Application Techniques: Brush, Roller, and Spray
Brush, roller, and spray each have a correct use, and the exam tests selection plus technique.
Brush
Natural bristle for oil and alkyd; synthetic nylon or polyester for waterborne. Cut in 2-3 in and keep a wet edge.
Roller
Nap length matches texture: 1/4-3/8 in for smooth, 1/2 in for light texture, 3/4-1 in for rough, stucco, and masonry. Lay on in a W or N pattern, then back-roll in one direction.
Spray
Airless tips are sized in thousandths: a 517 tip is a 0.017 in orifice with a 10 in fan, run at about 2,000-3,000 psi. Hold the gun 8-12 in away, perpendicular, overlap 50 percent, and keep it moving. HVLP gives a finer finish with less overspray.
Worked example: latex on large flat walls. Choose a 517 tip at roughly 2,500 psi because the 0.017 in orifice passes latex at production speed and the 10 in fan covers width. Too small an orifice causes spitting and forces excess pressure; too large floods the wall and sags.
Traps
- Over-brushing latex, which leaves brush marks and kills film build.
- Wrong nap for the texture.
- Arcing the gun instead of keeping it perpendicular.
- Spraying too close (runs) or too far (dry spray and orange peel).