoating before the interval; leaving holidays in a gloss coat.