Coating Application and Application Equipment
Airless spray fundamentals
An airless pump pressurizes fluid (commonly 1,500–3,500 psi) through a small orifice, atomizing it without air. Tip notation is reverse-digit: 517 means a 0.017 in orifice and a 10 in fan at 12 in distance (the two fan digits × 2 = fan width at 12 in). Pattern overlap should be about 50%. Tip wear enlarges the orifice, raising flow rate and film thickness while degrading the pattern - a worn tip is a common cause of over-thick, sagging coats. Pump ratio describes the ratio of air or hydraulic input area to fluid piston area.
Technique and controls
Hold the gun perpendicular at a consistent distance, trigger before the stroke and release after it, and stroke parallel to the surface. Stripe coats are brushed into welds, edges, and back-to-back steel before the full coat. Respect induction time (epoxies) and pot life, and apply the next coat within the recoat window or abrade/roughen as the product data requires. Plural-component equipment meters and mixes two-component products; check the ratio and flush procedure.
Wet-to-dry conversion
WFT = DFT × 100 ÷ % volume solids. For 4 mils DFT at 65% volume solids, WFT = 4 × 100 ÷ 65 ≈ 6.2 mils. Check wet film during application, dry film after cure; wet film readings are the earliest correction available.
Traps
Raising pressure to fix a poor pattern usually worsens it - check tip size, filter, hose, and fluid condition first. Environmental limits: RH typically ≤85%, surface at least 3 °C (5 °F) above dew point, and coating temperature within the product data sheet range. Dry spray, orange peel, and sag each point to different causes (distance/solvent, atomization, and film build respectively).